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Molecular genetics of desiccation and tolerant systems
Abstract
This multi-author book gives a comprehensive account of desiccation and plant survival, and of how plant cells deal with extreme water stress. There is a general introduction on desiccation, and then four sections dealing with: The technical background to desiccation studies; the frequency and levels of dehydration stress tolerance in biological systems; mechanisms of damage and tolerance; and a brief retrospect and prospect. Orthodox and recalcitrant seeds, pollen and spores, vegetative parts, and other plant tissues are covered in detail.
... At this point it is worth, for the sake of contrast, briefly discussing mechanisms of vegetative desiccation tolerance that are seen in the angiosperms. As mentioned above, vegetative desiccation-tolerant angiosperms can only survive desiccation if the rate of dehydration allows for the establishment of cellular protective measures , Phillips et al. 2002. The early phase of drying in the desiccation-tolerant angiosperms is marked by a major switch in transcriptional activity, resulting in the generation of a large number of novel transcripts, which in turn generate proteins specific for the drying phase (Ingram & Bartels 1996, Phillips et al. 2002, Collett et al. 2004). ...
... As mentioned above, vegetative desiccation-tolerant angiosperms can only survive desiccation if the rate of dehydration allows for the establishment of cellular protective measures , Phillips et al. 2002. The early phase of drying in the desiccation-tolerant angiosperms is marked by a major switch in transcriptional activity, resulting in the generation of a large number of novel transcripts, which in turn generate proteins specific for the drying phase (Ingram & Bartels 1996, Phillips et al. 2002, Collett et al. 2004). The induced change in transcriptional control reveals a broad range of dehydration-regulated genes that have an equally broad range of putative functions, testament to the severity of the stress and the complexity of the interactions between cellular processes designed to deliver tolerance (Phillips & Bartels 2000). ...
... The induced change in transcriptional control reveals a broad range of dehydration-regulated genes that have an equally broad range of putative functions, testament to the severity of the stress and the complexity of the interactions between cellular processes designed to deliver tolerance (Phillips & Bartels 2000). The induction of gene expression in response to dehydration in desiccation-tolerant angiosperms involves two classes of signal induction pathway, one that is controlled by the plant hormone abscisic acid (ABA) and the other ABA-independent (Phillips et al. 2002, Ramanjulu & Bartels 2002. Endogenous ABA concentrations increase in vegetative tissues in response to dehydration in all angiosperms studied to date, even those that are sensitive to this stress (Bray 1997). ...
Bryophyte Biology provides an extensive overview of the hornworts, liverworts, and mosses; diverse groups of land plants that occupy a great variety of habitats throughout the world. This new edition covers essential aspects of bryophyte biology, from morphology, physiological ecology and conservation, to speciation, and genomics. Revised classifications incorporate contributions from recent phylogenetic studies. Six new chapters complement fully updated chapters from the original book to provide a completely up-to-date resource. New chapters focus on the contributions of Physcomitrella to plant genomic research, population ecology of bryophytes, mechanisms of drought tolerance, a phylogenomic perspective on land plant evolution, and problems and progress of bryophyte speciation and conservation. Written by leaders in the field, this book offers an authoritative treatment of bryophyte biology, with rich citation of the current literature, suitable for advanced students and researchers.
... ABA plays a key role in the initiation of DT resulting in expression of proteins [117,118]. Several dehydration-regulating genes are linked to ABA in DTplants [72,[119][120][121]. Regulatory pathways and gene signalling information in resurrection plants are relatively unknown in comparison with Arabidopsis. ...
... Also, these proteins are present in yeasts, bacteria [134,135], nematodes [136,137], and fungi [138,139]. It has also been shown that ABA regulates the LEA protein expression along with dehydration-induced genes [72]. In C. plantagineum, a minimum of two LEA proteins (CDeT 11-24 and CDeT [6][7][8][9][10][11][12][13][14][15][16][17][18][19] are phosphorylated in vivo during desiccation [140]. ...
Resurrection plants possess a unique ability to counteract desiccation stress. Desiccation tolerance (DT) is a very complex multigenic and multifactorial process comprising a combination of physiological, morphological, cellular, genomic, transcriptomic, proteomic, and metabolic processes. Modification in the sugar composition of the hemicellulosic fraction of the cell wall is detected during dehydration. An important change is a decrease of glucose in the hemicellulosic fraction during dehydration that can reflect a modification of the xyloglucan structure. The expansins might also be involved in cell wall flexibility during drying and disrupt hydrogen bonds between polymers during rehydration of the cell wall. Cleavages by xyloglucan-modifying enzymes release the tightly bound xyloglucan-cellulose network, thus increasing cell wall flexibility required for cell wall folding upon desiccation. Changes in hydroxyproline-rich glycoproteins (HRGPs) such as arabinogalactan proteins (AGPs) are also observed during desiccation and rehydration processes. It has also been observed that significant alterations in the process of photosynthesis and photosystem (PS) II activity along with changes in the antioxidant enzyme system also increased the cell wall and membrane fluidity resulting in DT. Similarly, recent data show a major role of ABA, LEA proteins, and small regulatory RNA in regulating DT responses. Current progress in “- omic ” technologies has enabled quantitative monitoring of the plethora of biological molecules in a high throughput routine, making it possible to compare their levels between desiccation-sensitive and DT species. In this review, we present a comprehensive overview of structural, physiological, cellular, molecular, and global responses involved in desiccation tolerance.
... Plusieurs études physiologiques ont démontré que l'accumulation des sucres et des polyols, principalement suite à l'hydrolyse de l'amidon (Hoekstra et al. 2001; Phillips et al. 2002), était stimulée par un stress salin chez différentes espèces végétales (Gilmour et al. 2000; Streeter et al. 2001; Taji et al. 2002; Bartels et Sunkar 2005; Majumder et al. 2010). Une forte corrélation a été établie entre l'accumulation des sucres et le niveau de tolérance à la salinité (Gilmour et al. 2000; Streeter et al. 2001; Taji et al. 2002; Bartels et Sunkar 2005). ...
... Une forte corrélation a été établie entre l'accumulation des sucres et le niveau de tolérance à la salinité (Gilmour et al. 2000; Streeter et al. 2001; Taji et al. 2002; Bartels et Sunkar 2005). Les nombreux cas où sont décelées des accumulations de sucres (saccharose) ou de leurs dérivés alcools, tels que les polyols, le mannitol, le sorbitol et le tréhalose (Phillips et al. 2002; Sairam et Tyagi 2004), s'accompagnent aussi de l'augmentation de composés aminés (Cushman 2001). L'augmentation de la concentration des polyols entraîne une augmentation du potentiel osmotique du cytoplasme, ce qui permet une plus grande compartimentation de sodium dans la vacuole. ...
Abstract The problem of salinity is multiple. In addition to salt stress, ion toxicity (Na+ and Cl- dissolved in irrigation water or in soil solution), and mineral nutrition perturbation, plants have difficulty absorbing water from soil because of its elevated osmotic pressure, which leads to water stress and thus complicates and impairs their physiological state in an exponential way. Consequently, cells try to adjust their water potential by ion homeostasis regulation via vacuolar compartmentation and (or) extrusion out of the cell of the toxic ions (Na+ and Cl-). Nevertheless, if this is not sufficient, the plant has to use another way to face salt stress, which consists in the synthesis and accumulation of a class of osmoprotective compounds known as compatible solutes, mainly amino compounds and sugars. Energetically, this osmotic strategy is more expensive than ion homeostasis regulation. A secondary aspect of salinity stress in plants is the stress-induced production of reactive oxygen species leading to an oxidative stress whose damage reduction could be realized via the production of antioxidants. Perception and signal mechanisms represent the first events of plant stress adaptation, and the main pathways followed are calcium, abscissic acid (ABA), mitogen-activated protein kinases (MAPKinases), salt overly sensitive (SOS) proteins, and ethylene.
... However, DNA extracted from dead seeds that were stored for 70 years, mostly under ambient laboratory conditions, had high molecular weight and provided a good template for PCR amplifications of the 650 bp segment coding for the internal transcribed spacer (ITS region) of the nuclear ribosomal RNA gene family (Walters et al. submitted). Most species of seeds are expected to survive for 100 years if stored at -18 ºC (Walters et al. 2005a), and it is expected that viable seeds will yield high quality DNA, although there is some evidence that desiccation and storage induce minor lesions that can be repaired when surviving organisms are rehydrated (Roberts 1988;Phillips et al. 2002;Osborne et al. 2002). ...
... However, most reports of somatic cells show some chromosomal aberrations that are symptomatic of an overall loss in vigour in response to preservation (e.g. Phillips et al. 2002;Osborne et al. 2002). When cells are killed by preservation stresses, enzymes that rapidly degrade DNA are released. ...
... However, DNA extracted from dead seeds that were stored for 70 years, mostly under ambient laboratory conditions, had high molecular weight and provided a good template for PCR amplifications of the 650 bp segment coding for the internal transcribed spacer (ITS region) of the nuclear ribosomal RNA gene family ( Walters et al. submitted). Most species of seeds are expected to survive for 100 years if stored at-18 ºC ( Walters et al. 2005a), and it is expected that viable seeds will yield high quality DNA, although there is some evidence that desiccation and storage induce minor lesions that can be repaired when surviving organisms are rehydrated (Roberts 1988;Phillips et al. 2002;Osborne et al. 2002). ...
... However, most reports of somatic cells show some chromosomal aberrations that are symptomatic of an overall loss in vigour in response to preservation (e.g. Phillips et al. 2002;Osborne et al. 2002). When cells are killed by preservation stresses, enzymes that rapidly degrade DNA are released. ...
