No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Comparison of the freezing behavior of two liverwort species – Conocephalum salebrosum and Marchantia polymorpha subsp. ruderalis
... This mechanism was visualized by ESEM on vesicular plants, such as Conocephalum salebrosum and Marchanthia polymorpha L. subsp. ruderalis in 2021 [85]. Ice formation was observed in the range of temperatures between −5 and −10 • C within the air chambers of both species, with ice crystals growing out of the air chamber pores. ...
Scanning electron microscopy (SEM) is a powerful imaging technique able to obtain astonishing images of the micro- and the nano-world. Unfortunately, the technique has been limited to vacuum conditions for many years. In the last decades, the ability to introduce water vapor into the SEM chamber and still collect the electrons by the detector, combined with the temperature control of the sample, has enabled the study of ice at nanoscale. Astounding images of hexagonal ice crystals suddenly became real. Since these first images were produced, several studies have been focusing their interest on using SEM to study ice nucleation, morphology, thaw, etc. In this paper, we want to review the different investigations devoted to this goal that have been conducted in recent years in the literature and the kind of information, beyond images, that was obtained. We focus our attention on studies trying to clarify the mechanisms of ice nucleation and those devoted to the study of ice dynamics. We also discuss these findings to elucidate the present and future of SEM applied to this field.
Die Literaturzusammenstellung erhebt keinen Anspruch auf Vollständigkeit. Sie berücksichtigt überwiegend Publikationen aus dem Jahr 2021, sowie Nachträge aus dem Jahr 2020 und beinhaltet hauptsächlich Fachbücher und Fachartikel zu Studien und Fundberichten über Moose in Mitteleuropa. Zusätzlich sind außereuropäische Arbeiten aufgelistet, die aufgrund der behandelten Arten oder Methoden von Interesse sind. Für aktuelle Veröffentlichungen mit Fokus auf Taxonomie und Systematik sei auf den Beitrag „Taxonomische und nomenklatorische Neuerungen – Moose, von Markus K. Meier in diesem Herzogiella-Heft verwiesen. Für Hinweise auf entsprechende Publikationen für kommende Folge dieser Serie sind wir dankbar.
One of the classical research plants in plant biology, Marchantia polymorpha, is drawing attention as a new model system. Its ease of genetic transformation and a genome sequencing project have attracted
attention to the species. Here I present a thorough assessment of the taxonomic status, anatomy, and developmental morphology
of each organ and tissue of the gametophyte and sporophyte on the basis of a thorough review of the literature and my own
observations. M. polymorpha has been a subject of intensive study for nearly 200 years, and the information summarized here offers an invaluable resource
for future studies on this model plant.
Controlled ice nucleation is an important mechanism in cold hardy plant tissues for avoiding excessive supercooling of the protoplasm, for inducing extracellular freezing and/or for accommodating ice crystals in specific tissues. To understand its nature, it is necessary to characterize the ice nucleation activity (INA), defined as the ability of a tissue to induce heterogeneous ice nucleation. Few studies have addressed precise localization of INA in wintering plant tissues in respect of its function. For this purpose, we recently revised a test tube INA assay and examined INA in various tissues of over 600 species. Extremely high levels of INA (-1∼-4 °C) in two wintering blueberry cultivars of contrasting freezing tolerance were found. Their INA was much greater than in other cold hardy species and was found evenly distributed along the stem of current year's growth. From quantitative analyses, concentrations of active ice nuclei in the stem were estimated. Stem INA was localized mainly in the bark whilst the xylem and pith had much lower INA. Bark INA was located mostly in the cell wall fraction (cell walls and intercellular structural components). Intracellular fractions had much less INA. Some cultivar differences were identified. The results corresponded closely with the intrinsic freezing behavior (extracellular freezing) of the bark, icicle accumulation in the bark and initial ice nucleation in the stem under dry surface conditions. Stem INA was resistant to various antimicrobial treatments. These properties and specific localization imply that high INA in blueberry stems is of intrinsic origin and contributes to the spontaneous initiation of freezing in extracellular spaces of the bark by acting as a subfreezing temperature sensor.
