Leaf Water Loss Rate Research Articles

Wheat MIXTA-like Transcriptional Activators Positively Regulate Cuticular Wax Accumulation.

MIXTA-like transcription factors AtMYB16 and AtMYB106 play important roles in the regulation of cuticular wax accumulation in dicot model plant Arabidopsis thaliana, but there are very few studies on the MIXTA-like transcription factors in monocot plants. Herein, wheat MIXTA-like transcription factors TaMIXTA1 and TaMIXTA2 were characterized as positive regulators of cuticular wax accumulation. The virus-induced gene silencing experiments showed that knock-down of wheat TaMIXTA1 and TaMIXTA2 expressions resulted in the decreased accumulation of leaf cuticular wax, increased leaf water loss rate, and potentiated chlorophyll leaching. Furthermore, three wheat orthologous genes of ECERIFERUM 5 (TaCER5-1A, 1B, and 1D) and their function in cuticular wax deposition were reported. The silencing of TaCER5 by BSMV-VIGS led to reduced loads of leaf cuticular wax and enhanced rates of leaf water loss and chlorophyll leaching, indicating the essential role of the TaCER5 gene in the deposition of wheat cuticular wax. In addition, we demonstrated that TaMIXTA1 and TaMIXTA2 function as transcriptional activators and could directly stimulate the transcription of wax biosynthesis gene TaKCS1 and wax deposition gene TaCER5. The above results strongly support that wheat MIXTA-Like transcriptional activators TaMIXTA1 and TaMIXTA2 positively regulate cuticular wax accumulation via activating TaKCS1 and TaCER5 gene transcription.

Comprehensive Analysis of GH3 Gene Family in Potato and Functional Characterization of StGH3.3 under Drought Stress.

As an important hormone response gene, Gretchen Hagen 3 (GH3) maintains hormonal homeostasis by conjugating excess auxin with amino acids during plant stress-related signaling pathways. GH3 genes have been characterized in many plant species, but they are rarely reported in potato. Here, 19 StGH3 genes were isolated and characterized. Phylogenetic analysis indicated that StGH3s were divided into two categories (group I and group III). Analyses of gene structure and motif composition showed that the members of a specific StGH3 subfamily are relatively conserved. Collinearity analysis of StGH3 genes in potato and other plants laid a foundation for further exploring the evolutionary characteristics of the StGH3 genes. Promoter analysis showed that most StGH3 promoters contained hormone and abiotic stress response elements. Multiple transcriptome studies indicated that some StGH3 genes were responsive to ABA, water deficits, and salt treatments. Moreover, qRT-PCR analysis indicated that StGH3 genes could be induced by phytohormones (ABA, SA, and MeJA) and abiotic stresses (water deficit, high salt, and low temperature), although with different patterns. Furthermore, transgenic tobacco with transient overexpression of the StGH3.3 gene showed positive regulation in response to water deficits by increasing proline accumulation and reducing the leaf water loss rate. These results suggested that StGH3 genes may be involved in the response to abiotic stress through hormonal signal pathways. Overall, this study provides useful insights into the evolution and function of StGH3s and lays a foundation for further study on the molecular mechanisms of StGH3s in the regulation of potato drought resistance.

Leaf rolling precedes stomatal closure in rice (Oryza sativa) under drought conditions.

Leaf rolling is a physiological response to drought that may help to reduce water loss, but its significance as a contribution to drought tolerance is uncertain. We scored the leaf rolling of four rice genotypes along an experimental drought gradient using an improved cryo-microscopy method. Leaf water potential (Ψleaf), gas exchange, chlorophyll fluorescence, leaf hydraulic conductance, rehydration capacity, and the bulk turgor loss point were also analysed. During the drought process, stomatal conductance declined sharply to reduce water loss, and leaves rolled up before the stomata completely closed. The leaf water loss rate of rolled leaves was significantly reduced compared with artificially flattened leaves. The Ψleaf threshold of initial leaf rolling ranged from -1.95 to -1.04 MPa across genotypes. When a leaf rolled so that the leaf edges were touching, photosynthetic rate and stomatal conductance declined more than 80%. Across genotypes, leaf hydraulic conductance declined first, followed by gas exchange and chlorophyll fluorescence parameters. However, the Ψleaf threshold for a given functional trait decline differed significantly among genotypes, with the exception of leaf hydraulic conductance. Our results suggested that leaf rolling was mechanistically linked to drought avoidance and tolerance traits and might serve as a useful phenotypic trait for rice breeding in future drought scenarios.