... Several desiccation-responsive transcripts from C. plantagineum have been cloned and characterized. However, the molecular signals that lead to their activation are mostly unknown (Phillips, Oliver & Bartels 2002). Some of the genes induced by dehydration in leaves of C. plantagineum share homologies with genes expressed in the seeds of many plant species. ...
... The simultaneous accumulation of specific LEA transcripts and sugars upon drying in C. plantagineum, but not in response to sodium chloride, suggests that both types of molecules must be present in specific concentrations at the same time, and are probably both required for the acquisition of desiccation tolerance. This supports a current hypothesis that LEA proteins act synergistically with non-reducing sugars to form a glassy matrix, in which molecules are embedded and irreversible damage is prevented (Hoekstra et al. 2001;Phillips et al. 2002). Salt-specific responses have been identified through the analysis of salt-sensitive A. thaliana mutants, supporting the existence of ionic stress-specific signalling (Liu & Zhu 1997). ...
Although desiccation tolerant, the resurrection plant Craterostigma plantagineum is sensitive to relatively low levels of sodium chloride. Exposure to sodium chloride, but not dehydration, led to accumulation of sodium ions in leaves and roots and caused irreversible wilting. The effects of salt and dehydration on transcript accumulation patterns were studied by using selected cDNA clones that were related to water stress. Most of the clones represented genes that were up-regulated in response to both treatments. Among the transcripts specifically up-regulated by dehydration were RNAs encoding transcripts with homology to aquaporins. Expression analysis revealed dehydration-specific profiles of late embryogenesis abundant (LEA) genes, which differed from the patterns observed for the same genes under sodium chloride stress. The interconversion of octulose and sucrose, which is characteristic for the desiccation/rehydration cycle in C. plantagineum leaves, was not activated by sodium chloride. The present results suggest that dehydration-specific responses involve the synchronized expression of specific genes and the presence of a determined concentration of sucrose. These dehydration responses were not detected in response to sodium chloride treatment.
... The increase in sugars mostly results in increased starch hydrolysis, which requires activities of hydrolytic enzymes. Resurrection plants and seeds of many higher plants are good examples for a link of carbohydrate (in particular sucrose) accumulation and the acquisition of stress tolerance (Hoekstra et al., 2001;Phillips et al., 2002). This is illustrated with the example of the resurrection plant C. plantagineum, which contains a high amount of the unusual sugar octulose (an 8-carbon sugar), which is rapidly converted into sucrose during dehydration (Bianchi et al., 1991). ...
... A sugar which has been shown to contribute to desiccation tolerance in yeast and some nematodes is trehalose. In higher plants substantial amounts of trehalose were identified in two resurrection plants Myrothamnus flabellifolia and Sporobolus stapfianus (Phillips et al., 2002). It has been reported that many higher plants possess trehalase activity, which is perhaps responsible for rapid degradation of any trehalose synthesized. ...
Agricultural productivity worldwide is subject to increasing environmental constraints, particularly to drought and salinity due to their high magnitude of impact and wide distribution. Traditional breeding programs trying to improve abiotic stress tolerance have had some success, but are limited by the multigenic nature of the trait. Tolerant plants such as Craterostigma plantagenium, Mesembryanthemum crystallinum, Thellungiella halophila and other hardy plants could be valuable tools to dissect the extreme tolerance nature. In the last decade, Arabidopsis thaliana, a genetic model plant, has been extensively used for unravelling the molecular basis of stress tolerance. Arabidopsis also proved to be extremely important for assessing functions for individual stress-associated genes due to the availability of knock-out mutants and its amenability for genetic transformation. In this review, the responses of plants to salt and water stress are described, the regulatory circuits which allow plants to cope with stress are presented, and how the present knowledge can be applied to obtain tolerant plants is discussed.
... Thus, the establishment of genetically tractable bryophyte models that exhibit VDT has been instrumental in understanding the significance of the genomic and molecular innovations that coincided with land plant emergence. Mosses, one of the bryophyte lineages, are excellent model systems for studying VDT (Cove et al., 2009;Rensing et al., 2020;Naramoto et al., 2022;Li et al., 2023;Yadav et al., 2023), particularly as the molecular underpinnings of VDT may be shared across land plants (Phillips et al., 2002;Oliver et al., 2020). The principal bryophyte model that is widely used to study growth and development, Physcomitrium patens (Lang et al., 2018;Rensing et al., 2020), while drought-tolerant (Frank et al., 2005), is generally sensitive to dehydration stress (Mishler & Oliver, 2009;Koster et al., 2010). ...
Water scarcity, resulting from climate change, poses a significant threat to ecosystems. Syntrichia ruralis, a dryland desiccation‐tolerant moss, provides valuable insights into survival of water‐limited conditions.
We sequenced the genome of S. ruralis, conducted transcriptomic analyses, and performed comparative genomic and transcriptomic analyses with existing genomes and transcriptomes, including with the close relative S. caninervis. We took a genetic approach to characterize the role of an S. ruralis transcription factor, identified in transcriptomic analyses, in Arabidopsis thaliana.
The genome was assembled into 12 chromosomes encompassing 21 169 protein‐coding genes. Comparative analysis revealed copy number and transcript abundance differences in known desiccation‐associated gene families, and highlighted genome‐level variation among species that may reflect adaptation to different habitats. A significant number of abscisic acid (ABA)‐responsive genes were found to be negatively regulated by a MYB transcription factor (MYB55) that was upstream of the S. ruralis ortholog of ABA‐insensitive 3 (ABI3). We determined that this conserved MYB transcription factor, uncharacterized in Arabidopsis, acts as a negative regulator of an ABA‐dependent stress response in Arabidopsis.
The new genomic resources from this emerging model moss offer novel insights into how plants regulate their responses to water deprivation.
... The sugars accumulation varied according to the species, the stage of development and the salt concentration and there is a strong correlation between the accumulation of sugars and the level of tolerance to salinity (El Midaoui et al. 2007). The accumulation of sugars, mainly following the hydrolysis of starch (Phillips et al. 2002), is stimulated by salt (Bartels and Sunkar, 2005). Therefore, Urtica pilulifera improved sugar synthesis for osmotic adjustment to avoid salt constraint and to maintain cell survival. ...
Urtica pilulifera from Urticaceae family was known by its benefit effects on human health and used in traditional medicine and recently largely used in pharmacological and food fields. In other hand, the salinization of soils is caused by several environmental factors leading to crop losses around the World. The ability of plants to tolerate salt stress is determined by multiple mechanisms. In the present study, morphological, physiological, and biochemical modulations in Urtica pilulifera under salt stress was evaluated to assess its tolerance or sensitization potential to salt stress using different concentrations of NaCl (0, 50, 100 and 150 mM). The studied parameters of Urtica pilulifera were evaluated by cultivating the plant on a hydroponic medium. Results showed that after 15 days of treatment, a reduction in plant growth was noted correlating with leaf chlorosis under 100 mM NaCl and an increased level of proline and soluble sugar. Regression analysis showed that the applied salt concentration was proportional with the activity of antioxidant enzymes including catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX), both on the arial and the root parts.
Cellular damage induced by salinity is strongly correlated with the generation of reactive oxygen species, osmotic damage, and reduction in relative water content. Accelerated antioxidant activity and osmotic adjustment through training osmolytes, are effective salinity tolerance mechanisms developed by Urtica pilulifera.
... Homology analysis showed that most of the induced orthogroups in tolerant species were also present in the sensitive species. Previous hypotheses suggested that DT evolved from genetic components also present in sensitive plant species [9,[47][48][49], indicating that DT arose by rewiring of regulatory networks rather than the acquisition of novel genes. Evidence of differential regulation between tolerant and sensitive Selaginella species is shown by the expression patterns of PLATZ1, a transcription factor identified as one of the major regulators of seed DT, whose constitutive expression has been demonstrated to increase drought tolerance in vegetative tissues of Arabidopsis [40]. ...
Background
Desiccation tolerant Selaginella species evolved to survive extreme environmental conditions. Studies to determine the mechanisms involved in the acquisition of desiccation tolerance (DT) have focused on only a few Selaginella species. Due to the large diversity in morphology and the wide range of responses to desiccation within the genus, the understanding of the molecular basis of DT in Selaginella species is still limited.
Results
Here we present a reference transcriptome for the desiccation tolerant species S. sellowii and the desiccation sensitive species S. denticulata. The analysis also included transcriptome data for the well-studied S. lepidophylla (desiccation tolerant), in order to identify DT mechanisms that are independent of morphological adaptations. We used a comparative approach to discriminate between DT responses and the common water loss response in Selaginella species. Predicted proteomes show strong homology, but most of the desiccation responsive genes differ between species. Despite such differences, functional analysis revealed that tolerant species with different morphologies employ similar mechanisms to survive desiccation. Significant functions involved in DT and shared by both tolerant species included induction of antioxidant systems, amino acid and secondary metabolism, whereas species-specific responses included cell wall modification and carbohydrate metabolism.
Conclusions
Reference transcriptomes generated in this work represent a valuable resource to study Selaginella biology and plant evolution in relation to DT. Our results provide evidence of convergent evolution of S. sellowii and S. lepidophylla due to the different gene sets that underwent selection to acquire DT
... It was observed that the starch, protein and B concentration was highest in bottom-cold with B. On the other hand, starch accumulation increased in plant in both cold/bottom-cold stress in tomato; the highest glucose was at the cold-air, it seems that under cold-air stress, the starch change to glucose to increase acclimation of plant to cold stress and boron facilitate sugar movement to leaves for improving stress (Waraich et al. 2011;Marschner 1995). It was suggested that the hydrolysis of starch and sugars conversion result in sugars increase (Ingram et al. 1997) leading osmoregulation role of sugar as osmotic to protect some macromolecules and stabilized membrane structures by interact with polar head groups of phospholipids and prevent membrane fusion (Phillips et al. 2002). It has been proved that soluble sugars have a key role in cold acclimation, means that increase in freezing tolerance related to collection of soluble sugars, particularly sucrose (Rutten and Santarius 1992). ...