Ice nucleation activity (INA) of plant intrinsic origins is considered to play important roles in plant cold hardiness mechanisms. Yet, only a few studies have addressed the spatial and temporal localization of plant INA, how it is regulated and what its functional roles are. In our previous study (Kishimoto et al., 2014), we revised a test tube method and developed a highly reproducible assay for measuring INA of plant specimens and demonstrated that high INA occurred in the cell wall fraction of wintering bark tissues of blueberry stems and corresponded well to the freezing behavior (extracellular freezing) of the stem bark. Here, we followed precisely seasonal changes in the stem INA of two blueberry cultivars and alterations in the stem INA caused by artificial incubation at various low temperatures. INA of newly developed shoots was low but increased rapidly by July when the stem became seemingly matured, then gradually increased with the maximum in October or early November just before the first autumnal frost. Following the subsequent recurrent frosts, the stem INA gradually decreased. This tendency was consistent between the two cultivars differing in the level of cold hardiness. INA in the stems of September until February was increased by incubation at 0-7 °C whilst decreased by freezing to lower temperatures. The in vitro results corroborate the seasonal changes in the stem INA in the field but the mechanisms remain to be investigated. The highest level of INA (expressed as the median ice nucleation temperature) observed with current year stems (7.5 mm-long) of Woodard in October of 2010-2013 was -0.9 ∼ -1.0 °C when determined with 2 mL assay system (-1.1 ∼ -1.3 °C with 0.5 mL system). This may likely be one of the highest INA of biological origins ever reported.
In the course of a year, perennial plants in temperate climates are exposed to several types of freezing stress including low temperature extremes, ice encasement, and unseasonable episodes of frost. Many plants can adapt to survive freezing through a process of cold acclimation. This is a complex process with many contributing factors.1 Cold acclimation is also a dynamic process. Not only does it exhibit a distinct seasonality but the mechanisms that confer cold hardiness in midwinter may differ from those in late winter or early spring. This is further complicated by the discovery that in many perennial woody plants, and some herbaceous plants, tissues within the same plant can respond very differently to exposure to freezing temperatures.
Detailed analysis of 270 specimens of Conocephalum conicum (L.) Dumort., mainly from the POZW Herbarium revealed some diagnostic differences between two cryptic species originally detected on the basis of isozyme studies. Several diagnostic characters were found in the structure of the archegoniophore, sporophyte and sterile thallus. The most reliable diagnostic features are size and structure of stomatal apparatus of the archegoniophore ‘heads’, type of junction of the air chamber walls with epidermal cells, and the thallus surface details. On the basis of morphological and anatomical diagnostic characters, two formerly cryptic species are recognized following the rules of formal taxonomy. The lectotype of C. conicum preserved in FI was found to possess characteristics of cryptic species C. conicum- species L. Accordingly, the species previously named as C. conicum–species L must bear the name Conocephalum conicum (L.) Dumort. No published name was related to C. conicum – species S, which is therefore described as a new species: Conocephalum salebrosum Szweykowski, Buczkowska & Odrzykoski. Both species are fully described and their diagnostic characters are illustrated. Distribution maps for both species are given.
The relative effect of a freeze-thaw cycle on photosynthesis, respiration, and ion leakage of potato leaf tissue was examined in two potato species, Solanum acaule Bitt. and Solanum commersonii Dun. Photosynthesis was found to be much more sensitive to freezing stress than was respiration, and demonstrated more than a 60% inhibition before any impairment of respiratory function was observed. Photosynthesis showed a slight to moderate inhibition when only 5 to 10% of the total electrolytes had leaked from the tissue (reversible injury). This was in contrast to respiration which showed no impairment until temperatures at which about 50% ion leakage (irreversible injury) had occurred. The influence of freeze-thaw protocol was further examined in S. acaule and S. commersonii, in order to explore discrepancies in the literature as to the relative sensitivities of photosynthesis and respiration. As bath cooling rates increased from 1 degrees C/hour to about 3 or 6 degrees C/hour, there was a dramatic increase in the level of damage to all measured cellular functions. The initiation of ice formation in deeply supercooled tissue caused even greater damage. As the cooling rates used in stress treatments increased, the differential sensitivity between photosynthesis and respiration nearly disappeared. Examination of agriculturally relevant, climatological data from an 11 year period confirmed that air cooling rates in the freezing range do not exceed 2 degrees C/hour. It was demonstrated, in the studies presented here, that simply increasing the actual cooling rate from 1.0 to 2.9 degrees C/hour, in frozen tissue from paired leaflet halves, meant the difference between cell survival and cell death.
