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![A model for sucrose transport to a wounded cell. Sucrose is unloaded from the sieve elements (SE) of phloem into the unloading cells (ULC) by plasma membrane sucrose transporters [ ]. Sucrose is transported via the plasma membrane from one apoplastic cell (APC) to the other, to the wounded cell (WDC). Cytosolic invertase (CYT INV) cleaves sucrose to glucose (GLU) and fructose (FRU), which are taken up for cellular metabolism and activation of defense responses. Furthermore, sucrose also leaves the sieve element via the symplastic route by sucrose efflux carriers [ ]. Sucrose is cleaved into glucose and fructose by extracellular invertase (EXT INV) and cell wall invertase (CW INV). The resulting monosaccharides are taken up into the wounded cell by monosaccharide transporters [ ] and used for cellular metabolism and activation of defence response.](profile/Graeme-Bradley/publication/228346068/figure/fig1/AS:654752387964952@1533116542696/A-model-for-sucrose-transport-to-a-wounded-cell-Sucrose-is-unloaded-from-the-sieve.png)
A model for sucrose transport to a wounded cell. Sucrose is unloaded from the sieve elements (SE) of phloem into the unloading cells (ULC) by plasma membrane sucrose transporters [ ]. Sucrose is transported via the plasma membrane from one apoplastic cell (APC) to the other, to the wounded cell (WDC). Cytosolic invertase (CYT INV) cleaves sucrose to glucose (GLU) and fructose (FRU), which are taken up for cellular metabolism and activation of defense responses. Furthermore, sucrose also leaves the sieve element via the symplastic route by sucrose efflux carriers [ ]. Sucrose is cleaved into glucose and fructose by extracellular invertase (EXT INV) and cell wall invertase (CW INV). The resulting monosaccharides are taken up into the wounded cell by monosaccharide transporters [ ] and used for cellular metabolism and activation of defence response.
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Plant cells are commonly exposed to a variety of injuries such as mechanical and herbivore wounding. Wounding is a continual threat to the survival of all organisms and an open wound caused by mechanical or herbivore wounding is a potential infection site for pathogens, thus expression of defense genes at the wound site is a barrier against opportu...
Contexts in source publication
Context 1
... in plants have demonstrated that different stress related stimuli result in the same regulatory pattern of proteins and plant hormones involved in cellular metabolism and defense reactions. Defense response is tightly linked to the up-regulation of sucrose sink meta- bolism to satisfy the energy requirements and the activation of the cascade of defense reactions (Figure 1), thus sucrose and stress related signal transduction path- ways are integrated to regulate defense reactions as well as source-sink relations (Koch, 1996;Rolland et al., 2006;Smeekens, 1998). ...
Context 2
... supply of carbohydrates to sink tissue via an apoplastic pathway involves the release of the trans- ported sucrose into the apoplast by a sucrose transporter, cleavage of dissacharides by invertase and uptake of the hexose to produce the needed energy and carbon. The 3 types of invertase i.e. extracellular, cell wall or cytosolic invertases (Figure 1) are involved in this process (Sturm, 1999). In many plant species however, sucrose leaves the symplast at some point possibly via sucrose efflux carriers and gets actively accumulated into the sieve element companion cell complex by proton coupled sucrose transporters expressed in the companion cells and sieve elements. ...
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Plants defend themselves against herbivores by activating a plethora of genetic and biochemical mechanisms aimed at reducing plant damage and insect survival. The short-term plant response to insect attack is well understood, but less is known about the maintenance of this response over time. We performed transcriptomic and metabolomics analyses in...
Citations
... Sucrose is a major photosynthetic product representing >95% transported carbohydrate in plants phloem, it could reach a concentration of up to 1 M in the conducting vascular cells and 2-7 mM in extracellular space (8). In addition, sucrose would be unloaded from the sieve elements of phloem leading to its accumulation to reach even higher concentration while tissue wounding (9,10). It has also been reported that sucrose plays an important role in wound signaling (11) and endogenous signaling to induce defense responses against pathogens in rice (12). ...