Boron is beneficial element can help plants face chilling stress. This research was arranged using factorial experiment based on randomized complete block design on Lycopersicon esculentum var. Infinity in Isfahan University of Technology due to having a new idea about bottom-cold and cold-air stress tomato seedling with boron application. There were two treatments having different boron (B1) concentrations (B1) 50.5 mM, and (B2) 75.82 mM. Three temperature treatment used as following: (1) the cold treatment used with vegetation chambers with low temperature (10 °C) (cold air), (2) the low nutrient solution (10 °C) temperature but the aerial part exposed to optimum temperature (bottom-cold) and (3) the last part, was the control plant (opt) keep in optimum root and shoot temperature (22 °C). Some physiological and biochemical characteristics were measured. The results were shown that boron uptake decreased in cold or stress as well as the water status of the plant which is suffering from cold-air stress greater than bottom-cold. Boron application, especially in higher concentration, improved some deleterious effect of cold stress, especially in the bottom-cold. The reason may refer to keeping photosynthesis traits in better level with B application. Cold-air stress, increased stress indices such as antioxidant and proline as well as glucose level and saturated/unsaturated fatty acid greater than bottom-cold stress. It was concluded that tomato was more resistant to bottom-cold stress than cold-air stress. Boron application increased the boron of leaves more effectively in the bottom-cold consequently increase plant tolerance to a chilling condition at the bottom-cold too.
... Several physiological studies have shown that the accumulation of sugars and polyols, mainly following hydrolysis of starch], was stimulated by salt stress in different plant species [22][23][24][25][26][27][28]. ...
... Em plântulas de cajueiro anão precoce, submetidas à salinidade não foram verificadas diferenças significativas na concentração de carboidratos em folhas e raízes de plântulas (Abreu et al. 2008 indicar um ajuste para proteção e tolerância das plântulas à restrição hídrica e maior acúmulo de íons (Na + e Cl -), por meio do acúmulo de osmólitos e aumento da atividade de enzimas antioxidantes . As plantas recuperadas do estresse e as sementes de muitas plantas superiores são bons exemplos da ligação entre o acúmulo de carboidratos (sacarose em particular) e a aquisição da tolerância ao estresse (Hoekstra et al. 2001, Phillips et al. 2002. Esse desvio do metabolismo pode explicar também as menores medidas de crescimento encontradas nessas CEs (Figura 1). ...
O objetivo deste trabalho foi avaliar o efeito do estresse salino sobre o crescimento plântulas de Erythrina velutina Willd. (Fabaceae). As sementes de mulungu foram colocadas para germinar em solução de NaCl preparada em diferentes condutividades elétricas (CE): 0, 4, 6, 8 e 12 dS.m-1, durante 16 dias. Além do número de sementes germinadas (%), foram analisadas: comprimento, a massa fresca e seca da parte aérea e da raiz primária das plântulas. A massa seca da parte aérea e raiz foi posteriormente utilizada para extração e quantificação dos açúcares solúveis totais (AST); açúcares redutores (AR); sacarose (SAC); proteínas solúveis (PT) e aminoácidos totais (AA). A germinação das sementes de E. velutina não foi afetada pelo tratamento de simulação de estresse salino e o crescimento de plântulas foi afetado negativamente após 16 dias de estresse. Soluções de maior CE foram capazes de reduzir a produção de massa seca proporcionando diminuição da razão parte aérea/raiz de E. velutina. A restrição hídrica promovida pelo sal provocou uma desaceleração dos processos fisiológicos e bioquímicos durante a germinação. Esta espécie provavelmente não suporta crescer em solos com potencial osmotico superior a 6 dS.m-1 CE.
... Furthermore, the increase of sugar concentrations is a result of the starch hydrolysis which needs intense hydrolytic enzyme activities. The recovery of stressed plants and seeds of several higher plants are examples of the accumulation of carbon compounds as strategy to tolerate the water deficit (Hoekstra, 2001;Phillips, 2002). Compatible osmolytes are potent osmoprotectants that play role in counteracting the effects of osmotic stress. ...
Sugarcane being a C4 crop produces a large amount of biomass is a water-loving crop, its requirements
for water and fertilizers are equally very high. Water is already a scarce commodity in many parts of
the world and predicted climate changes will aggravate the situation in future. Due to glycophytic
nature of this crop, drought conditions interfere with sugar production by affecting growth rate, yield
of the cane, juices of lower sucrose contents and the sucrose content of the stalk. Thus, drought may
reduce sugarcane yield up to 50% or even more being a multi-dimensional stress, it causes various
physiological and biochemical effects on plants. Enhancing the tolerance of this crop to abiotic stresses
such as drought has therefore proved to be somewhat elusive in terms of plant breeding. Researchers
are looking for different agronomic and physiological traits, which could lead to adaptation to these
conditions or be correlated to drought tolerance. This article is an attempt to put emphasis on some
potential strategies like physiological, biochemical and biotechnological that could be used in breeding
for development of superior sugarcane varieties that improve crop productivity in water stress
environments.
... Bartels and Salamini (2001) concluded that the basic patterns of changes in gene expression that occur in response to dehydration can be summarized for Craterostigma plantagineum as follows: (i) some transcripts accumulate to high levels during dehydration, and disappear early during rehydration; (ii) some transcripts accumulate transiently during the initial dehydration phase; (iii) some transcripts decline during dehydration; and (d) some transcripts remain unchanged in response to dehydration. Studies of tissue-specific expression patterns and subcellular localization have revealed specific cellular distributions of RNAs and proteins that appear to correlate with their predicted functions (Phillips et al., 2002). ...
Dehydration survival under drought stress is defined in this review as the transition from plant activity into a quiescent state of life preservation, which will be terminated by either recovery or death, depending on the stress regime and the plant's resilience. Dehydration survival is a popular phenotype by which functional genomics attempts to test gene function in drought resistance and survival. The available reports on phenotyping and genotyping of dehydration survival in genomic studies indicate that the measurement of this trait is often biased to the extent that misguided interpretations are likely to occur. This review briefly discusses the physiological basis of dehydration survival in resurrection plants and crop plants, and concludes that in phenotyping dehydration survival there is a need to distinguish between dehydration avoidance and dehydration tolerance (also termed desiccation tolerance) in affecting survival and recovery. Without this distinction, functional genomics studies of the trait might be biased. Survival due to dehydration avoidance is expressed by the capacity to maintain a relatively high plant water status as the plant is desiccated. Survival due to dehydration tolerance is expressed by delayed mortality (mortality at a relatively low plant water status) as affected by the resilience of plant metabolism. The common test of dehydration survival, using the relative recovery after a given number of stress days, is therefore insufficient because it is mainly driven by dehydration avoidance and so ignores a possible role for dehydration tolerance. Conceivable methods for more accurate phenotyping of the two components of dehydration survival are proposed and discussed.
... Em plântulas de cajueiro anão precoce, submetidas à salinidade não foram verificadas diferenças significativas na concentração de carboidratos em folhas e raízes de plântulas (Abreu et al. 2008 indicar um ajuste para proteção e tolerância das plântulas à restrição hídrica e maior acúmulo de íons (Na + e Cl -), por meio do acúmulo de osmólitos e aumento da atividade de enzimas antioxidantes . As plantas recuperadas do estresse e as sementes de muitas plantas superiores são bons exemplos da ligação entre o acúmulo de carboidratos (sacarose em particular) e a aquisição da tolerância ao estresse (Hoekstra et al. 2001, Phillips et al. 2002. Esse desvio do metabolismo pode explicar também as menores medidas de crescimento encontradas nessas CEs (Figura 1). ...
Recebido em 05 de janeiro de 2017. Aceito em 30 de julho de 2017. Publicado em 30 de dezembro de 2017. rEsumo-O objetivo deste trabalho foi avaliar o efeito do estresse salino sobre o crescimento plântulas de Erythrina velutina Willd. (Fabaceae). As sementes de mulungu foram colocadas para germinar em solução de NaCl preparada em diferentes condutividades elétricas (CE): 0, 4, 6, 8 e 12 dS.m-1 , durante 16 dias. Além do número de sementes germinadas (%), foram analisadas: comprimento, a massa fresca e seca da parte aérea e da raiz primária das plântulas. A massa seca da parte aérea e raiz foi posteriormente utilizada para extração e quantificação dos açúcares solúveis totais (AST); açúcares redutores (AR); sacarose (SAC); proteínas solúveis (PT) e aminoácidos totais (AA). A germinação das sementes de E. velutina não foi afetada pelo tratamento de simulação de estresse salino e o crescimento de plântulas foi afetado negativamente após 16 dias de estresse. Soluções de maior CE foram capazes de reduzir a produção de massa seca proporcionando diminuição da razão parte aérea/raiz de E. velutina. A restrição hídrica promovida pelo sal provocou uma desaceleração dos processos fisiológicos e bioquímicos durante a germinação. Esta espécie provavelmente não suporta crescer em solos com potencial osmotico superior a 6 dS.m-1 CE. palavras chavE: Caatinga; MaCroMoléCulas; salinidadE; vigor. EffEct of salt strEss on gErmination and initial groWth of Erythrina vElutina Willd. (fabacEaE) sEEdlings abstract-The objective of this study was to evaluate the effect of salinity on growth of Erythrina velutina Willd. (Fabaceae) seedlings. Mulungu seeds were germinated in NaCl solution prepared in different electrical conductivity (EC): 0, 4, 6, 8 and 12dS.m-1 for 16 days. Besides the number of germinated seeds (%), were analyzed: total length, fresh and dry weight of shoot and primary root. The dry weight of shoot and root was subsequently used for extraction and quantification of soluble sugars (AST), sugars (RS), sucrose (SAC), soluble proteins (TP) and total amino acids (AA). The germination of mulungu was not affected by simulation of salt stress, differently from results of seedlings development. Solutions of higher EC were able to reduce the production of dry mass providing lower shoot/root of E. velutina seedlings. The water restriction promoted by salt caused a slowing of physiological and biochemical processes during germination. This specie probably does not support grow on osmotic potential exceeding 6 dS.m-1. EfEcto dEl Estrés salino En la gErminación y En El crEcimiEnto inicial dE plántulas dE Erythrina vElutina Willd. (fabacEaE)
... Osmotic adjustment in order to maintain cells osmotic potential, is a key mechanism to face osmotic stress caused by drought, particularly when drought stress rises gradually (Lipiec et al., 2013). In many cases, it has been reported that there is strong correlation between sugars, trehalose accumulation and drought tolerance in plant species (Bartels & Sunkar, 2005;Phillips et al., 2002). In our study, the pattern of changes regarding TSS and trehalose content in response to increasing water deficit (regardless priming treatments) was almost similar to GB and proline, yet the reaction to priming treatments especially with SA, was totally different between them. ...