In frost hardy plants, the lethal intracellular formation of ice crystals has to be prevented during frost periods. Besides the ability for supercooling and pre-frost dehydration of tissues, extracellular ice forma- tion is another strategy to control ice development in tissues. During extracellular ice formation, partially large ice bodies accumulate in intercellular spaces, often at preferred sites which can also be expand- able. In this contribution, the physico-chemical processes underlying the water movements towards the sites of extracellular ice formation are studied theoretically, based on observations on the frost hardy horsetail species Equisetum hyemale , with the overall aim to obtain a better understanding of the physical processes involved in extracellular ice formation. In E. hyemale , ice accumulates in the extensive internal canal system. The study focuses on the processes which are triggered in the cellular osmotic-mechanic system by falling, and especially subzero temperatures. It can be shown that when the temperature falls, (1) water flow out of cells is actuated and (2) “stiff-walled”cells lose less water than “soft-walled”cells. Furthermore, (3) cell water loss increases with increasing ( = less negative) turgor loss point. These pro- cesses are not related to any specific activities of the cell but are solely a consequence of the structure of the cellular osmotic system. On this basis, a directed water flow can be initiated triggered by subzero temperatures. The suggested mechanism may be quite common in frost hardy species with extracellular ice formation.
In this study, the ice nucleation activity (INA) and ice nucleation temperature
(INT) as well as extracellular ice formation within the bark were determined
for three woody species with different degrees of frost resistance, Betula nana,
Betula albosinensis and Castanea sativa. Current-year stems and at least 2-year
old stems of B. nana and C. sativa as well as current-year stems of B. albosinensis
were compared, during summer (non-acclimated state) and winter (acclimated
state), to evaluate possible ontogenetic and seasonal differences. Acclimated
plant parts of the selected species revealed nearly similar results, with an INT
from -7.52 to -8.43°C. The current-year stems of B. nana had a somewhat
higher INT than the older stems. Microscopic analysis showed that extracellular
ice formation occurred in the intercellular spaces within the bark of stems
of B. nana, B. albosinensis and C. sativa. Size of the intercellular spaces of the
bark were species-specific, and B. nana showed the largest intercellular space
volume. While freezing behavior and extracellular ice formation thus followed
principally the same pattern in all considered species, B. nana is obviously
capable of dealing with large masses of extracellular ice which accumulate over
extended periods of frost, making B. nana capable of protecting living tissue in
colder regions from freezing damage.
Formation of extracellular ice at specific positions in the plant interior is a common and probably essential component of plant cold hardiness. Studies on extracellular freezing in spore-bearing plants are, however, scarce. In this study, extracellular ice formation in the cold hardy horsetail Equisetum hyemale L. is analyzed. Horsetails show an extensive system of intercellular air spaces which are probably crucial for internal ice storage during winter. Previous studies emphasized the spacious pith cavity as the main place for ice crystal growth. Shoots were studied during summer and in the frozen state in winter, after natural acclimatization, by using digital (incident light) microscopy, Scanning Electron Microscopy and Cryo Scanning Electron Microscopy. It was shown that the vallecular canals also contain a large share of ice bodies under freezing conditions. The vallecular canals, which are directly seated within the cortex and whose interior is directly connected to the cortex via gaps in the canal wall, were often and rapidly filled with ice. The pith cavity also contained ice, depending on the position along the shoot and the internode. The carinal canals contained almost no ice crystals. Furthermore, some ice crystals were detected in the intercellular spaces of the chlorenchyma and the substomatal chamber. The stomatal antechamber, however, was always ice-free, probably due to the presence of water-repellent wax crystals. The results of this study support available evidence for the crucial role of pre-existing extensive lacunae for extracellular ice formation in E. hyemale. Furthermore, the findings indicate that anatomical details of canal structure and position are important for the pattern of extracellular ice accumulation.
In the early 1980's a considerable amount of research focused on the role of extrinsic ice nucleation and its= role in inducing plants to freeze at warm sub-zero temperatures. The working hypothesis was that by controlling extrinsic nucleation events, plants could supercool well below 0 °C and thus avoid freezing (Lindow, 1995). It was felt that such a strategy could provide a significant level of frost protection to frost sensitive plants or plant parts. While the majority of reports dealt with the role of ice-nucleating-active (INA) bacteria (e.g. Pseudomonas syringae), related research focused on the role of other extrinsic nucleating agents and whether or not plants could actually supercool to temperatures several degrees below 0 °C due to the presence of intrinsic nucleating agents which induced the plants to freeze at warm temperatures (Ashworth and Kieft, 1995). The identification of a wide range of both extrinsic and intrinsic ice nucleating agents made the practical application of blocking extrinsic ice nucleation complex. Since that time, research emphasis has switched to identifying genes that impart cold tolerance and the transcriptional activators that regulate cold hardiness genes (Thomashow, 1998; Jaglo, et al., 2001). The hypothesis here is that by the overexpression of these types of genes, a non-acclimated or freeze-sensitive plant could be made freezing tolerant.While great progress has been made in understanding the genetic basis of cold hardiness, manipulation of this trait by molecular biology has also demonstrated itself to be complicated due to the “additional” effects of the overexpression of several cold hardiness genes on the physiology and development of the target plant. Therefore, blocking extrinsic ice nucleation, although complicated, may still be a valuable approach to providing protection to frost sensitive plants.
