Rewatering Treatment Research Articles

Embolized Stems Recover Overnight in Zea mays: The Role of Soil Water, Root Pressure, and Nighttime Transpiration.

It is not currently well-understood how much xylem conductance is lost in maize plants during the day, if conductance is recovered during the night, or what soil water conditions are required for recovery to take place. To answer these questions we designed a greenhouse experiment whereby two genetically dissimilar maize genotypes were subjected to a level of water stress commonly experienced in the field (Ψxylem ∼-2 MPa). We then measured the loss of stem-specific conductivity associated with this level of stress, as well as the overnight recovery following three re-watering treatments: Ψsoil ∼ 0 MPa, Ψsoil ∼-0.40 MPa, and Ψsoil ∼-1.70 MPa. Mid-day leaf water potentials of -1.98 MPa resulted in stem-specific conductivity (KS) values that were 31.5% of maximal (i.e., 68% loss). Returning soils to field capacity (Ψsoil ∼ 0 MPa) overnight allowed for the significant recovery of KS (76% of maximal), whereas partial watering (Ψsoil ∼-0.40 MPa) resulted KS values that were 51.7% of maximal values, whereas not watering resulted in no recovery (35.4% of maximal; Ψsoil ∼-1.7 MPa). Recovery of KS was facilitated by the generation of root pressure and low rates of nighttime transpiration.

Single-base resolution methylomes of upland cotton (Gossypium hirsutum L.) reveal epigenome modifications in response to drought stress

BackgroundDNA methylation, with a cryptic role in genome stability, gene transcription and expression, is involved in the drought response process in plants, but the complex regulatory mechanism is still largely unknown.ResultsHere, we performed whole-genome bisulfite sequencing (WGBS) and identified long non-coding RNAs on cotton leaves under drought stress and re-watering treatments. We obtained 31,223 and 30,997 differentially methylated regions (representing 2.48% of the genome) after drought stress and re-watering treatments, respectively. Our data also showed that three sequence contexts, including mCpG, mCHG, mCHH, all presented a hyper-methylation pattern under drought stress and were nearly restored to normal levels after the re-watering treatment. Among all the methylation variations, asymmetric CHH methylation was the most consistent with external environments, suggesting that methylation/demethylation in a CHH context may constitute a novel epigenetic modification in response to drought stress. Combined with the targets of long non-coding RNAs, we found that long non-coding RNAs may mediate variations in methylation patterns by splicing into microRNAs. Furthermore, the many hormone-related genes with methylation variations suggested that plant hormones might be a potential mechanism in the drought response.ConclusionsFuture crop-improvement strategies may benefit by taking into account not only the DNA genetic variations in cotton varieties but also the epigenetic modifications of the genome.

Differentially Methylated Epiloci Generated from Numerous Genotypes of Contrasting Tolerances Are Associated with Osmotic-Tolerance in Rice Seedlings

DNA methylation plays an essential role in plant responses to environmental stress. Since drought develops into a rising problem in rice cultivation, investigations on genome-wide DNA methylation in responses to drought stress and in-depth explorations of its association with drought-tolerance are required. For this study, 68 rice accessions were used for an evaluation of their osmotic-tolerance related to 20% PEG6000 simulated physiological traits. The tolerant group revealed significantly higher levels of total antioxidant capacity and higher contents of H2O2 in both normal and osmotic-stressed treatments, as well as higher survival ratios. We furthermore investigated the DNA methylation status in normal, osmotic-stressed, and re-watering treatments via the methylation-sensitive amplification polymorphism (MSAP). The averaged similarity between two rice accessions from tolerant and susceptible groups was approximately 50%, similar with that between two accessions within the tolerant/susceptible group. However, the proportion of overall tolerance-associated epiloci was only 5.2% of total epiloci. The drought-tolerant accessions revealed lower DNA methylation levels in the stressed condition and more de-methylation events when they encountered osmotic stress, compared to the susceptible group. During the recovery process, the drought-tolerant accessions possessed more re-methylation events. Fourteen differentially methylated epiloci (DME) were, respectively, generated in normal, osmotic-stressed, and re-watering treatments. Approximately, 35.7% DME were determined as tolerance-associated epiloci. Additionally, rice accessions with lower methylation degrees on DME in the stressed conditions had a higher survival ratio compared to these with higher methylation degrees. This result is consistent with the lower DNA methylation levels of tolerant accessions observed in the stressed treatment. Methylation degrees on a differentially methylated epilocus may further influence gene regulation in the rice seedling in response to the osmotic stress. All these results indicate that DME generated from a number of genotypes could have higher probabilityies for association with stress-tolerance, rather than DME generated from two genotypes of contrasting tolerance. The DME found in this study are suspected to be good epigenetic markers for the application in drought-tolerant rice breeding. They could also be a valuable tool to study the epigenetic differentiation in the drought-tolerance between upland and lowland rice ecotypes.