Due to low rainfall at early autumn, smooth vetch seedling growth in rain-fed lands often is limited by water deficit stress yet the data regarding the reactions of smooth vetch to water deficit at early growth stages are pretty rare. The objective of current study was to examine possibility of using priming treatments (hydro priming and priming salicylic acid) to alleviate the inhibitory effect of water deficiency during early growth of Smooth Vetch. In this respect, seeds were soaked in distilled water (hydro priming) or 0.5 mM solution of SA for 36 h at 10 °C then dried back to original moisture content. Pots were irrigated for 25 days at four levels of available water containing field capacity (FC), 75% FC, 50% FC and 25% FC. In general, seedling emergence and early growth were markedly limited by increasing water deficiency. However, priming treatments particularly with SA caused considerable improvement in either emergence or growth of seedlings (dry weight, length). The obtained results showed that primed samples exhibited higher accumulation of proline, glycine betaine (GB) under all levels of available water except 100% FC and also higher total soluble sugars (TSS) and trehalose under severe water deficit (25% FC). SA primed samples had higher relative water content especially under higher levels of water deficiency. The more balanced water status within SA primed samples also was accompanied with higher accumulation of proline and glycine betaine. There were significant differences between two priming treatments in terms of proline and GB content within seedlings and SA priming considerably increased proline and GB accumulation. In contrast to proline and GB, TSS and trehalose content wasn’t influenced by SA treatment and both hydro and SA primed samples showed statistically similar quantities.
... Although it has not been tested specifically under field conditions, it restricts the use of selected EPN populations to favorable temperature regimes. Desiccation tolerance is the ability to survive dehydration stress via reversible cessation of metabolism (Phillips et al., 2002) and it is essential for survival and persistence under dry conditions (Glazer, 2015). The enhanced desiccation tolerance of the selected populations of S. carpocapsae (1.2-to 1.4-fold) and H. bacteriophora (1.4-to 1.7-fold) denotes their better fitness to withstand desiccation stress. ...
Rhynchophorus ferrugineus (red palm weevil) is highly susceptible to infection by the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora. However, to reach and penetrate the insect in its habitat with good efficacy, the nematode infective juveniles (IJs) need to move through the tunnels bored by the feeding insect larvae in the tree trunk. We used a genetic-improvement approach to enhance host-seeking ability (HSA) of these nematode species’ IJs. The IJs were allowed to move through a 45-cm L-shaped tube toward red palm weevil larvae. The IJs which reached within 5 cm of the insect larvae were collected and reared. Selection cycles were repeated 15 times. The HSA of S. carpocapsae IJs was enhanced 11-fold (from 3.7 to 39.8% of all IJs reaching proximity of the larvae) and 8.5-fold (from 2.3 to 19.7%) for H. bacteriophora after 10 cycles of selection. Further selections (cycles 11 to 15) had no significant impact on improving HSA. HSA of the selected lines was highly specific to R. ferrugineus larvae. Selection for improved HSA also enhanced infectivity to R. ferrugineus, Galleria mellonella and Spodoptera littoralis. In addition, it enhanced host penetration 2.7-fold for S. carpocapsae and 1.5-fold for H. bacteriophora, and desiccation tolerance improved 1.2- and 1.7-fold, respectively. Heat tolerance and fecundity of the selected lines were somewhat reduced (MT50 by factors of 1.02 and 1.2 and fecundity by factors of 0.93 and 0.99, respectively) as compared to the foundation population. Improved HSA with substantial improvement of other traits may enhance field performance of these biocontrol agents.
... Desiccation tolerant organisms are able to dehydrate to water content below 0.1 g(H 2 O) g -1 (d.m.), rehydrate, and resume normal growth (Oliver et al. 2000, Phillips et al. 2002. Ability to tolerate desiccation is common feature of angiosperm seeds (orthodox seeds; Potts 1994, Dinakar andBartels 2013). ...
Desiccation tolerance (DT) is the ability to tolerate dehydration to levels below 0.1 g(H2O) g-1(dry mass) and subsequent rehydration without lethal damage. Here, it is proposed that Leucaena leucocephala, a tree species, has potential to be model tolerant species in seed research. Using flow cytometry and transmission electron microscopy, cytological changes related to loss of DT in Leucaena primary roots were followed during germination. Leucaena seeds lost their DT at the end of germination and this coincided with an increase in cellular 4C DNA content. A negative correlation between the 8C DNA content and the capacity of germinating Leucaena seeds to tolerate desiccation was also observed. Apparently, the seeds of Leucaena underwent extra cycles of endoreduplication and accumulated a high content of DNA–an event not previously linked to DT. The ultrastructural damage imposed by drying overcame Leucaena primary root cell resilience and their ability to resume normal growth. Nuclear DNA content may be used as indicator of progress of germination and loss of DT in Leucaena.
... A variety of recovery measures suggest this 12-24 h timeline, including oxygen consumption (as returning to control levels and dependent upon prior rate of drying; , carbon balance (cf. Tuba et al., 1996 andReed et al., 2012, who found C balance to recover in $60 min in Syntrichia; Schonbeck and Bewley, 1981a;Oechel, 1985, 1987;Proctor and Pence, 2002;Proctor et al., 2007b; noting that time to positive carbon balance depends upon the duration of the dry period and the equilibrating RH; Hinshiri and Proctor, 1971;Dilks and Proctor, 1974), resumption of control levels of protein synthesis (Oliver, 1991), cellular integrity (Bewley et al., 1993), return to normal appearance of organelles (Bewley and Pacey, 1978;Phillips et al., 2002;Proctor et al., 2007b), chlorophyll fluorescence (Hellwege et al., 1994;Proctor and Pence, 2002;Schlensog et al., 2004;Proctor et al., 2007b;Pressel et al., 2009), vacuole recovery (Proctor et al., 2007b) and cytoskeleton recovery (Pressel et al., 2006). The treatment of plants prior to testing for recovery and the inherent ecological strategy employed by the species under study should each heavily influence results for estimates of recovery, with deacclimated plants expected to segregate into longer recovery (IDT) and shorter/no recovery (CDT) times. ...
Background and aims:
Embryonic sporophytes of the moss Aloina ambigua are inducibly desiccation tolerant (DT). Hardening to DT describes a condition of temporary tolerance to a rapid-drying event conferred by a previous slow-drying event. This paper aimed to determine whether sporophytic embryos of a moss can be hardened to DT, to assess how the rate of desiccation influences the post-rehydration dynamics of recovery, hardening and dehardening, and to determine the minimum rate of drying for embryos and shoots.
Methods:
Embryos were exposed to a range of drying rates using wetted filter paper in enclosed Petri dishes, monitoring relative humidity (RH) inside the dish and equilibrating tissues with 50 % RH. Rehydrated embryos and shoots were subjected to a rapid-drying event at intervals, allowing assessments of recovery, hardening and dehardening times.
Key results:
The minimum rate of slow drying for embryonic survival was ∼3·5 h and for shoots ∼9 h. Hardening to DT was dependent upon the prior rate of drying. When the rate of drying was extended to 22 h, embryonic hardening was strong (>50 % survival) with survival directly proportional to the post-rehydration interval preceding rapid drying. The recovery time (repair/reassembly) was so short as to be undetectable in embryos and shoots desiccated gradually; however, embryos dried in <3·5 h exhibited a lag time in development of ∼4 d, consistent with recovery. Dehardening resulted in embryos incapable of surviving a rapid-drying event.
Conclusions:
The ability of moss embryos to harden to DT and the influence of prior rate of drying on the dynamics of hardening are shown for the first time. The minimum rate of drying is introduced as a new metric for assessing ecological DT, defined as the minimum duration at sub-turgor during a drying event in which upon rehydration the plant organ of interest survives relatively undamaged from the desiccating event.
... A signi fi cant amount of trehalose has been found in two resurrection plants Myrothamnus fl abellifolia and Sporobolus stap fi anus (Phillips et al. 2002 ) where trehalose is thought to prevent intracellular structural damage due to anhydrobiosis (Lunn 2007 ) . ...