Agrobacterium tumefaciens infects various plants and causes crown gall diseases involving temporal expression of virulence factors. SghA is a newly-identified virulence factor enzymatically releasing salicylic acid from its glucoside conjugate and controlling the plant tumor development. Here we report the structural basis of SghR, a LacI-type transcription factor and highly conserved in Rhizobiaceae family, regulating the expression of SghA and involved in tumorigenesis. We identified and characterized the binding site of SghR on the promoter region of sghA , and then determined the crystal structures of apo-SghR, SghR complexed with its operator DNA and ligand sucrose, respectively. These results provide detailed insights into how SghR recognizes its cognate DNA and shed a mechanistic light on how sucrose attenuates the affinity of SghR with DNA to modulate the expression of SghA. Given the important role of SghR in mediating the signaling crosstalk during Agrobacterium infection, our results pave the way for structure-based inducer analogue design, which has potential applications for agricultural industry.
... When the injury occurs, BnSUT2 pro mainly exhibits wound-induced function. SUT proteins not only play an important role in the distribution of assimilation products but also involve cellular metabolism and defense responses (Ibraheem et al., 2008). In this study, GUS expression was strongly induced by mechanical wounding in Arabidopsis carrying BnSUT2 pro , indicating that the strongly induced expression of BnSUT2 is involved in plant response to external damage resistance. ...
... In this study, GUS expression was strongly induced by mechanical wounding in Arabidopsis carrying BnSUT2 pro , indicating that the strongly induced expression of BnSUT2 is involved in plant response to external damage resistance. Similar results have also been reported in previous studies (Truernit et al., 1996;Sakr et al., 1997;Fotopoulos et al., 2003;Meyer et al., 2004), suggest that up-regulated expression of SUTs in injured or infected tissues can increase the content of carbohydrate and provide energy assurance for increased metabolic activity in these tissues (Meyer et al., 2004;Ibraheem et al., 2008). ...
... During this period, leaf photoassimilates are formed and transported mainly in the form of sucrose (Lalonde et al. 2004; Lbraheem et al. 2008; Lemoine 2000; Reynolds et al. 2012; Xiong et al. 1994), therefore maintaining a high leaf photosynthetic capacity and adequate supply of sugar is advantageous for improving yield. The synthesis and accumulation of starch is closely related to the crop yield as starch accounts for approximately 70 % of the total dry weight of grains (Awika 2011; Jiang et al. 2002a, b, c). ...
The photosynthetic oxygen evolution rate, Hill reaction activity of seedlings and photosynthetic parameter, Pn-Ci curve and some source-sink metabolism-related enzyme activities, and substance content of flag leaves were measured by using two wheat near isogenic lines with significant differences in the photosynthetic rate of the 154 (high photosynthetic rate) and 212 (low photosynthetic rate) lines as materials. The results showed that the maximal carboxylation efficiency (Vcmax) and Hill reaction activity were higher in line 154 than that of line 212. The Pn in flag leaves of line 154 was significantly higher than that of line 212 during the anthesis to grain-filling stage. Higher leaf sucrose phosphate synthase activity, grain sucrose synthase activity, and grain ADPG pyrophosphorylase activity ensured that the photosynthate of line 154 could be transported to grains and translated into starch in a timely and effective manner, which also contributed to the maintenance of its high photosynthetic rate. Eventually, all of these factors of line 154 resulted in its higher grain yield compared with the low photosynthetic rate of line 212.
... As it was found in earlier study sucrose absorption was inhibited with actinomycin D and cycloheximide (Luštinec et al. 1984). All these results suggested that up to 85 % of sucrose absorption was dependent on protein synthesis supported by an internal supply of low-molecular weight nitrogen compounds, and may involve the synthesis of proteinaceous membranebound carriers, induced by wounding and external sucrose (Ibraheem et al. 2008). Sucrose could act by different mechanisms: as a substrate in carbon and energy metabolism, as a hormone-like factor, and as a primary messenger in signal transduction. ...