Air pore geometry of 14 liverwort species was investigated using light, scanning and transmission electron microscopy to assess their ability to prevent water entering into the air pore and the intercellular space of the thallus. The air pores of 12 species [Marchantia polymorpha L., M. paleacea Bertol., M. nitida Lindenberg & Lehmann in Lehmann, Conocephalum conicum (L.) Wiggers, C. supradecompositum (S.O. Lindberg) Stephani, Grimaldia capensis Stephani, Targionia hypophylla L., Lunularia cruciata (L.) Dum., Reboulia hemisphaerica (L.) Raddi, Oxymitra paleacea Bischoff, Exormotheca bullata (Link) K. Müller (Tüb.), Plagiochasma elongatum Lindenberg & Gottsche] are equipped with hydrophobic ledges which constrict the air pore entrance after the fashion of an iris shutter. As a consequence only liquids having a contact angle of zero degree with the ledges are able to penetrate the air pore. The ledge of Marchantia paleacea was found to have a surface composed of methyl and methylene groups as indicated by the critical surface tension of less than 30.4 dyne cm(-1). Evidence is presented that the ledge is covered with a layer of cutin. It is shown that from the standpoint of protection against water entry these air pores must be considered perfect structures. Plagiochasma rupestre (Forster) Stephani and P. peruvianum Nees & Montagne are exceptional as they do not have ledges around their air pores. As a consequence liquids having a finite contact angle are able to enter through the pores into the thallus. Thus, they are imperfect and must be considered primitive.
It is well known that preparation of biological (plant and animal) tissues for Scanning Electron Microscopy (SEM) by chemical fixation and critical point drying results in shrinkage of tissues, often by up to 20-30%, depending on the tissue type and fixation protocol used. We sought to identify a protocol that would preserve tissue size and morphology better than standard chemical fixatives and dehydration regimes. We compared a range of processing techniques by quantifying changes in tissue size and recording details of surface morphology using leaf tissues from three commonly studied species; Arabidopsis thaliana, barley and cotton.
All processing protocols altered tissue dimensions. Methanol fixation and dehydration, followed by a further short (1 h) dehydration step in ethanol and critical point drying (which was based on a previously published method), preserved tissue dimensions most consistently of all protocols tested, although it did cause 8% shrinkage in all three species. This protocol was also best for preservation of surface morphology in all three species. We outline a recommended protocol and advise that the method is best trialled for different tissues, especially thicker or larger samples.
This study shows that simultaneous fixation and dehydration in methanol followed by ethanol results in better preservation of dimensions and morphology of critical point dried plant tissues than other fixation and dehydration procedures. It is a quick and simple method, and requires standard SEM preparation equipment.
Conifers are among the most frost tolerant tree species. Cryo-scanning electron microscopy (cryo-SEM) was used to visualise ice formation in pine needles to better understand how conifer leaves manage extracellular ice. Acclimated and unacclimated needles of Pinus radiata (D.Don) were subjected to freezing treatments (at a rate of 2°Ch-1), tested for electrolyte leakage and sampled for cryo-SEM analysis. Half maximal electrolyte leakage occurred at -4 and -12°C for unacclimated and acclimated needles, respectively. Ice nucleation occurred at similar temperatures (-3°C) in both acclimated and unacclimated pine needles, indicating that frost tolerance did not increase supercooling. During freezing and thawing, the tissues outside and inside the endodermis shrank and swelled independently, with little or no transfer of water between the two regions. During freezing, mesophyll cells shrank, exhibiting cytorrhysis, and extracellular ice accumulated in gas spaces of the mesophyll tissue. Mesophyll cells from acclimated needles recovered their structure after thawing, and unacclimated mesophyll showed significant damage. In the vascular cylinder, ice accumulated in transfusion tracheids which expanded to occupy areas made vacant by shrinkage of transfusion parenchyma, Strasburger cells and the endodermis. This behaviour was reversible in acclimated tissue, and may play an important role in the management of ice during freeze/thaw events.