Integrated mRNA and microRNA analysis identifies genes and small miRNA molecules associated with transcriptional and post-transcriptional-level responses to both drought stress and re-watering treatment in tobacco

BackgroundDrought stress is one of the most severe problem limited agricultural productivity worldwide. It has been reported that plants response to drought-stress by sophisticated mechanisms at both transcriptional and post-transcriptional levels. However, the precise molecular mechanisms governing the responses of tobacco leaves to drought stress and water status are not well understood. To identify genes and miRNAs involved in drought-stress responses in tobacco, we performed both mRNA and small RNA sequencing on tobacco leaf samples from the following three treatments: untreated-control (CL), drought stress (DL), and re-watering (WL).ResultsIn total, we identified 798 differentially expressed genes (DEGs) between the DL and CL (DL vs. CL) treatments and identified 571 DEGs between the WL and DL (WL vs. DL) treatments. Further analysis revealed 443 overlapping DEGs between the DL vs. CL and WL vs. DL comparisons, and, strikingly, all of these genes exhibited opposing expression trends between these two comparisons, strongly suggesting that these overlapping DEGs are somehow involved in the responses of tobacco leaves to drought stress. Functional annotation analysis showed significant up-regulation of genes annotated to be involved in responses to stimulus and stress, (e.g., late embryogenesis abundant proteins and heat-shock proteins) antioxidant defense (e.g., peroxidases and glutathione S-transferases), down regulation of genes related to the cell cycle pathway, and photosynthesis processes. We also found 69 and 56 transcription factors (TFs) among the DEGs in, respectively, the DL vs. CL and the WL vs. DL comparisons. In addition, small RNA sequencing revealed 63 known microRNAs (miRNA) from 32 families and 368 novel miRNA candidates in tobacco. We also found that five known miRNA families (miR398, miR390, miR162, miR166, and miR168) showed differential regulation under drought conditions. Analysis to identify negative correlations between the differentially expressed miRNAs (DEMs) and DEGs revealed 92 mRNA-miRNA interactions between CL and DL plants, and 32 mRNA-miRNA interactions between DL and WL plants.ConclusionsThis study provides a global view of the transcriptional and the post-transcriptional responses of tobacco under drought stress and re-watering conditions. Our results establish an empirical foundation that should prove valuable for further investigations into the molecular mechanisms through which tobacco, and plants more generally, respond to drought stress at multiple molecular genetic levels.

Genome-Wide Analysis of Long Noncoding RNAs and Their Responses to Drought Stress in Cotton (Gossypium hirsutum L.).

Recent researches on long noncoding RNAs (lncRNAs) have expanded our horizon of gene regulation and the cellular complexity. However, the number, characteristics and expression patterns of lncRNAs remain poorly characterized and how these lncRNAs biogenesis are regulated in response to drought stress in cotton are still largely unclear. In the study, using a reproducibility-based RNA-sequencing and bioinformatics strategy to analyze the lncRNAs of 9 samples under three different environment stresses (control, drought stress and re-watering, three replications), we totally identified 10,820 lncRNAs of high-confidence through five strict steps filtration, of which 9,989 were lincRNAs, 153 were inronic lncRNAs, 678 were anti-sense lncRNAs. Coding function analysis showed 6,470 lncRNAs may have the ability to code proteins. Small RNAs precursor analysis revealed that 196 lncRNAs may be the precursors to small RNAs, most of which (35.7%, 70) were miRNAs. Expression patterns analysis showed that most of lncRNAs were expressed at a low level and most inronic lncRNAs (75.95%) had a consistent expression pattern with their adjacent protein-coding genes. Further analysis of transcriptome data uncovered that lncRNAs XLOC_063105 and XLOC_115463 probably function in regulating two adjacent coding genes CotAD_37096 and CotAD_12502, respectively. Investigations of the content of plant hormones and proteomics analysis under drought stress also complemented the prediction. We analyzed the characteristics and the expression patterns of lncRNAs under drought stress and re-watering treatment, and found lncRNAs may be likely to involve in regulating plant hormones pathway in response to drought stress.