Abiotic stresses such as drought, cold, heat, and salinity are major factors that limit plant growth and development and account for a major loss in crop productivity worldwide. Thus, engineering plants for tolerance towards such environmental menaces is the prime concern for crop improvement programs. Engineering osmoprotectants biosynthetic pathway is considered as one among many successful approaches taken for crop improvement under adverse conditions. Osmoprotectants or compatible solutes are thought to act by stabilizing membranes and proteins and maintaining osmotic potential in the cell during stresses. Although not all crop plants are able to synthesize these special molecules, many stress tolerant plants are shown to accumulate them under stress conditions. This group primarily includes proline, glycine betaines, ectoine, trehalose, and polyols. However, many attempts have been made at engineering plant system with genes from biosynthetic pathways of osmoprotectants; these transgenic plants have shown different tolerance levels, because of many metabolic limitations. Thus, a more elaborate and wholesome approach may be required to look past the current scenario. This chapter will encompass the potential role of osmoprotectants in plant stress adaptation and the possibilities for crop improvement.
... This diversity reflects the adaptability of inhabitants at physiological, biochemical and genetic levels to cope with the prevailing environment. Occupying extreme environmental niche, certain organisms can survive removal of almost all of their cellular water without irreversible damage; such organisms are referred to as desiccation tolerant or anhydrobiotes1234 and the phenomenon itself as anhydrobiosis . Measurements of water potential by Gaff group indicated that even when plants are equilibrated at 50% relative humidity at 28 @BULLET C, they experience a water deficit equivalent to that of −100 MPa pressure which is lethal for the majority of angiosperms [5]. ...
Programmed cell death (PCD) is an integral cellular program by which targeted cells culminate to demise under certain developmental and pathological conditions. It is essential for controlling cell number, removing unwanted diseased or damaged cells and maintaining the cellular homeostasis. The details of PCD process has been very well elucidated and characterised in animals but similar understanding of the process in plants has not been achieved rather the field is still in its infancy that sees some sporadic reports every now and then. The plants have two energy generating sub-cellular organelles- mitochondria and chloroplasts unlike animals that just have mitochondria. The presence of chloroplast as an additional energy transducing and ROS generating compartment in a plant cell inclines to advocate the involvement of chloroplasts in PCD execution process. As chloroplasts are supposed to be progenies of unicellular photosynthetic organisms that evolved as a result of endosymbiosis, the possibility of retaining some of the components involved in bacterial PCD by chloroplasts cannot be ruled out. Despite several excellent reviews on PCD in plants, there is a void on an update of information at a place on the regulation of PCD by chloroplast. This review has been written to provide an update on the information supporting the involvement of chloroplast in PCD process and the possible future course of the field.
... This diversity reflects the adaptability of inhabitants at physiological, biochemical and genetic levels to cope with the prevailing environment. Occupying extreme environmental niche, certain organisms can survive removal of almost all of their cellular water without irreversible damage; such organisms are referred to as desiccation tolerant or anhydrobiotes [1][2][3][4] and the phenomenon itself as anhydrobiosis. Measurements of water potential by Gaff group indicated that even when plants are equilibrated at 50% relative humidity at 28 • C, they experience a water deficit equivalent to that of −100 MPa pressure which is lethal for the majority of angiosperms [5]. ...
Anhydrobiosis is an adaptive strategy of certain organisms or specialised propagules to survive in the absence of water while programmed cell death (PCD) is a finely tuned cellular process of the selective elimination of targeted cell during developmental programme and perturbed biotic and abiotic conditions. Particularly during water stress both the strategies serve single purpose i.e., survival indicating PCD may also function as an adaptive process under certain conditions. During stress conditions PCD cause targeted cells death in order to keep the homeostatic balance required for the organism survival, whereas anhydrobiosis suspends cellular metabolic functions mimicking a state similar to death until reestablishment of the favourable conditions. Anhydrobiosis is commonly observed among organisms that have ability to revive their metabolism on rehydration after removal of all or almost all cellular water without damage. This feature is widely represented in terrestrial cyanobacteria and bryophytes where it is very common in both vegetative and reproductive stages of life-cycle. In the course of evolution, with the development of advanced vascular system in higher plants, anhydrobiosis was gradually lost from the vegetative phase of life-cycle. Though it is retained in resurrection plants that primarily belong to thallophytes and a small group of vascular angiosperm, it can be mostly found restricted in orthodox seeds of higher plants. On the contrary, PCD is a common process in all eukaryotes from unicellular to multicellular organisms including higher plants and mammals. In this review we discuss physiological and biochemical commonalities and differences between anhydrobiosis and PCD.
... Previous research showed that the accumulation of compatible solutes such as sugars may protect plants against stress environments [50], and nonstructural carbohydrates (sucrose, hexoses, and sugar alcohols) were found to have a strong correlation between sugar accumulation and osmotic stress tolerance [47]. It was suggested that sugars act as osmotica and contribute to the stabilization of membrane structures, protecting cells during desiccation [51], and interact with polar headgroups of phospholipids in cell membranes to prevent membrane fusion. Our experiment showed higher seed stachyose accumulation under water stress, reflecting possible role in drought stress, supporting previous findings [47]. ...
Therefore, the objective of the current research was to investigate the effects of foliar B nutrition on seed protein, oil, fatty acids, and sugars under water stress conditions. A repeated greenhouse experiment was conducted using different maturity group (MG) cultivars. Plants were well-watered with no foliar B (W − B), well-watered with foliar B (W + B), water-stressed with no foliar B (WS − B), and water-stressed with foliar B (WS + B). Foliar B was applied at rate of 0.45 kg·ha−1 and was applied twice at flowering and at seed-fill stages. The results showed that seed protein, sucrose, fructose, and glucose were higher in W + B treatment than in W − B, WS + B, and WS − B. The increase in protein in W + B resulted in lower seed oil, and the increase of oleic in WS − B or WS + B resulted in lower linolenic acid. Foliar B resulted in higher nitrogen fixation and water stress resulted in seed δ
15N and δ
13C alteration. Increased stachyose indicated possible physiological and metabolic changes in carbon and nitrogen pathways and their sources under water stress. This research is beneficial to growers for fertilizer management and seed quality and to breeders to use 15N/14N and 13C/12C ratios and stachyose to select for drought tolerance soybean.
... Desiccation tolerance is a complex phenomenon and the understanding of the protection mechanisms involved in the drying and the resurrection process is still patchy. Excellent reviews have been recently published on the molecular, signalling and regulatory aspects of desiccation tolerance (Hoekstra, Golovina & Buitink 2001; Phillips, Oliver & Bartels 2002; Ramanjulu & Bartels 2002; Mundree et al . 2002). ...
The cell wall architecture of leaf tissues of the resurrection plant Craterostigma wilmsii at various stages of dehydration and rehydration was studied using electron microscopy and immunocytochemistry with antibodies to a hemicellulose (xyloglucan) and pectins. Upon dehydration, the cell walls were shown to fold extensively. It is thought that this folding may prevent excessive mechanical stress developing between the cell wall and the plasmalemma. Our immunocytochemical results show a significant increase in labelling of xyloglucan and unesterified pectins in the cell wall during drying, with levels declining again during rehydration. These components are known to play an important structural role within the cell wall, giving it more tensile strength. It is hypothesised that this increase in tensile strength allows the cell wall to contract and then fold as the plant dries and ultimately prevents the total inward collapse of the cell walls in dry tissue. The increased tensile strength may also be necessary to prevent the cell wall from unfolding and expanding too rapidly upon rehydration, thus allowing plasmalemma-cell wall connections to be reestablished.
... It was suggested that the increase in sugars was a result of starch hydrolysis and sugars conversion (Ingram et al., 1997). Also, it was hypothesized that sugars act as osmotica and/or protect specific macromolecules and contribute to the stabilization of membrane structures, protect cells during desiccation (Phillips et al., 2002), and interact with polar headgroups of phospholipids in cell membranes to prevent membrane fusion. In our experiment, stachyose accumulation occurred under water stress, and this in agreement with other reports that many seeds accumulate considerable amounts of raffinoase oligosaccharides (RFOs) such as raffinose and stachyose. ...
Cited By (since 1996):2, Export Date: 18 October 2014
... One function may protect the cell via glass formation [20], a liquid with the mechanical properties of a solid. Secondly, sucrose may maintain hydrogen bonds within and between macromolecules and maintain the structure [21]. H. caudiculatum fronds showed no significant differences between hydrated (137 AE 9 mmol g À1 DW) and desiccated (129 AE 39 mmol g À1 DW) states, and a decrease in rehydrated (66 AE 9 mmol g À1 DW) fronds. ...
The Hymenophyllaceae is a primitive family within the Filicopsidae. One of the most exceptional features of this family of ferns is the presence of fronds with one or just a few cell layers (hence their name of filmy ferns), and the absence of stomata. Hymenophyllum caudiculatum and Hymenophyllum dentatum are able to lose more than 82% of their fully hydrated water content, to remain dry for extended periods of time (days or weeks), and to survive and remain viable following rehydration. The aim of this work was to understand whether the adaptive strategy of the Hymenophyllaceae for desiccation tolerance is constitutive or inducible. A proteomic approach was adopted in combination with physiological parameters to assess whether there were changes in the protein content during dehydration and following rehydration. Detached fronds were used to monitor the rates of photosynthesis in desiccation experiments, sugar accumulation, and high-resolution 2-DE to analyze proteome variation during a desiccation-rehydration cycle. The analyzed proteome exhibited little variation (3-4%) between hydrated and desiccated states, while variation was greater between the desiccated and rehydrated states (8.7-10%). Eighty-two discrete proteins were analyzed by MS/MS, and 65 were identified. About 21% of the analyzed proteins (17) were mixtures of two or more different polypeptides. Of the identified proteins, more than a half (33 spots, 55%) had functions related to energy-photosynthesis. The second largest category with known function (five spots, 8%) was related to cell rescue, defense, and virulence. More than one in every four proteins analyzed belonged to a group of hypothetical proteins (18 spots, 28%). The results suggest that the Hymenophyllaceae represent an example of a change in adaptive strategy from a typical vascular to the poikilohydric homoiochlorophyllous adaptation, which they share with the bryophytes that grow in profusion in the same habitats. The speed at which desiccation takes place therefore precludes the induction of protective systems, suggesting a constitutive mechanism of cellular protection.