Phenotypic Differences of Leaves and Transcriptome Analysis of Fraxinus mandshurica × Fraxinus sogdiana F1 Variety

Plant leaves, as one of the main organs of plants, have a crucial impact on plant development. In the hybrid F1 variety, one clone “1601” from the hybridization of Fraxinus mandshurica Rupr. × Fraxinus sogdiana Bunge was showed significant differences in leaf development with its female control “M8”. The leaf phenotypic differences of leaflets and fronds, photosynthesis parameters, rate of leaf water loss and leaf cell size were investigated between 1601 and M8. The leaf phenotypic details showed that the leaflets of 1601 were significantly smaller (leaflet size was 53.78% that of M8) and rounder (leaflet aspect ratio was 66.97% that of M8). Its leaflet margins were more serrated (the serrate number was 33.74% that of M8). The fronds of 1601 had more leaflets (1.17-fold that of M8) and shorter leaflet distance (73.44% that of M8). The photosynthetic heterosis was also significant (the net photosynthetic rate in 1601 was 1.43 times that of M8) and the rate of leaf water loss in 1601 was lower than M8. Meanwhile, the results of the leaf microstructure showed that the mesophyll cell area of M8 was smaller than 1601, indicating that the difference in leaf size was caused by the number of cells. To analyze the reasons for these differences in leaf phenotype and explore the important regulatory genes potentially involved in leaf development, the comparative transcriptome analysis of M8 and 1601 and weighted gene coexpression network analysis (WGCNA) were completed. The results showed that hormones, such as auxins and brassinolides (BRs), along with the transcription factors (TFs), such as the growth-regulating factors (GRFs) and TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATION CELL FACTOR (TCPs), play essential roles in the difference of leaf size between 1601 and M8 by regulating cell proliferation. These data further shed light on the developmental mechanisms of the leaves of F. mandshurica.

Sea-island cotton (Gossypium barbadense L.) GbTCP5 improves plant adaptation to drought and salt stress by directly activating GbERD7, GbUBC19, and GbGOLS2 expression

Cotton is one of the most important cash crops in the world. Most of its production areas are in arid or semiarid regions, and drought and salinity seriously affect cotton production. Plant teosinte branched1/cycloidea/proliferating cell factor 1 (TCP) transcription factors play a pivotal role in abiotic stress responses. However, the role of TCPs in the abiotic stress response in cotton has not been fully elucidated. Here, the function of the GbTCP5 transcription factor in the responses to drought and salt stresses was identified. The expression of GbTCP5 was induced by drought, salt, and abscisic acid (ABA) treatments. The exposure of 35S:GbTCP5 transgenic Arabidopsis to drought stress increased its survival rate and ABA content and decreased its leaf water loss rate and malondialdehyde (MDA) content compared with those of the wild type (WT). In addition, the expression levels of the stress response genes AtCOR15, AtCOR414, AtRD29A, AtLTP4, and AtPUB22 and the ABA biosynthesis-related gene AtNCED3 were significantly higher in 35S:GbTCP5 transgenic lines than in the WT. The exposure of 35S:GbTCP5 transgenic Arabidopsis to salt stress accelerated its germination rate, increased its root length, survival rate and chlorophyll content, and decreased the MDA content compared with those of the WT. Under drought or salt stress, cotton with virus-induced gene silencing of GbTCP5 showed a decreased survival rate, a shorter root length, a smaller root area, a reduced root volume and a higher MDA content compared with pTRV2 cotton. Transcriptome sequencing results confirmed that GbTCP5 was involved in several abiotic stress-related metabolic pathways. The results confirmed that GbTCP5 protein activated the expression of GbGLOS2, GbUBC19, and GbERD7 and then participated in the drought and salt tolerance of cotton by binding to the TCP cis-acting element in the promoter regions of these genes. All the above results prove that GbTCP5 plays a positive role in plant responses to drought and salt stress.