Comparative proteomics analyses of intraspecific differences in the response of Stipa purpurea to drought

Stipa purpurea is widely distributed along a large precipitation gradient on the Tibetan Plateau. This implies that S. purpurea from different populations may have different responses to drought stress. To explore this we compared the morphological and physiological changes of S. purpurea seedlings cultivated from seeds from Gar County and Nagqu County after 7 and 14 days of drought stress and subsequent re-watering. The results showed that S. purpurea plants from the more arid Gar area were more tolerant to drought stress than that from Nagqu. To investigate the potential mechanisms underlying this difference, we used iTRAQ quantitative proteomics technology to analyze protein dynamics in S. purpurea samples treated with 7 days of drought stress and subsequent re-watering. The results indicated that, during the process of drought and re-watering treatments, there were differentially expressed proteins in either or both S. purpurea populations. These differential proteins were divided into 24 functional categories that were mainly associated with stress response, the antioxidant system, photosynthesis, carbohydrate metabolism, and post-translational modifications. According to these results, we concluded that the molecular basis of stronger drought resistance likely lies in the specific up-regulation or higher expression of many proteins involved in stress response, the antioxidant system, post-translational modification and osmotic regulation in S. purpurea from Gar County compared with that from Nagqu. This study improves our understanding of the intraspecific differences in drought resistance within S. purpurea populations, which helps to understand the distribution of S. purpurea along the moisture gradient, as well as the effect of climate change on this species.

Transcriptome Profiling of the Potato (Solanum tuberosum L.) Plant under Drought Stress and Water-Stimulus Conditions.

Drought stress can seriously affect tuberization, yield and quality of potato plant. However, the precise molecular mechanisms governing potato stolon’s response to drought stress and water supply are not very well understood. In this work, a potato (Solanum tuberosum L.) variant, Ningshu 4, was subjected to severe drought stress treatment (DT) and re-watering treatment (RWT) at tuber bulking stage. Strand-specific cDNA libraries of stolon materials were constructed for paired-end transcriptome sequencing analyses and differentially expressed gene (DEG) examination. In comparison to untreated-control (CT) plants, 3189 and 1797 DEGs were identified in DT and RWT plants and 4154 solely expressed DEGs were screened out from these two comparison groups. Interestingly, 263 genes showed opposite expression patterns in DT and RWT plants. Among them, genes homologous to Protein Phosphatase 2C (PP2C), Aspartic protease in guard cell 1 (ASPG1), auxin-responsive protein, Arabidopsis pseudo response regualtor 2 (APRR2), GA stimulated transcripts in Arabidopsis 6 (GASA6), Calmodulin-like protein 19 (CML19), abscisic acid 8'-hydroxylases and calcium-transporting ATPase, et al. were related with drought-stress and water stimulus response. Sixteen DEGs involved in starch synthesis, accumulation and tuber formation exhibited significantly different expression upon re-watering. In addition, 1630, 1527 and 1596 transcription factor encoding genes were detected in CT, DT and RWT. DEGs of ERF, bHLH, MYB, NAC, WRKY, C2H2, bZIP and HD-ZIP families accounted for 50% in three comparison groups, respectively. Furthermore, characteristics of 565 gene ontology (GO) and 108 Kyoto Encyclopedia of Genes and Genomes pathways (KEGG) were analyzed with the 4154 DEGs. All these results suggest that the drought- and water-stimulus response could be implemented by the regulated expression of metabolic pathway DEGs, and these genes were involved in the endogenous hormone biosynthesis and signal transduction pathways. Our data provide more direct information for future study on the interaction between key genes involved in various metabolic pathways under drought stress in potato.