We describe complex multiple concentration dependencies for the response of isolated pith tissues to plant biologically active substances. Kale and tobacco stem pith explants were cultured on agar media containing combinations of sucrose, cytokinin [kinetin or benzyladenine (BA)] and auxin [indole-3-acetic acid (IAA) or naphthaleneacetic acid (NAA)]. Absorption of these components by explants and their effects on explant mass, contents of soluble proteins, starch and sugars, and activity of ADP-glucose pyrophosphorylase (AGPase) were studied in relation to their concentration. Up to ten pronounced statistically significant maxima (peaks or waves) were repeatedly detected in the dose–response curves over a concentration range of several logarithmic orders. Slight maxima were observed in the corresponding absorption curves. Pronounced maxima of sucrose absorption were induced by IAA and BA, and those of NAA absorption were induced by sucrose. Both types of multiple maxima (in dose–response and absorption curves) may be due to changes in concentration of intracellular solutes (sugars, auxins and cytokinins), thereby affecting metabolic processes that act as sinks for external solutes and elicit feedback appearance of maxima in absorption curves. Good correspondence between external concentrations at which maxima of different compared curves occur in addition to statistical significance of individual maxima and repeatability of experimental results supports the conclusion that the multiple maxima exhibited are genuine. We consider it possibile that the multiple maxima are associated with endopolyploidy or mixoploidy and/or epigenomic diversity of pith cells that show different sensitivities to biologically active solutes.
... Loss of cell integrity means that solute losses must occur and, based on the evidence presented here, solutes (including sugars) will be lost to the apoplast despite rapid wound callose deposition, which often occurs within minutes of wounding (Radford & White 2001;Nakashima et al. 2003;Saheed et al. 2007a,b;de Wet & Botha 2007). Apart from the loss of sugar resulting from aphid feeding, it is known that wounding and pathogen infection elevate sucrose transporter expression (Sakr et al. 1993(Sakr et al. , 1997Truernit et al. 1996;Fotopoulos et al. 2003;Meyer et al. 2004;Rolland et al. 2006;Kempema et al. 2007;Ibraheem et al. 2008). The expression and up-regulation of solute transporters is necessary in order to facilitate recovery and re-absorption. ...
The role of the sucrose transporter OsSUT1 in assimilate retrieval via the xylem, as a result of damage to and leakage from punctured phloem was examined after rusty plum aphid (Hysteroneura setariae, Thomas) infestation on leaves from 3-week-old rice (Oryza sativa L. cv Nipponbare) plants. Leaves were examined over a 1- to 10-day infestation time course, using a combination of gene expression and β-glucuronidase (GUS) reporter gene analyses. qPCR and Western blot analyses revealed differential expression of OsSUT1 during aphid infestation. Wide-field fluorescence microscopy was used to confirm the expression of OsSUT1-promoter::GUS reporter gene in vascular parenchyma associated with xylem elements, as well as in companion cells associated with phloem sieve tubes of large, intermediate and small vascular bundles within the leaf blade, in regions where the aphids had settled and were feeding. Of great interest was up-regulation of OsSUT1 expression associated with the xylem parenchyma cells, abutting the metaxylem vessels, which confirmed that OsSUT1 was not only involved in loading of sugars into the phloem under normal physiological conditions, but was apparently involved in the retrieval of sucrose leaked into the xylem conduits, which occurred as a direct result of aphid feeding, probing and puncturing of vascular bundles. The up-regulation of OsSUT1 in xylem vascular parenchyma thus provides evidence in support of the location within the xylem parenchyma cells of an efficient mechanism to ensure sucrose recovery after loss to the apoplast (xylem) after aphid-related feeding damage and its transfer back to the symplast (phloem) in O. sativa leaves.
... However, fructose arising from fructan degradation is not the form of carbohydrate translocation (Amiard et al. 2003(Amiard et al. , 2004, and it needs to be converted to sucrose for transport. Sucrose transporters are thought to be involved in the export of sucrose to wound sites and growing points under the defoliation process (Ibraheem et al. 2008). Defoliation in Lolium perenne led to the significant increase of the expression of LpSUT1 in leaf sheath, and the increased LpSUT1 transcript levels may contribute to the rapid refoliation (Berthier et al. 2009). ...