... One function may protect the cell via glass formation [20], a liquid with the mechanical properties of a solid. Secondly, sucrose may maintain hydrogen bonds within and between macromolecules and maintain the structure [21]. H. caudiculatum fronds showed no significant differences between hydrated (137 AE 9 mmol g À1 DW) and desiccated (129 AE 39 mmol g À1 DW) states, and a decrease in rehydrated (66 AE 9 mmol g À1 DW) fronds. ...
The Hymenophyllaceae Link is a primitive family within the Filicopsidae. One of the most
outstanding features of this family of ferns is the presence of fronds with one or few cell
layers (hence their name of filmy ferns) and therefore the absence of stomata.
Hymenophyllum caudiculatum and Hymenophyllum dentatum are able to lose more than
82% of their water content, remain dry for some time (days or weeks) and survive upon
rehydration. The aim of this work was to understand if the adaptative strategy of
Hymenophyllacea for desiccation tolerance is constitutive or inducible. A proteomic
approach has been adopted in combination with physiological parameters. Detached fronds
were used to monitor photosynthesis recovery in desiccation experiments, total sugar
content to measure compatible solutes accumulation, and high resolution 2-DE to analyze
proteome variation during a desiccation-rehydration cycle. The analyzed proteome showed
a variation of 3-4% between hydrated and desiccated states and 8.7-10% between
desiccated and rehydrated. 82 proteins were analyzed by MS/MS and 65 identified, 17
spots were mixed. Of the identified proteins 33 spots (55%) correspond to Energy-
Photosynthesis, 18 spots (28%) to hypothetical proteins and 5 spots (8%) to cell rescue,
defense and virulence.
Hymenophyllaceas are an example of a change in adaptative strategy from a typical
vascular to the poikilohydric homoiochlorophyllous adaptation which they share with the
bryophytes that grow in profusion in the same habitats. The speed at which desiccation
takes place precludes the induction of protective systems suggesting a constitutive
mechanism of cellular protection.
... For example, it was reported that the accumulation of compatible solutes such as sugars (non-structural sugars), including sucrose, raffinose, stachyose (Chen and Murata, 2002), and sucrose, hexoses, and sugar alcohols accumulation are related to osmotic stress tolerance (Streeter et al., 2001;Taji et al., 2002). It was explained that the accumulation of sugars was a result of starch hydrolysis and sugars conversion (Ingram et al., 1997), where sugars act as osmotica to protect specific macromolecules and stabilize membrane structures, protect cells during desiccation (Phillips et al., 2002), and prevent membrane fusion. In our experiment, the accumulation of raffinose oligosaccharides (RFOs) was higher in SLW genotypes than in check genotypes under drought stress, and this is in agreement with other reports that many seeds accumulate considerable amounts of RFOs such as raffinose and stachyose under drought stress. ...
Recent advances in soybean breeding have resulted in genotypes that express the slow-wilting phenotype (trait) under drought stress conditions. The physiological mechanisms of this trait remain unknown due to the complexity of trait × environment interactions. The objective of this research was to investigate nitrogen metabolism and leaf and seed nutrients composition of the slow-wilting soybean genotypes under drought stress conditions. A repeated greenhouse experiment was conducted using check genotypes: NC-Roy (fast wilting), Boggs (intermediate in wilting); and NTCPR94-5157 and N04-9646 (slow-wilting, SLW) genotypes. Plants were either well-watered or drought stressed. Results showed that under well-watered conditions, nitrogen fixation (NF), nitrogen assimilation (NA), and leaf and seed composition differed between genotypes. Under drought stress, NF and NA were higher in NTCPR94-5157 and N04-9646 than in NC-Roy and Boggs. Under severe water stress, however, NA was low in all genotypes. Leaf water potential was significantly lower in checks (−2.00 MPa) than in the SLW genotypes (−1.68 MPa). Leaf and seed concentrations of K, P, Ca, Cu, Na, B were higher in SLW genotypes than in the checks under drought stress conditions. Seed protein, oleic acid, and sugars were higher in SLW genotypes, and oil, linoleic and linolenic acids were lower in SLW genotypes. This research demonstrated that K, P, Ca, Cu, Na, and B may be involved in SLW trait by maintaining homeostasis and osmotic regulation. Maintaining higher leaf water potential in NTCPR94-5157 and N04-9646 under drought stress could be a possible water conservation mechanism to maintain leaf turgor pressure. The increase in osmoregulators such as minerals, raffinose, and stachyose, and oleic acid could be beneficial for soybean breeders in selecting for drought stress tolerance.
... It was suggested that the increase in sugars was a result of starch hydrolysis and sugars conversion (Ingram et al., 1997). Also, it was hypothesized that sugars act as osmotica and/or protect specific macromolecules and contribute to the stabilization of membrane structures, protect cells during desiccation (Phillips et al., 2002), and interact with polar headgroups of phospholipids in cell membranes to prevent membrane fusion. In our experiment, stachyose accumulation occurred under water stress, and this in agreement with other reports that many seeds accumulate considerable amounts of raffinoase oligosaccharides (RFOs) such as raffinose and stachyose. ...
Limited information is available on the effects of foliar boron (B) application on soybean seed composition. The objective of this research was to investigate the effects of foliar B on seed composition (protein, oil, fatty acids, and sugars). Our hypothesis was that since B is involved in nitrogen and carbon metabolism, it may impact seed composition. A repeated greenhouse experiment was conducted where half of the soybean plants was exposed to water stress (WS) and the other half was well-watered. Foliar boron (FB) in the form of boric acid was applied twice at a rate of 1.1 kg ha⁻¹. The first application was during flowering stage, and the second application was during seed-fill stage. Treatments were water stressed plants with no FB (WS–B); water stressed plants with FB (WS+B); watered plants without FB (W–B), and watered plants with FB (W+B). The treatment W–B was used as a control. Comparing with WS–B plants, B concentration was the highest in leaves and seed of W+B plants (84% increase in leaves and 73% in seed). Seeds of W+B plants had higher protein (11% increase), oleic acid (27% increase), sucrose (up to 40% increase), glucose, and fructose comparing with W–B. However, seed stachyose concentrations increased by 43% in WS–B plants seed compared with W–B plants. Cell wall (structural) B concentration in leaves was higher in all plants under water stress, especially in WS–B plants where the percentage of cell wall B reached up to 90%. Water stress changed seed δ¹⁵N and δ¹³C values in both B applied and non-B applied plants, indicating possible effects on nitrogen and carbon metabolism. This research demonstrated that FB increased B accumulation in leaves and seed, and altered seed composition of well-watered and water stressed plants, indicating a possible involvement of B in seed protein, and oleic and linolenic fatty acids. Further research is needed to explain mechanisms of B involvement in seed protein and fatty acids.
... Studies aimed at elucidating the suite of physiological, molecular, genetic and biochemical mechanisms of vegetative DT have focused upon four plant models: Craterostigma plantagineum (an African Scrophulariaceae), Sporobolus stapfianus (an African grass), species of the African Velloziaceae genus Xerophyta (Collet et al. 2004;Dace et al. 1998;Mowla et al. 2002), and the moss Tortula ruralis (Wood & Oliver 2004). The proposed mechanisms of DT differ between mosses and angiosperms (Alpert & Oliver 2002;Phillips et al. 2002). Resurrection plants, such as C. plantagineum, employ an inducible cellular protection mechanism, which relies in part on a drying-induced accumulation of abscisic acid (ABA) (Bartels & Sunkar 2005). ...
Desiccation-tolerance is the unique ability to revive from the air-dried state. In this review, I summarize the distribution of vegetative desiccation-tolerance within the land plants emphasizing bryophytes, and provide a current checklist of those moss, liverwort and hornwort species with documented and experimentally determined tolerance. Desiccation-tolerant species can survive equilibration with either modestly dry air (i.e., 70–80% RH or −30 to −48 MPa) or extremely dry air (i.e., 0–30% RH or less than −162 MPa), and have been identified within seven classes of bryophytes, the Andreaeopsida, Bryopsida, Polytrichopsida and Tetraphidopsida (mosses), Jungermanniopsida and Marchantiopsida (liverworts) and the Anthocerotopsida (hornworts); 210 out of 21,000 bryophyte species (ca. 1.0%) have been experimentally determined to possess vegetative desiccation tolerance—158 species of mosses, 51 species of liverworts and one species of hornwort. Finally, I propose a comprehensive survey of mosses, liverworts and hornworts using a standard procedure that employs modulated chlorophyll fluorescence for analyzing vegetative desiccation-tolerance (i.e., the “Austin Protocol”).
... Studies aimed at elucidating the suite of physiological, molecular, genetic and biochemical mechanisms of vegetative DT have focused upon four plant models: Craterostigma plantagineum (an African Scrophulariaceae), Sporobolus stapfianus (an African grass), species of the African Velloziaceae genus Xerophyta (Collet et al. 2004;Dace et al. 1998;Mowla et al. 2002), and the moss Tortula ruralis (Wood & Oliver 2004). The proposed mechanisms of DT differ between mosses and angiosperms (Alpert & Oliver 2002;Phillips et al. 2002). Resurrection plants, such as C. plantagineum, employ an inducible cellular protection mechanism, which relies in part on a drying-induced accumulation of abscisic acid (ABA) (Bartels & Sunkar 2005). ...