Enhanced drought tolerance in transgenic rice over-expressing of maize C4 phosphoenolpyruvate carboxylase gene via NO and Ca2+

We determined the effects of endogenous nitric oxide and Ca2+ on photosynthesis and gene expression in transgenic rice plants (PC) over-expressing the maize C4pepc gene, which encodes phosphoenolpyruvate carboxylase (PEPC) under drought. In this study, seedlings were subjected to PEG 6000 treatments using PC and wild type (WT; Kitaake). The results showed that, compared with WT, PC had higher relative water content (RWC) and net photosynthetic rate (Pn) under drought. During a 2-day re-watering treatment, Pn recovered faster in PC than in WT. Further analyses showed that, under the drought treatment, the amount of endogenous hydrogen peroxide (H2O2) increased in WT mainly via NADPH oxidase. While in PC, the endogenous nitric oxide (NO) content increased via nitrate reductase and nitric oxide synthase on day 2 of the drought treatment and day 1 of the re-watering treatment. After 2 days of drought treatment, PC also showed higher PEPC activity, calcium content, phospholipase D (PLD) activity, C4-pepc and NAC6 transcript levels, and protein kinase activity as compared with PC without treatment. These changes did not occur in WT. Correlation analysis also proved NO associated with these indicators in PC. Based on these results, there was a particular molecular mechanism of drought tolerance in PC. The mechanism is related to the signaling processes via NO and Ca2+ involving the protein kinase and the transcription factor, resulted in up-regulation of PEPC activity and its gene expression, such as C4pepc. Some genes encode antioxidant system, cu/zn-sod as well, which promote antioxidant system to clear MDA and superoxide anion radical, thereby conferring drought tolerance.

Over-expression of OsHsfA7 enhanced salt and drought tolerance in transgenic rice

Heat shock proteins play an important role in plant stress tolerance and are mainly regulated by heat shock transcription factors (Hsfs). In this study, we generated transgenic rice over-expressing OsHsfA7 and carried out morphological observation and stress tolerance assays. Transgenic plants exhibited less, shorter lateral roots and root hair. Under salt treatment, over-expressing OsHsfA7 rice showed alleviative appearance of damage symptoms and higher survival rate, leaf electrical conductivity and malondialdehyde content of transgenic plants were lower than those of wild type plants. Meanwhile, transgenic rice seedlings restored normal growth but wild type plants could not be rescued after drought and re-watering treatment. These findings indicate that over-expression of OsHsfA7 gene can increase tolerance to salt and drought stresses in rice seedlings. [BMB Reports 2013; 46(1): 31-36]

Regulation of the ascorbate-glutathione cycle in wild almond during drought stress

In wild species of almond (Prunus spp.), the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), as well as the levels of ascorbate/glutathione pools and H2O2 were subjected to water deficit and shade conditions. After 60 days of water shortage, the species were subjected to a rewatering treatment. During water recovery, leaves exposed to sunlight and leaves under shade conditions of about 20–35% of environmental irradiance were sampled. After 70 days without irrigation, mean predawn leaf water potential of all the species fell from −0.32 to −2.30 MPa and marked decreases in CO2 uptake and transpiration occurred. The activities of APX, MDHAR, DHAR, and GR increased in relation to the severity of drought stress in all the wild species studied. Generally, APX, MDHAR, DHAR, and GR were down-regulated during the rewatering phase and their activities decreased faster in shaded leaves than in sun-exposed leaves. The levels in total ascorbate, glutathione, and H2O2 were directly related to the increase in drought stress and subsequently decreased during rewatering. The antioxidant response of wild almond species to drought stress limits cellular damage caused by reactive oxygen species during periods of water deficit and may be of key importance for the selection of drought-resistant rootstocks for cultivated almond.

Differences in drought sensitivities and photosynthetic limitations between co-occurring C3 and C4 (NADP-ME) Panicoid grasses.

The success of C4 plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C4 grasses are not necessarily less sensitive to drought than C3 grasses and are proposed to respond with greater metabolic limitations, while the C3 response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C3 and C4 NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response. Six species of locally co-occurring grasses, C3) species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C4 (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO2 concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types. Leaves of C4 species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C4 photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO2 assimilation, whereas, in the C3 species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C4 plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C3 plants which recovered a greater proportion of photosynthesis through increased stomatal conductance. Within the Panicoid grasses, C4 (NADP-ME) species are metabolically more sensitive to drought than C3 species and recover more slowly from drought.