PhePLATZ1, a PLATZ transcription factor in moso bamboo (Phyllostachys edulis), improves drought resistance of transgenic Arabidopsis thaliana

Drought is one of the most serious environmental stresses. Plant AT-rich sequence and zinc-binding (PLATZ) proteins perform indispensable functions to regulate plant growth and development and to respond to environmental stress. In this present study, we identified PhePLATZ1 in moso bamboo and found that its expression was up-regulated in response to 20% PEG-6000 and abscisic acid (ABA) treatments. Next, transgenic PhePLATZ1-overexpressing Arabidopsis lines were generated. Overexpression of PhePLATZ1 improved drought stress resistance of transgenic plants by mediating osmotic regulation, enhancing water retention capacity and reducing membrane and oxidative damage. These findings were corroborated by analysing physiological indicators including chlorophyll, relative water content, leaf water loss rate, electrolyte leakage, H2O2, proline, malondialdehyde content and the enzyme activities of peroxidase and catalase. Subsequent seed germination and seedling root length experiments that included exposure to exogenous ABA treatments showed that ABA sensitivity decreased in transgenic plants relative to wild-type plants. Moreover, transgenic PhePLATZ1-overexpressing plants promoted stomatal closure in response to ABA treatment, suggesting that PhePLATZ1 might play a positive regulatory role in the drought resistance of plants via the ABA signaling pathway. In addition, the transgenic PhePLATZ1-OE plants showed altered expression of some stress-related genes when grown under drought conditions. Taken together, these findings improve our understanding of the drought response of moso bamboo and provide a key candidate gene for the molecular breeding of this species for drought tolerance.

Overexpression of GhABF3 increases cotton(Gossypium hirsutum L.) tolerance to salt and drought

BackgroundPlants suffer from various abiotic stresses during their lifetime, of which drought and salt stresses are two main factors limiting crop yield and quality. Previous studies have shown that abscisic acid (ABA) responsive element binding protein (AREB)/ ABRE binding factors (ABFs) in bZIP transcription factors are involved in plant stress response in an ABA-dependent manner. However, little is known about the properties and functions of AREB/ABFs, especially ABF3, in cotton.ResultsHere, we reported the cloning and characterization of GhABF3. Expression of GhABF3 was induced by drought,salt and ABA treatments. Silencing of GhABF3 sensitized cotton to drought and salt stress, which was manifested in decreased cellular antioxidant capacity and chlorophyll content. Overexpression of GhABF3 significantly improved the drought and salinity tolerance of Arabidopsis and cotton. Exogenous expression of GhABF3 resulted in longer root length and less leaf wilting under stress conditions in Arabidopsis thaliana. Overexpressing GhABF3 significantly improved salt tolerance of upland cotton by reducing the degree of cellular oxidation, and enhanced drought tolerance by decreasing leaf water loss rate. The increased expression of GhABF3 up-regulated the transcriptional abundance of downstream ABA-inducible genes under salt stress in Arabidopsis.ConclusionIn conclusion, our results demonstrated that GhABF3 plays an important role in plant drought and salt tolerance. Manipulation of GhABF3 by biotechnology might be an important strategy to alter the stress resistance of cotton.

Ubiquitin ligase OsRINGzf1 regulates drought resistance by controlling the turnover of OsPIP2;1.