Desiccation-tolerance (DT), the ability to lose virtually all free intracellular water and then recover normal function upon rehydration, is one of the most remarkable features of bryophytes. The physiology of bryophytes differs in major respects from that of vascular plants by virtue of their smaller size; unlike vascular plants, the leafy shoots of bryophytes equilibrate rapidly with the water potential in their surroundings and tend to be either fully hydrated or desiccated and metabolically inactive. The time required to recover from desiccation increases and degree of recovery decreases with length of desiccation; both also depend upon temperature and intensity of desiccation. Tolerance in at least some species shows phenotypic plasticity. Recovery of respiration, photosynthesis and protein synthesis takes place within minutes or an hour or two; recovery of the cell cycle, food transport and the cytoskeleton may take 24 hours or more. Positive carbon balance is essential to survival of repeated cycles of drying and wetting; significant growth requires continuously wet periods of a few days or more. Male and female gametophytes, and gametophyte and sporophyte, may differ in tolerance. Desiccation-tolerance is essential to dispersal and establishment of spores and vegetative propagules. The mechanisms of DT in bryophytes, including expression of LEA proteins, high content of non-reducing sugars and effective antioxidant and photo-protection, are at least partly constitutive, allowing survival of rapid drying, but changes in gene expression resulting from mRNA sequestration and alterations in translational controls elicited upon rehydration are also important to repair processes following re-wetting. Phylogenetic and ecological considerations suggest that DT is a primitive character of land plants, lost in the course of evolution of the homoiohydric vascular-plant shoot system, but retained in spores, pollen and seeds, and re-evolved in the vegetative tissues of vascular "resurrection plants." Bryophytes have retained the poikilohydry and DT that are probably the optimal pattern of adaptation at their scale, but modern bryophytes are specialized and diverse, and are removed by the same span of evolutionary time as the flowering plants from their primitive origins.
... Improved salt stress Igarashi et al., 1997 ( Plant-aldehyde dehydrogenase genes and abiotic stress tolerance lar basis of desiccation tolerance (Phillips et al., 2002). Kirch et al. (2001) reported the molecular characterization of a novel class of plant-ALDHs: Cp-ALDH from Craterostigma plantagineum and Ath-ALDH3 from Arabidopsis thaliana showing 70% similarity to each other. ...
The deleterious effect of osmotic stress is often caused by the ac-cumulation of reactive molecules e.g. aldehydes. These molecules can cause lipid peroxidation and modifications of proteins and nucleic acids. Aldehydes can be converted to non-toxic carboxylic acids by different aldehyde de-hydrogenases (ALDH). ALDHs occur in all organisms implicating their im-portance in general biological functions. Aldehydes do not only represent toxic molecules but they are also intermediate products in the synthesis of osmolytes which have been shown to be protective molecules in osmotic stress. For this reason a careful balance of aldehydes is required. Evidence emerges that ALDH enzymes are involved in maintaining this balance, and the investigation of the physiological role of plant-ALDHs begins to attract attention. This review tries to summarize the current knowledge of stress-regulated ALDHs in plants. It describes how ALDHs can be used to obtain more stress tolerant plants by overexpressing ALDH genes. ALDH genes have been used in two ways: 1. to obtain increased accumulation of osmolytes e.g. glycine betaine, 2. to detoxify aldehydes.
... Among the upregulated proteins identified, at least three are associated with antioxidant metabolism, two with photosynthesis and two with energy metabolism (Table I). The relatively small number of proteins that were upregulated specifically during the rehydration phase supports the hypothesis that most changes in the gene expression occur during the dehydration phase in desiccation tolerant higher plants (Phillips et al., 2002). Some of the proteins identified by Ingle et al. (2007) and Jiang et al. (2007) are discussed briefly below. ...
In this chapter, we review the current understanding of desiccation tolerance in the vegetative tissues of resurrection plants. We present an overview of the stresses associated with desiccation and the physiological and biochemical protection reported to result in amelioration of these stresses and discuss the contribution of the genomics era in furthering our understanding of these protection systems in the attainment of desiccation tolerance. We discuss the advances made in proteomics and give a brief overview of recent contributions in the field of metabolomics that have contributed to the understanding of desiccation tolerance.
The sections in this article are
Introduction
Classifications of Dormancy
Definitions of Dormancy
Primary Dormancy
Secondary Dormancy
Signaling in Dormancy
Challenges for the Future
The Series of experiments were carried out to determine the sensitivity of five (Sodari, Ghibaish, Barberton, ICGV121 and Advance) groundnut genotypes (Arachis hypogaea L.) to desiccation under 7 saturated salt solutions with specific relative humidity at 35ºC and freezing in liquid nitrogen temperature (-196ºC) using desorption drying method. The objectives of the study are to quantify seed desiccation and freezing sensitivity and their relations to seed viability. The equilibrium seed water content of desiccated seeds, germination percentages and rates of desiccated and desiccated-frozen seeds, WC50, water activity, water potential, HMFL and their correlations with other parameters were determined. Equilibrium mean water content in gH2Og-1dw was determined gravimetrically when seeds were oven-dried under 105ºC for 24hrs. Seed desiccation sensitivity, (designated as WC50) was obtained using the Quantal Quadric response model. Freezing sensitivity was determined using high moisture freezing limit (HMFL). The significant increases in seed viability (germination percentage) with decreases in equilibrium water content observed in this study. All seeds with stand low level of equilibrium water content (below 0.1 gH2Og-1dw) implying that there were not sensitive to desiccation and freezing as determined by sensitivity indicators (WC50, wa50, Ψ50 and HMFL). In contrast, Barberton, Ghibaish and the Advance line showed less sensitivity to liquid nitrogen (HMFL value of 0.1 gH2Og-1dw) compared to Sodari and ICGV121 (HMFL values of 0.06 and 0.05 gH2Og-1dw, respectively). Correlation analyses indicated that equilibrium seed water content was positively correlated with seed germination after desiccation and freezing. WC50 was positively correlated with HMFL indicating that the sensitivity of seeds to freezing depends upon its level of desiccation.
Досліджували особливості метаболізму вуглеводів і катіонообмінну здатність клітинних стінок мохів Вarbula unquiculata Hedw., Funaria hygrometrica Hedw., Didymodon tophaceus (Brid.) Lisa, Bryum caespiticium Hedw. i Brachythecium campestre (Müll. Hal.) Schimp. залежно від рівня засолення субстрату на території хвостосховища відходів видобутку калійних солей Стебницького гірничо-хімічного підприємства «Полімінерал». Визначено хімічний іонний склад водних витяжок із проб субстрату, відібраних із території хвостосховища. За аніонним складом встановлено сульфатний тип засолення cубстрату. Показано, що пристосування бріофітів до засолення субстрату забезпечується зміною спрямованості метаболічних процесів, яка проявляється у збільшенні загального вмісту вуглеводів і перерозподілі вуглеводного обміну в напрямі гідролізу полісахаридів та накопичення розчинних вуглеводів. Зміна активності α-амілази у пагонах мохів є чутливим маркером сольового стресу. Підвищення амілазної активності призводить до збільшення пулу розчинних вуглеводів і посилення резистентності бріофітів до сольового стресу. Катіонообмінна ємність клітинних стінок мохів має важливе значення у формуванні солестійкості бріофітів. Це величина непостійна, залежить від видових особливостей мохів та інтенсивності сольового стресу.
Complex analysis of the morphological and physiological adaptive reactions of moss Bryum argenteum growing under the conditions of crude oil contamination has been carried out. It has been shown that plant resistance depended on the state of pigmental system. A increase in anthocians and carotenoids content under the conditions of oil contamination has been revealed. The mechanisms of physiological adaptation of B argenteum plants to water deficit induced by the crude oil contamination have been analysed. High regeneration ability of B. argenteum bulbils under the conditions of water deficit was experimentally shown. A decrease in water potential and increase of osmotic protectors (sugars and proline) content in the plants cells of B. argenteum growing on crude oil polluted territory, have been demonstrated. An increase in general antioxidant activity of low-molecular antioxidants in the B. argenteum plants under the conditions of crude oil contamination has been established. The role of nonspecific physiological adaptation mechanisms in forming moss B. argenteum resistance to the influence of unfavorable factor is discussed.
Drought tolerant species from 26 Korean native plants were selected using different stoma, leaf mesophyll, and biochemocal indicators. The largest number of stoma was founded in Artemisia keiskeana and the numbers of stoma in Kummerowia striata, Morus alba, Elsholtzia ciliata were larger than the others. The circumference and area of leaf stoma were inversely related to the number of stoma. Rumex crispus, Panicurr bisulcatum, and Arundinella hirta were a few in stoma number, but they were largest in circumference and stoma area. In observing leaf mesophyll tissues, palisade parenchyma in Ulmus parvifolia was well developed even in drought tolerant species compare to Aster ageratoides, a drought sensitive species. Cuticle layer in Ulmus parvifolia was thicker than that of Aster ageratoides. After stopping of irrigation, proline content of Lespedeza cuneata was somewhat increased but, Saussurea pulchella was dramatically increased. Contents of reducing sugar was highest in Catalpa bignonioides. Proline and reducing sugar content were both increased when drought stressed out. Stoma and leaf mesophyll tissue shapes, biochemical indics as proline and reducing sugar content are proven as critical factors to selection for drought tolerance plants. These results could be used to restoration of damaged land.