Carbon Metabolism and Bacteroid Functioning Are Involved in the Regulation of Nitrogen Fixation inMedicago truncatulaUnder Drought and Recovery

Regulation of symbiotic nitrogen fixation (SNF) during drought stress is complex and not yet fully understood. In the present work, the involvement of nodule C and N metabolism in the regulation of SNF in Medicago truncatula under drought and a subsequent rewatering treatment was analyzed using a combination of metabolomic and proteomic approaches. Drought induced a reduction of SNF rates and major changes in the metabolic profile of nodules, mostly an accumulation of amino acids (Pro, His, and Trp) and carbohydrates (sucrose, galactinol, raffinose, and trehalose). This accumulation was coincidental with a decline in the levels of bacteroid proteins involved in SNF and C metabolism, along with a partial reduction of the levels of plant sucrose synthase 1 (SuSy1). In contrast, the variations in enzymes related to N assimilation were found not to correlate with the reduction in SNF, suggesting that these enzymes do not have a role in the regulation of SNF. Unlike the situation in other legumes such as pea and soybean, the drought-induced inhibition of SNF in M. truncatula appears to be caused by impairment of bacteroid metabolism and N(2)-fixing capacity rather than a limitation of respiratory substrate.

Drought Stress Alters Water Relations and Expression of PIP-Type Aquaporin Genes in Nicotiana tabacum Plants

Plasma membrane intrinsic proteins (PIPs), a type of aquaporins, mediate water transport in many plant species. In this study, we investigated the relationship between the functions of PIP-type water channels and water relations of tobacco plants (Nicotiana tabacum cv. Samsun) under drought stress. Drought stress treatments have led to reductions in the stomatal conductance, transpiration, water potential and turgor pressure in leaves, and also the sap flow rate and osmotic hydraulic conductance in roots. In contrast, leaf osmotic pressure was increased in response to drought stress. Interestingly, the accumulation of NtPIP1;1 and NtPIP2;1 transcripts was significantly decreased, but only that of the NtAQP1 transcript was increased under drought stress. Functional analysis using Xenopus laevis oocytes revealed that NtPIP2;1 shows marked water transport activity, but the activities of NtAQP1 and NtPIP1;1 are weak or almost negligible, respectively, when expressed alone. However, co-expression of NtPIP1;1 with NtPIP2;1 significantly enhanced water transport activity compared with that of NtPIP1;1- or NtPIP2;1-expressing oocytes, suggesting that these two aquaporins may function as a water channel, forming a heterotetramer. Heteromerization of NtPIP1;1 and NtPIP2;1 was also suggested by co-expression analyses of NtPIP1;1-GFP (green fluorescent protein) and NtPIP2;1 in Xenopus oocytes. Re-watering treatments recovered water relation parameters and the accumulation of the three NtPIP transcripts to levels similar to control conditions. These results suggest that NtPIP1;1 and NtPIP2;1 play an important role in water transport in roots, and that expression of NtPIP1;1 and NtPIP2;1 is down-regulated in order to reduce osmotic hydraulic conductance in the roots of tobacco plants under drought stress.

Corrigendum

New PhytologistVolume 175, Issue 4 p. 792-792 Free Access Corrigendum This article corrects the following: Photosynthetic limitations in response to water stress and recovery in Mediterranean plants with different growth forms Jeroni Galmés, Hipólito Medrano, Jaume Flexas, Volume 175Issue 1New Phytologist pages: 81-93 First Published online: April 23, 2007 First published: 06 August 2007 https://doi.org/10.1111/j.1469-8137.2007.02198.xCitations: 1AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat New Phytologist 175 (2007), 81–93 Since its publication, the authors of Galmés et al. (2007) have brought to our attention an error in the units on the y-axis label to Fig. 3(c). The label should read: gi (mol CO2 m−2 s−1). The correct figure is printed below. Figure 3Open in figure viewerPowerPoint Relationship between stomatal conductance (gs) and (a) net photosynthetic rate (AN); (b) electron transport rate (ETR); (c) mesophyll conductance (gi); (d) maximum rate of carboxylation (Vc,max). Values from rewatering treatment are not included. Regression coefficients and significance of each relationship are shown. Values are means ± SE of four to five replicates per species and treatment. Symbols and species: •, Diplotaxis ibicensis; ○, Beta maritima ssp. marcosii; □, B. maritima ssp. maritima; ▪, Limonium magallufianum; ▵, Limonium gibertii; ▴, Phlomis italica; ▾, Lavatera maritima; ▿, Cistus albidus; ◆, Hypericum balearicum; ◊, Pistacia lentiscus. We apologize to our readers for this mistake. Reference Galmés J, Medrano H, Flexas J. 2007. Photosynthetic limitations in response to water stress and recovery in Mediterranean plants with different growth forms. New Phytologist 175: 81– 93. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Citing Literature Volume175, Issue4September 2007Pages 792-792 FiguresReferencesRelatedInformation