SummaryWater is crucial for plant growth and survival. The transcellular water movement is facilitated by aquaporins (AQPs) that rapidly and reversibly modify water permeability. The abundance of AQPs is regulated by its synthesis, redistribution and degradation. However, the molecular mechanism of proteasomal degradation of AQPs remains unclear. Here, we demonstrate that a novel E3 ligase, OsRINGzf1, mediated the degradation of AQPs in rice. OsRINGzf1 is the candidate gene from a drought‐related quantitative trait locus (QTL) on the long arm of chromosome 4 in rice (Oryza sativa) and encodes a Really Interesting New Gene (RING) zinc finger protein 1. OsRINGzf1 possesses the E3 ligase activity, ubiquitinates and mediates OsPIP2;1 degradation, thus reducing its protein abundance. The content of OsPIP2;1 protein was decreased in OsRINGzf1 overexpression (OE) plants. The degradation of OsPIP2;1 was inhibited by MG132. The OsRINGzf1 OE plants, with higher leaf‐related water content (LRWC) and lower leaf water loss rate (LWLR), exhibited enhanced drought resistance, whereas the RNAi and knockout plants of OsRINGzf1 were more sensitive to drought. Together, our data demonstrate that OsRINGzf1 positively regulates drought resistance through promoting the degradation of OsPIP2;1 to enhance water retention capacity in rice.

A novel sweetpotato GATA transcription factor, IbGATA24, interacting with IbCOP9-5a positively regulates drought and salt tolerance

The GATA family is a group of zinc finger transcription factors that plays important roles in regulating developmental processes. However, the functions of GATA family members in the response of plants to drought and salt stress remain poorly studied. Here, we isolated a novel GATA gene ( IbGATA24 ) from sweetpotato. The expression of IbGATA24 was strongly induced by PEG6000, NaCl, and abscisic acid (ABA) treatments. IbGATA24 was located in the nucleus and exhibited no transactivation activity. IbGATA24 -overexpressing plants showed significantly enhanced tolerance to drought and salt stress. The leaf water loss rate and the leaf stomatal aperture of overexpression plants were significantly decreased. Genes involved in abscisic acid and jasmonic acid signaling pathways, and reactive oxygen species scavenging were up-regulated in transgenic plants under drought and salt treatments. The ABA, JA, and proline content and the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were significantly higher, and the accumulation of malondialdehyde (MDA) and H 2 O 2 was lower, in transgenic plants than in wild-type plants under stress conditions. IbGATA24 could interact with constitutive photomorphogenesis 9-5a (COP9-5a). Overexpression of IbCOP9-5a enhanced drought and salt stress resistance through regulating ABA and reactive oxygen species (ROS) accumulating. These results suggest that IbGATA24 interacting with IbCOP9-5a plays a positive regulatory role in abiotic stress tolerance. Our study identified a novel GATA transcription factor that could be used to improve the tolerance of sweetpotato and other plants to abiotic stress. • Expression of IbGATA24 is induced by multiple abiotic environmental stimuli. • IbGATA24 enhances hormone signaling pathway and ROS scavenging. • IbGATA24 interacting with IbCOP9-5a positively regulates drought and salt tolerance.

Ectopic Overexpression of Maize Heat Stress Transcription Factor ZmHsf05 Confers Drought Tolerance in Transgenic Rice.

Drought is a key factor affecting plant growth and development. Heat shock transcription factors (Hsfs) have been reported to respond to diverse abiotic stresses, including drought stress. In the present study, functional characterization of maize heat shock transcription factor 05 (ZmHsf05) gene was conducted. Homologous analysis showed that ZmHsf05 belongs to Class A2 Hsfs. The mRNA expression level of ZmHsf05 can be affected by drought, high temperature, salt, and abscisic acid (ABA) treatment. Ectopic overexpression of ZmHsf05 in rice (Oryza sativa) could significantly enhance the drought tolerance. Faced with drought stress, transgenic rice exhibited better phenotypic performance, higher survival rate, higher proline content, and lower leaf water loss rate, compared with wild-type plant Zhonghua11. Additionally, we assessed the agronomic traits of seven transgenic rice lines overexpressing ZmHsf05 and found that ZmHsf05 altered agronomical traits in the field trials. Moreover, rice overexpressing ZmHsf05 was more sensitive to ABA and had either a lower germination rate or shorter shoot length under ABA treatment. The transcription level of key genes in the ABA synthesis and drought-related pathway were significantly improved in transgenic rice after drought stress. Collectively, our results showed that ZmHsf05 could improve drought tolerance in rice, likely in an ABA-dependent manner.