Sucrose is a major photosynthetic product in plants’ leaves. Long-distance transport of sucrose requires sucrose transporter (SUT) to perform loading and unloading functions. In this study, a sucrose transporter gene LcSUT1 was cloned from sheep grass (Leymus chinensis (Trin.) Tzvel), a perennial grass of Gramineae: Poaceae. Bioinformatics analysis showed that the gene product LcSUT1 consisting of 12 predicted transmembrane domains and 11 loops belongs to the SUT1 clade. Heterologous expression of LcSUT1 in yeast proved that it was a functional sucrose transporter. Tissue-specific expression analysis showed that LcSUT1 was highly expressed in leaf and leaf sheath. The expression level of LcSUT1 was significantly up-regulated in leaf sheath after defoliation, but was not induced by wound signal. Furthermore, the level of LcSUT1 expression increased in callus, a model sink tissue, when grew on N6 medium without sucrose. Taken together, our results revealed a novel mechanism in which the increased expression of LcSUT1 in leaf sheaths after defoliation was caused by sucrose starvation rather than by wound signal.
... The observation of stress-induced expression by a sucrose synthase gene implies that this gene may play a role in providing a supply of carbohydrates to cells involved in the wound response, which is not wholly unexpected as wounded tissues behave as sinks (reviewed by Ibraheem et al. 2008). Bioinformatic analysis of the wound-responsive-268 to-103 CsSUS1p fragment indicated the presence of several pathogen-induced cis-acting elements. ...
Interest in phloem-specific promoters for the engineering of transgenic plants has been increasing in recent years. In this study we isolated two similar, but distinct, alleles of the Citrus sinensis
sucrose synthase-1 promoter (CsSUS1p) and inserted them upstream of the β-glucuronidase (GUS) gene to test their ability to drive expression in the phloem of transgenic Arabidopsis
thaliana and Nicotiana tabacum. Although both promoter variants were capable of conferring localized GUS expression in the phloem, the CsSUS1p-2 allele also generated a significant level of expression in non-target tissues. Unexpectedly, GUS expression was also instigated in a minority of CsSUS1p::GUS lines in response to wounding in the leaves of transgenic Arabidopsis. Deletion analysis of the CsSUS1p suggested that a fragment comprising nucleotides −410 to −268 relative to the translational start site contained elements required for phloem-specific expression while nucleotides −268 to −103 contained elements necessary for wound-specific expression. Interestingly, the main difference between the two CsSUS1p alleles was the presence of a 94-bp insertion in allele 2. Fusion of this indel to a minimal promoter and GUS reporter gene indicated that it contained stamen and carpel-specific enhancer elements. This finding of highly specific and separable regulatory units within the CsSUS1p suggests that this promoter may have a potential application in the generation of constructs for the use in the development of transgenic plants resistant to a wide variety of target pests.
... EIRE has been found to occur in the promoter of diverse defense-related genes (Rushton et al., 1996) and have been generally linked to be involved in the induction of plant defense pathways. The presence of these motifs at the regulatory regions of OsSUT1 and OsSUT2 in rice; and AtSUC3, AtSUC4 and AtSUC7 in Arabidopsis, may infer that they are required for the import of photoassimilate into an infected cell/tissue to meet the sudden high cellular metabolic energy demand and changes experienced during pathogen infection (Ibraheem et al., 2008). The dehydration-responsive element (DRE) was identified in the regulatory region of all Arabidopsis sucrose transporter genes, except in AtSUC5. ...
The regulation of gene expression involves a multifarious regulatory system. Each gene contains a unique combination of cis-acting regulatory sequence elements in the 5' regulatory region that determines its temporal and spatial expression. Cis-acting regulatory elements are essential transcriptional gene regulatory units; they control many biological processes and stress responses. Thus a full understanding of the transcriptional gene regulation system will depend on successful functional analyses of cis-acting elements. Cis-acting regulatory elements present within the 5' regulatory region of the sucrose transporter gene families in rice (Oryza sativa Japonica cultivar-group) and Arabidopsis thaliana, were identified using a bioinformatics approach. The possible cis-acting regulatory elements were predicted by scanning 1.5kbp of 5' regulatory regions of the sucrose transporter genes translational start sites, using Plant CARE, PLACE and Genomatix Matinspector professional databases. Several cis-acting regulatory elements that are associated with plant development, plant hormonal regulation and stress response were identified, and were present in varying frequencies within the 1.5kbp of 5' regulatory region, among which are; A-box, RY, CAT, Pyrimidine-box, Sucrose-box, ABRE, ARF, ERE, GARE, Me-JA, ARE, DRE, GA-motif, GATA, GT-1, MYC, MYB, W-box, and I-box. This result reveals the probable cis-acting regulatory elements that possibly are involved in the expression and regulation of sucrose transporter gene families in rice and Arabidopsis thaliana during cellular development or environmental stress conditions.