Photosynthesis of Rehmannia glutinosa subjected to drought stress is enhanced by choline chloride through alleviating lipid peroxidation and increasing proline accumulation

Rehmannia glutinosa seedlings were pretreated with choline chloride (CC) in concentrations of 0, 0.7, 2.1 and 3.5 mM, and then subjected to drought and rewatering treatment to study the effects of CC on the generation of reactive oxygen species (O 2 − , H2O2), lipid peroxidation, proline accumulation, water status and photosynthesis. The results showed that pretreatment with CC alleviated the inhibition of SOD and APX activity caused by drought stress, and therefore, the rate of O 2 − production and H2O2 concentration were reduced and lipid peroxidation decreased in pretreated plants. CC pretreatment also accelerated accumulation of proline, maintained higher Ψw and RWC, deferred leaf water loss during drought stress and retarded the drop in proline concentration after rewatering. Consequently, drought-induced decreases in Fm/F0, Fv/Fm, ΦPS2, qP, and A and increase in qNP were inhibited and the recovery of photosynthesis after rewatering was quicker in pretreated plants. Although differences in Fv/Fm, ΦPS2 and qP between treatments were not significant, there was a general trend that the effects of CC increased with the rise of its concentrations. The data suggested that 2.1 mM of CC be suitable for alleviating lipid peroxidation, promoting proline accumulation, retarding leaf water loss and improving photosynthesis of R. glutinosa seedlings under drought stress.

Induction of xylem sap methylglycine by a drought and rewatering treatment and its inhibitory effects on the growth and development of plant organs

In higher plants, the xylem vessels functionally connect the roots with the above‐ground organs. The xylem sap transports various organic compounds, such as proteins and amino acids. We examined drought and rewatering‐inducible changes in the amino acid composition of root xylem sap collected from Cucurbita maxima roots. The major free amino acids in C. maxima root xylem sap were methylglycine (MeGly; sarcosine) and glutamine (Gln), but MeGly was not detected in the xylem sap of cucumber. MeGly is an intermediate compound in the metabolism of trimethylglycine (TMG; betaine), but its physiological effects in plants are unknown. Drought and rewatering treatment resulted in an increase in the concentration of MeGly in root xylem sap to 2.5 mM. After flowering, the MeGly concentration in the xylem sap dropped significantly, whereas the concentration of Gln decreased only after fruit ripening. One milli molar MeGly inhibited the formation of adventitious roots and their elongation in C. maxima, but glycine, dimethylglycine, or TMG had no effect. Similar effects and the inhibition of stem elongation were observed in shoot cuttings of cucumber and Phaseolus angularis. These observations seem to imply a possible involvement of xylem sap MeGly in the physiological responses of C. maxima plants to drought stress.

Influence of water deficit and rewatering on the components of the ascorbate–glutathione cycle in four interspecific Prunus hybrids

The activities of ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2), as well as the levels of ascorbate pool, glutathione pool and H 2O 2 were studied in plants of four interspecific Prunus hybrids subjected to water deficit and shade conditions. After 70 days of water shortage, plants were subjected to a rewatering treatment. During water recovery, leaves fully exposed to sunlight and leaves in shade conditions of about 30% of environmental irradiance were sampled. After 70 days without irrigation, mean pre-dawn leaf water potential of all the hybrids fell from −0.34 to −3.30 MPa and marked decreases in net photosynthesis and transpiration occurred. The activities of APX, MDHAR, DHAR and GR increased in relation to the severity of drought stress in all the clones studied. Generally, APX, MDHAR, DHAR and GR were down-regulated during the rewatering phase and their activities decreased faster in shaded leaves than in non-shaded leaves. The levels of total ascorbate, total glutathione and H 2O 2 were directly related to the increase of drought stress and subsequently decreased during rewatering. This response could limit cellular damage caused by active oxygen species during periods of water deficit. The ability of Prunus hybrids to regulate the enzymatic antioxidant system during different water and irradiance conditions might be an important attribute linked to drought tolerance.