Identification of HvLRX, a new dehydration and light responsive gene in Tibetan hulless barley (Hordeum vulgare var. nudum).

Tibetan hulless barley (Hordeum vulgare var. nudum), adjusting to the harsh environment on Qinghai-Tibet Plateau, is a good subject for analyzing drought tolerance mechanism. Several unannotated differentially expressed genes (DEGs) were identified through our previous RNA-Seq study using two hulless barley accessions with contrasting drought tolerance. One of these DEGs, HVU010048.2, showed up-regulated pattern under dehydration stress in both drought tolerant (DT) and drought susceptible (DS) accessions, while its function in drought resistance remains unknown. This new gene was named as HvLRX (light responsive X), because its expression was induced under high light intensity while suppressed under dark. To provide preliminary bioinformatics prediction, expression pattern, and drought resistance function of this new gene. Bioinformatics analysis of HvLRX were conducted by MEGA, PlantCARE, ProtParam, CELLO et al. The expression pattern of HvLRX under different light intensity, dehydration shock, gradual drought stress, NaCl stress, polyethylene glycol (PEG) 6000 stress and abscisic acid (ABA) treatment was investigated by quantitative reverse transcription-polymerase chain reaction (RT-qPCR). The function of HvLRX was analyzed by virus induced gene silencing (VIGS) in hulless barley and by transgenic method in tobacco. Full cDNAs of HvLRX were cloned and compared in three hulless barley accessions. Homologues of HvLRX protein in other plants were excavated and their phylogenetic relationship was analyzed. Several light responsive elements (ATC-motif, Box 4, G-box, Sp1, and chs-CMA1a) were identified in its promoter region. Its expression can be promoted under high light intensity, dehydration shock, gradual drought stress, PEG 6000, and NaCl stress, but was almost unchanged in ABA treatment. HvLRX-silenced plants had a higher leaf water loss rate (WLR) and a lower survival rate (SR) compared with controls under dehydration stress. The infected leaves of HvLRX-silenced plants lost their water content quickly and became withered at 10 dpi. The SR of HvLRX overexpressed transgenic tobacco plants was significantly higher than that of wild-type plants. These results indicated HvLRX play a role in drought resistance. Besides, retarded vegetative growth was detected in HvLRX-silenced hulless barley plants, which suggested that this gene is important for plant development. This study provided data of bioinformatics, expression pattern, and function of HvLRX. To our knowledge, this is the first report of this new dehydration and light responsive gene.

Exogenous hormones influence Brassica napus leaf cuticular wax deposition and cuticle function.

BackgroundCuticular waxes cover plant surface and play important roles in protecting plants from abiotic and biotic stresses. The variations of wax deposition and chemical compositions under changing environments have been shown to be related to plant adaptations. However, it is still not clear whether the wax depositions could be adjusted to increase plant adaptations to stressed conditions.MethodsIn this study, exogenous methyl jasmonate (MeJA), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and salicylic acid (SA) were applied to test their effects on cuticular wax deposition in two Brassica napus cultivars, Zhongshuang 9 (ZS9, low wax coverage ) and Yuyou 19 (YY19, high wax coverage). Next, we measured the water loss rate and the transcriptional expression of genes involved in wax biosynthesis as well as genes related to disease defense.ResultsSeven wax compound classes, including fatty acids, aldehydes, alkanes, secondary alcohols, ketones, and unbranched as well as branched primary alcohols, were identified in B. napus leaf wax mixtures. MeJA, SA and ACC treatments had no significant effect on total wax amounts in YY19, whereas ACC reduced total wax amounts in ZS9. Overall, hormone treatments led to an increase in the amounts of aldehydes and ketones, and a decrease of secondary alcohol in ZS9, whereas they led to a decrease of alkane amounts and an increase of secondary alcohol amounts in YY19. Concomitantly, both cultivars also exhibited different changes in cuticle permeability, with leaf water loss rate per 15 min increased from 1.57% (averaged across treatments) at 1.57% (averaged across treatments) at 15 min to 3.12% at 30 min for ZS9 (except for ACC treated plant) and decreased for YY19. MeJA-treated plants of both cultivars relatively had higher water loss rate per 15 min when compared to other treatments. Conclusion. Our findings that B. napus leaf wax composition and cuticle permeability are altered by exogenous SA, MeJA and ACC suggest that the hormone treatments affect wax composition, and that the changes in wax profiles would cause changes in cuticle permeability.