The molecular, cellular and biochemical responses of plants to water-deficit stress are the central, and long-term, interest of our respective research programs. We utilize the desiccation-tolerant moss Tortula ruralis (Hedw.) Gaerten., Meyer Scherb. as an experimental model for studying post-transcriptional gene control, molecular & biochemical responses to abiotic stress, cellular repair mechanisms in plants and as a source of novel tolerance-associated genes. In this chapter we will introduce the molecular and biochemical mechanisms of desiccation-tolerance in mosses, describe the molecular and genomics tools that have been developed for T. ruralis (such as EST databases, cDNA libraries, and microarrays), and discuss the expression analysis of several cDNA clones (i.e. the rehydrins Tr288 & Tr213, the aldehyde dehydrogenases Aldh7B6 & Aldh21A1, and the early light-inducible proteins Elipa & Elipb) that are associated with desiccation-stress.
Disparate sex ratios are a widespread pattern in dioecious bryophytes, with female-biased ratios especially prevalent in arid environments. The absence of male plants in environments experiencing high desiccation pressure prompted the hypothesis that male plants may be less desiccation tolerant than female plants in the desert moss Syntrichia caninervis. This hypothesis was investigated by exposing detached leaves to consecutive wet/rapid-dry treatments and monitoring viability, protonemal emergence time, shoot production, growth rate of secondary protonemata, and microbial infection frequency over a 56-d period. The desiccation treatment consisted of exposure of mature 1-yr-old leaves to zero, two, four, and six wet/rapid-dry cycles. Hydrated leaves were then allowed to regenerate. Desiccation stress level was significantly correlated to reduced protonemal emergence, reduced growth rates, and reduced shoot production. Female detached leaves produced protonemata more quickly, and these protonemata grew twice as rapidly and eventually produced more shoots than male detached leaves. Male leaves were also more subject to mortality and microbial infection, although these trends were not statistically significant. No sex x desiccation stress interactions occurred in the stress responses measured. The disparity in growth rates between female and male leaf regeneration, under both stressed and nonstressed conditions, may play a significant role in male rarity. We conclude (i) that the leaf regeneration assay works well as a response variable for desiccation tolerance (DT) studies and (ii) that sex-based DT, at least with respect to responses to rapid drying cycles in the lab, while not indicated in Syntrichia, may yet operate under field conditions.
Introduction: Some Definitions and Preliminary Explanations Concluding Statements
The resurrection plant Craterostigma plantagineum can tolerate up to 96% loss of its relative water content and recover within hours after rehydration. In callus tissue desiccation tolerance is induced by pre-incubation with Abscisic acid (ABA). In callus and plant ABA treatment and dehydration induce a set of dehydration-responsive genes. T-DNA activation tagging led to the identification of CDT-1, a dehydration- and ABA-responsive gene, which renders calli tolerant without ABA pre-incubation. Molecular analysis indicated that CDT-1 is a retroelement, present in multiple copy in the genome, able to direct the synthesis of small RNAs responsible for desiccation tolerance. Transposition of CDT-1 retroelements have progressively increased the capacity of the species to synthesize small RNAs and thus recover after desiccation. This may be a case of evolution towards the acquisition of a new trait, stimulated by the environment acting directly on intra-genomic DNA replication.
The aim of this study was to evaluate the carbon compounds and chlorophyll contents in Sorghum plants (cv. BR-700) submitted to water deficit at vegetative, reproductive and maturation stages. The experimental design used was entirely randomized in factorial scheme, with 2 conditions (control and stress) combined with 3 stages (vegetative, reproductive and maturation; 30, 60 and 90 days after the beginning of experiment, respectively). The total soluble carbohydrates presented significant increases of 45.2 and 61.2% during vegetative and reproductive stages, respectively, and in maturation period a decrease of 62.2%. The sucrose level in stress plants presented the increases of 32.9 and 24.3%, respectively, in the vegetative and reproductive stages; and in maturation stage a reduction of 22.2 mg g DM -1 to 11.0 mg. g DM -1 under control and stress treatments, respectively. The water deficit affected significantly the chlorophyll a, b, total chlorophyll and carotenoid levels in all stages, as well as the decreases in total chlorophyll were 38, 28 and 60% in the vegetative, reproductive and maturation stages, respectively. The study revealed that the total soluble carbohydrates and sucrose presented similar behavior with increases in vegetative and reproductive stages, and in maturation significant decreases. Therefore, the increases were provoked by the mechanism of osmotic adjustment and the decreases occurred due to the transport of reserve compounds. The leaf relative water content and starch were reduced in all the evaluated periods. The chlorophyll a, b, total chlorophyll and carotenoids significantly decreased in all stages after the water restriction.
Fucose-containing sulfated polysaccharides can be extracted from the brown seaweed, Sargassum sp. It has been reported that fucose-rich sulfated polysaccharides from brown seaweeds exert different beneficial biological
activities including anti-inflammatory, anticoagulant, and anti-viral effects. Classical extraction of fucose-containing sulfated
polysaccharides from brown seaweed species typically involves extended, multiple-step, hot acid, or CaCl2 treatments, each step lasting several hours. In this work, we systematically examined the influence of acid concentration
(HCl), time, and temperature on the yield of fucose-containing sulfated polysaccharides (FCSPs) in statistically designed
two-step and single-step multifactorial extraction experiments. All extraction factors had significant effects on the fucose-containing
sulfated polysaccharides yield, with the temperature and time exerting positive effects, and the acid concentration having
a negative effect. The model defined an optimized single-step FCSPs extraction procedure for Sargassum sp. (a brown seaweed). A maximal fucose-containing sulfated polysaccharides yield of ∼7% of the Sargassum sp. dry matter was achieved by the optimal extraction procedure of: 0.03M HCl, 90°C, 4h. HPAEC-PAD analysis confirmed that
fucose, galactose, and glucuronic acid were the major constituents of the polysaccharides obtained by the optimized method.
Lower polysaccharide yield, but relatively higher fucose content was obtained with shorter extraction time. The data also
revealed that classical multi-step extraction with acid ≥0.2M HCl at elevated temperature and extended time had a detrimental
effect on the FCSPs yield as this treatment apparently disrupted the structural integrity of the polymer and evidently caused
degradation of the carbohydrate chains built up of fucose residues.
KeywordsFucoidan–
Sargassum
–Brown seaweed–Fucose–Bioactive compound–Extraction method
Desiccation tolerance (DT) is defined as the equilibration of protoplasmic water potential with that of the surrounding air
(generally dry) without loss of viability upon rehydration. Vegetative DT is widespread among mosses and lichens, but is relatively
rare in vascular plants (0.15%). Recent studies of selected resurrection species indicate that while resurrection plants might
have evolved unique adaptive proteins, enzymes, and antioxidants, the molecular genetic basis of DT lies in the orchestration
of transcriptional and posttranscriptional regulatory programs that operate during drying and rehydration. DT requires signaling
pathways and regulatory mechanisms, aspects of which resemble developmental programs present in orthodox seeds, which result
in the accumulation of oligosaccharides, stress adaptive proteins, antioxidants, reactive oxygen scavenging enzymes, as well
as alterations in the composition and structure of membrane lipids. Functional genomics studies using transcriptome, proteome,
and metabolome analyses are just beginning to unravel the system complexity required to orchestrate the metabolic symphony
that is DT. The status of current gene discovery efforts is summarized along with major transcriptome technologies available
currently to conduct desiccation sensitive versus tolerant species comparisons. These strategies, integrated with large-scale
proteomic and metabolomic investigations currently in progress, promise to revolutionize our understanding of the mechanistic
basis of desiccation tolerance in resurrection plants.
Water stress is a common environmental constraint in terrestrial ecosystems. Among the various strategies to cope with temporal lack of water, poikilohydry is an important adaptive trait under specific habitat conditions. Desiccation tolerant vascular plants are particularly common among ferns, fern allies, and angiosperms that colonize forest canopies and mainly tropical rock outcrops (e.g., granitic/gneissic inselbergs, ferricretes) where environmental conditions (e.g., high temperatures, lack of water, and soil) are harsh.
Xerophyta humilis (Bak.) Dur and Schinz is an indigenous Southern African resurrection plant which is able to protect itself from the stresses associated with extreme dehydration. For the purpose of analysing global patterns of gene expres-sion in response to desiccation and recovery on rehydration, we have generated a normalized 10 900 library, representing genes from root and leaf tissue that are expressed during the dehydration-rehydration cycle. For the small-scale microarray analysis described here, 424 cDNAs were sequenced, anno-tated, arrayed and hybridized with hydrated and dehydrated, leaf-specific RNA. Reverse Northern blots were used as an alternative method to compare the expression results. A total of 55 dehydration-inducible cDNAs were identified combining the results of both methods. Northern blot analysis of 14 of the 55 the dehydration-upregulated cDNAs verified the expression status of all 14 genes. Dehydration-upregulated cDNAs included those homologous to known dehydration stress-responsive genes encoding metallothioneins, galactinol synthases, an aldose reductase and a glyoxalase. A large number of genes encoding late embryonic abundant proteins (LEAs), dehydrins and desiccation-related proteins were also identified, suggesting that proteins that provide mechan-ical and antioxidant protection against water loss dominate the mRNA population in desiccated X. humilis leaf tissue. Dehydration-upregulated genes identified in this study, and not previously implicated in the dehydration response, include cDNAs encoding a putative chloroplast RNA-binding protein and a protein containing SNF2/helicase domains. Com-parisons with microarray data, which profile the dehydration response in desiccation-sensitive plants, reveal differences in expression patterns between X. humilis and Arabidopsis and rice that could provide clues as to the mechanisms underlying desiccation-tolerant and -sensitive phenotypes. The X. humilis library promises to be a useful resource for transcript profiling the dehydration and rehydration response in a desiccation-tolerant plant.
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