Freeze-induced damage to leaf tissues was studied at different states of acclimation to low temperatures in snow gum, Eucalyptus pauciflora Sieber ex Sprengel. Intact, attached leaves of plants grown under glasshouse or field conditions were frozen at natural rates (frost-freezing) and thawed under laboratory conditions. Leaves were cryo-fixed unfrozen, during frost-freezing or after thawing for observation in a cryo-scanning electron microscope. Frost-freezing in unacclimated tissues caused irreversible tissue damage consistent with tissue death. Intracellular ice formed in the cambium and phloem, killing the cells and leaving persistent gaps between xylem and phloem. Many other cells were damaged by frost-freeze-induced dehydration and failed to resorb water from thawed extracellular ice, leaving substantial amounts of liquid water in intercellular spaces. In contrast, acclimated leaves showed reversible tissue displacements consistent with leaf survival. In these leaves during freezing, massive extracellular ice formed in specific expansion zones within the midvein. On thawing, water was resorbed by living cells, restoring the original tissue shapes. Possible evolutionary significance of these expansion zones is discussed. Acclimated leaves showed no evidence of intracellular freezing, nor tissue lesions caused by extracellular ice. While the observations accord with current views of freeze-sensitivity and tolerance, cryo-microscopy revealed diverse responses in different tissue types.
Extracellular freezing occurs within the pith cavities of Equisetum hyemale L. aerial shoots when they are exposed to subfreezing temperatures. The weight of plugs of ice within pith cavities correlates linearly with the weight of intemodal tissues (r2 = 0.974, N = 10); ice plugs are 32-38% (33 ? 1.8%) the weight of intact shoots. Upon thawing, internodal water is gradually reabsorbed by excised shoots. Extracellular freezing can be induced by exposing excised shoots to gradually decreasing temperatures (5 C/day) to - 20C, and is associated with a reduction in tissue water potential. Data indicate that internodal tissues behave as osmometers and dehydrate until reaching equilibrium with the chemical potentials of extracellular fluids within intemodal pith cavities. Upon thawing, intemodal water is reabsorbed by excised shoots and tissue water potential increases. Extracellular freezing may operate as a mechanism that reduces intracellular ice formation and tissue damage during extremely cold weather.
How plants adapt to freezing temperatures and acclimate to survive the formation of ice within their tissues has been a subject of study for botanists and plant scientists since the latter part of the 19th century. In recent years, there has been an explosion of information on this topic and molecular biology has provided new and exciting opportunities to better understand the genes involved in cold adaptation, freezing response and environmental stress in general. Despite an exponential increase in our understanding of freezing tolerance, understanding cold hardiness in a manner that allows one to actually improve this trait in economically important crops has proved to be an elusive goal. This is partly because of the growing recognition of the complexity of cold adaptation. The ability of plants to adapt to and survive freezing temperatures has many facets, which are often species specific, and are the result of the response to many environmental cues, rather than just low temperature. This is perhaps underappreciated in the design of many controlled environment experiments resulting in data that reflects the response to the experimental conditions but may not reflect actual mechanisms of cold hardiness in the field. The information and opinions presented in this report are an attempt to illustrate the many facets of cold hardiness, emphasize the importance of context in conducting cold hardiness research, and pose, in our view, a few of the critical questions that still need to be addressed.
Using cryo-SEM with EDX fundamental structural and mechanical properties of the moss Ceratodon purpureus (Hedw.) Brid. were studied in relation to tolerance of freezing temperatures. In contrast to more complex plants, no ice accumulated within the moss during the freezing event. External ice induced desiccation with the response being a function of cell type; water-filled hydroid cells cavitated and were embolized at -4 °C while parenchyma cells of the inner cortex exhibited cytorrhysis, decreasing to ∼ 20% of their original volume at a nadir temperature of -20 °C. Chlorophyll fluorescence showed that these winter acclimated mosses displayed no evidence of damage after thawing from -20 °C while GCMS showed that sugar concentrations were not sufficient to confer this level of freezing tolerance. In addition, differential scanning calorimetry showed internal ice nucleation occurred in hydrated moss at ∼-12 °C while desiccated moss showed no evidence of freezing with lowering of nadir temperature to -20 °C. Therefore the rapid dehydration of the moss provides an elegantly simple solution to the problem of freezing; remove that which freezes.