... Glycoside hydrolases are involved in cell wall polysaccharide metabolism, biosynthesis and remodulation of glycans, mobilization of energy during symbiosis, signaling and stress induced secondary plant metabolism [60]. Sugar transporters play a direct role in signal transduction by regulating sugar transport during normal as well as pathogen or wound -induced stressful conditions [61,62,63]. In our study, the expression of ESTs sharing homology with sugar cleaving enzymes and sugar transporters emphasized the role of the fungus in inciting the host defense machinery for protecting the foodprocessing unit. ...
Biotrophic interaction between host and pathogen induces generation of reactive oxygen species that leads to programmed cell death of the host tissue specifically encompassing the site of infection conferring resistance to the host. However, in the present study, biotrophic relationship between Fusarium oxysporum and chickpea provided some novel insights into the classical concepts of defense signaling and disease perception where ROS (reactive oxygen species) generation followed by hypersensitive responses determined the magnitude of susceptibility or resistant potentiality of the host.
Microscopic observations detected wound mediated in planta pathogenic establishment and its gradual progression within the host vascular tissue. cDNA-AFLP showed differential expression of many defense responsive elements. Real time expression profiling also validated the early recognition of the wound inducing pathogen by the host. The interplay between fungus and host activated changes in primary metabolism, which generated defense signals in the form of sugar molecules for combating pathogenic encounter.
The present study showed the limitations of hypersensitive response mediated resistance, especially when foreign encounters involved the food production as well as the translocation machinery of the host. It was also predicted from the obtained results that hypersensitivity and active species generation failed to impart host defense in compatible interaction between chickpea and Fusarium. On the contrary, the defense related gene(s) played a critical role in conferring natural resistance to the resistant host. Thus, this study suggests that natural selection is the decisive factor for selecting and segregating out the suitable type of defense mechanism to be undertaken by the host without disturbing its normal metabolism, which could deviate from the known classical defense mechanisms.
... During this period, leaf photoassimilates are formed and transported mainly in the form of sucrose (Lalonde et al. 2004; Lbraheem et al. 2008; Lemoine 2000; Reynolds et al. 2012; Xiong et al. 1994), therefore maintaining a high leaf photosynthetic capacity and adequate supply of sugar is advantageous for improving yield. The synthesis and accumulation of starch is closely related to the crop yield as starch accounts for approximately 70 % of the total dry weight of grains (Awika 2011; Jiang et al. 2002a, b, c). ...
Glycine betaine (GlyBet), a quaternary ammonium compound, functions as an osmoprotectant in many organisms including plants. Previous research has shown that over-expression of enzymes for GlyBet biosynthesis in transgenic plants improved abiotic stress tolerance, but so far no study on the effects of plastid-expression of choline monooxygenase, the enzyme that catalyzes the conversion of choline into betaine aldehyde, has been reported. In the present study, tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants were transformed with a gene for choline monooxygenase (BvCMO) from beet (Beta vulgaris) via plastid genetic engineering. Transplastomic plants constitutively expressing BvCMO under the control of the ribosomal RNA operon promoter and a synthetic T7 gene G10 leader were able to accumulate GlyBet in leaves, roots and seeds, and exhibited improved tolerance to toxic level of choline and to salt/drought stress when compared to wild type plants. Transplastomic plants also demonstrated higher net photosynthetic rate and apparent quantum yield of photosynthesis in the presence of 150 mM NaCl. Salt stress caused no significant change on the maximal efficiency of PSII photochemistry (Fv/Fm) in both wild type and transplastomic plants, but a decrease in the actual efficiency of PSII (PhiPSII) was observed, and such a decrease was much greater in wild type plants. Our results demonstrate the feasibility of improving salt and drought tolerance in plants through plastid transformation with BvCMO gene.