Effects of different irradiance levels on some antioxidant enzymes and on malondialdehyde content during rewatering in olive tree

The effects of water recovery on the activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (POD; EC 1.11.1.7), polyphenol oxidase (PPO; EC 1.30.3.1) and lipoxygenase (LOX; EC 1.13.11.12), and on malondialdehyde (MDA) levels were investigated in 2-year-old Olea europaea L. (cv. “Coratina”) plants grown in environmental conditions characterized by high temperatures and irradiance levels and gradually subjected to a controlled water deficit. After reaching the maximum level of water stress, plants were subjected to a rewatering treatment for 30 days, under both environmental irradiance and semi-shade conditions. The activities of SOD, CAT, APX, POD and LOX, and MDA levels decreased during the rewatering period in both leaves and roots and these decrements were faster in plants rewatered in semi-shade conditions (SHP) than in plants under environmental light (NSHP). In contrast, PPO activity increased during rewatering in both leaf and root tissues. Thus, the lower expression of the enzymatic antioxidant system in SHP with respect to NSHP may be due to a reduced need of activated oxygen species removal. On the contrary, in NSHP, higher enzyme activities are required for a better protection against a more pronounced oxidative stress.

Root cortex death and subsequent initiation and growth of lateral roots from bare steles of chickpeas

The anatomical responses of chickpea (Cicer arietinum L.) roots to aging and severe water deficits and their capacity for subsequent initiation and growth of new lateral roots after rewatering are only partially known. This study was conducted to characterize the degeneration of epidermal and cortical cells of chickpea roots and the subsequent initiation and growth of new roots from bare steles, i.e., steles surrounded by an endodermis but lacking other parts of the cortex. Chickpea plants were grown in pots in a greenhouse under standard culture conditions (potting mix and daily watering) or drought treatments. For drought treatments, plants were grown in sand and exposed to repeated 10-d treatments of water deficits and rewatering. In standard culture conditions, older cortices collapsed and deteriorated but not simply as a function of chronological age. After one 10-d drought treatment, the epidermis and outer cortex of primary and some secondary and tertiary roots collapsed and after a subsequent rewatering treatment, the epidermis and cortex deteriorated and sloughed from steles. In both standard and drought conditions, bare steles were able to sustain growing root tips, indicating that the endodermis was effective in preserving stelar functions. In droughted plants, bare steles were able to initiate new lateral roots from the pericycle after rewatering, indicating that cortical tissue other than the endodermis was not necessary for secondary and tertiary chickpea roots to initiate new lateral roots. In a given root system exposed to the drought treatments, although the cortex collapsed on some roots, the cortices of other secondary roots did not collapse or deteriorate under similar severe conditions. The reason for cortical survival is unclear, but the response of these roots was similar to roots that have a suberized hypodermal layer which protects underlying cortical tissues from excessive drying. Key words: chickpea, Cicer arietinum L., drought, lateral roots, rewatering.

Ecophysiological Studies on the Drought Resistance of Soybean. I. Changes in photosynthesis, transpiration and root respiration with soil moisture deficit.

Two Korean cultivars (cv. Hwangkeumkong, Danyeobkong) and one Japanese cultivar (cv. Enrei) were grown in the same pot under glasshouse conditions to investigate the influence of water deficit on the photosynthetic rate, transpiration rate and root respiratory rate. The transpiration rate and stomatal conductance rapidly decreased with decreasing of soil moisture compared to the photosynthetic rate. Net photosynthesis remained at a high constant rate (>20 mg CO2 dm-2 h-1) during 4 days after non-watering treatment (pF1.9∼3.5), but at further treatment soil moisture deficit (over pF 3.5), net photosynthesis seriously decreased. These observed results were similar for all three cultivars. Different quadratic equations were obtained between net-photosynthetic rate and stomatal conductance, and a linear equation was obtained between transpiration rate and stomatal conductance in both periods of non-watering treatment and re-watering treatment. The photosynthetic and transpiration rates recovered to less than 67% and 49% of the previous levels, respectively. At prolonged suspension of water supply (41-46 days after emergence), a positive correlation was found between the root respiratory rate (25°C) and root nitrogen content. We also recognized that the rate of photosynthesis was significantly correlated with root respiration rate under water stress condition.