A replica plating method for rapid quantitation of ice nucleation-active (INA) bacteria was developed. Leaf washings of plant samples from California, Colorado, Florida, Louisiana, and Wisconsin were tested for the presence of INA bacteria. Of the 95 plant species sampled, 74 were found to harbor INA bacteria. Only the conifers were, as a group, unlikely to harbor INA bacteria. All of the INA bacteria isolated resembled either Pseudomonas syringae or Erwinia herbicola. Sufficient numbers of INA bacteria were present on the samples to account for the ice nuclei associated with leaves that are necessary for freezing injury to occur. Numbers of INA bacteria were large enough to suggest that plant surfaces may constitute a significant source of atmospheric ice nuclei.
Extracellular ice formation in frost-tolerant organisms is often initiated at specific sites by ice nucleators. In this study, we examined ice nucleation activity (INA) in the frost-tolerant plant winter rye (Secale cereale). Plants were grown at 20[deg]C, at 5[deg]C with a long day, and at 5[deg]C with a short day (5[deg]C-SD). The threshold temperature for INA was -5 to -12[deg]C in winter rye leaves from all three growth treatments. Epiphytic ice nucleation-active bacteria could not account for INA observed in the leaves. Therefore, the INA must have been produced endogenously. Intrinsic rye ice nucleators were quantified and characterized using single mesophyll cell suspensions obtained by pectolytic degradation of the leaves. The most active ice nucleators in mesophyll cell suspensions exhibited a threshold ice nucleation temperature of -7[deg]C and occurred infrequently at the rate of one nucleator per 105 cells. Rye cells were treated with chemicals and enzymes to characterize the ice nucleators, which proved to be complexes of proteins, carbohydrates, and phospholipids, in which both disulfide bonds and free sulfhydryl groups were important for activity. Carbohydrates and phospholipids were important components of ice nucleators derived from 20[deg]C leaves, whereas the protein component was more important in 5[deg]C-SD leaves. This difference in composition or structure of the ice nucleators, combined with a tendency for more frequent INA, suggests that more ice nucleators are produced in 5[deg]C-SD leaves. These additional ice nucleators may be a component of the mechanism for freezing tolerance observed in winter rye.
Some frost-tolerant herbaceous plants droop and wilt during frost events and recover turgor and posture on thawing. It has long been known that when plant tissues freeze, extracellular ice forms. Distributions of ice and water in frost-frozen and recovered petioles of Trifolium repens and Escholschzia californica were visualized.
Petioles of intact plants were cryo-fixed, planed to smooth transverse faces, and examined in a cryo-SEM.
With frost-freezing, parenchyma tissues shrank to approx. one-third of their natural volume with marked cytorrhysis of the cells, and massive blocks of extracellular icicles grew under the epidermis (poppy) or epidermis and subepidermis (clover), leaving these layers intact but widely separated from the parenchyma except at specially structured anchorages overlying vascular bundles. On thawing, the extracellular ice was reabsorbed by the expanding parenchyma, and surface tissues again contacted the internal tissues at weak junctions (termed faults). These movements of water into and from the fault zones occurred repeatedly at each frost/thaw event, and are interpreted to explain the turgor changes that led to wilting and recovery. Ice accumulations at tri-cellular junctions with intercellular spaces distended these spaces into large cylinders, especially large in clover. Xylem vessels of frozen petioles were nearly all free of gas; in thawed petioles up to 20 % of vessels were gas-filled.
The occurrence of faults and anchorages may be expected to be widespread in frost-tolerant herbaceous plants, as a strategy accommodating extracellular ice deposits which prevent intracellular freezing and consequent membrane disruption, as well as preventing gross structural damage to the organs. The developmental processes that lead to this differentiation of separation of sheets of cells firmly cemented at determined regions at their edges, and their physiological consequences, will repay detailed investigation.
The management of extracellular ice by petioles of frost-resistant herbaceous plants
- M E Mccully
- M J Canny
- C X Huang
McCully, M. E., Canny, M. J. and Huang, C. X. 2004. The management of extracellular ice by petioles of frost-resistant
herbaceous plants. -Ann. Bot. 94: 665-674.
The air cavities of equisetum as water reservoirs
- J H Schaffner
Schaffner, J. H. 1908. The air cavities of equisetum as water reservoirs. -Ohio Nat. IX: 393-394.
Biological ice nucleation and its applications
- G Vali