Weakened carbon and nitrogen metabolisms under post-silking heat stress reduce the yield and dry matter accumulation in waxy maize

Post-silking high temperature is one of the abiotic factors that affects waxy maize (Zea mays L. sinensis Kulesh) growth in southern China. We conducted a pot trial in 2016–2017 to study the effects of post-silking daytime heat stress (35°C) on the activities of enzymes involved in leaf carbon and nitrogen metabolisms and leaf reactive oxygen species (ROS) and water contents. This study could improve our understanding on dry matter accumulation and translocation and grain yield production. Results indicated that decreased grain number and weight under heat stress led to yield loss, which decreased by 20.8 and 20.0% in 2016 and 2017, respectively. High temperature reduced post-silking dry matter accumulation (16.1 and 29.5% in 2016 and 2017, respectively) and promoted translocation of pre-silking photoassimilates stored in vegetative organs, especially in leaf. The lower leaf water content and chlorophyll SPAD value, and higher ROS (H2O2 and O2−·) content under heat stress conditions indicated accelerated senescent rate. The weak activities of phosphoenolpyruvate carboxylase (PEPCase), Ribulose-1,5-bisphosphate carboxylase (RuBPCase), nitrate reductase (NR), and glutamine synthase (GS) indicated that leaf carbon and nitrogen metabolisms were suppressed when the plants suffered from a high temperature during grain filling. Correlation analysis results indicated that the reduced grain yield was mainly caused by the decreased leaf water content, weakened NR activity, and increased H2O2 content. The increased accumulation of grain weight and post-silking dry matter and the reduced translocation amount in leaf was mainly due to the increased chlorophyll SPAD value and NR activity. Reduced PEPCase and RuBPCase activities did not affect dry matter accumulation and translocation and grain yield. In conclusion, post-silking heat stress down-regulated the leaf NR and GS activities, increased the leaf water loss rate, increased ROS generation, and induced pre-silking carbohydrate translocation. However, it reduced the post-silking direct photoassimilate deposition, ultimately, leading to grain yield loss.

Genome-wide identification, structure characterization, and expression pattern profiling of aquaporin gene family in cucumber

BackgroundAquaporin (AQP) proteins comprise a group of membrane intrinsic proteins (MIPs) that are responsible for transporting water and other small molecules, which is crucial for plant survival under stress conditions including salt stress. Despite the vital role of AQPs, little is known about them in cucumber (Cucumis sativus L.).ResultsIn this study, we identified 39 aquaporin-encoding genes in cucumber that were separated by phylogenetic analysis into five sub-families (PIP, TIP, NIP, SIP, and XIP). Their substrate specificity was then assessed based on key amino acid residues such as the aromatic/Arginine (ar/R) selectivity filter, Froger’s positions, and specificity-determining positions. The putative cis-regulatory motifs available in the promoter region of each AQP gene were analyzed and results revealed that their promoter regions contain many abiotic related cis-regulatory elements. Furthermore, analysis of previously released RNA-seq data revealed tissue- and treatment-specific expression patterns of cucumber AQP genes (CsAQPs). Three aquaporins (CsTIP1;1, CsPIP2;4, and CsPIP1;2) were the most transcript abundance genes, with CsTIP1;1 showing the highest expression levels among all aquaporins. Subcellular localization analysis in Nicotiana benthamiana epidermal cells revealed the diverse and broad array of sub-cellular localizations of CsAQPs. We then performed RNA-seq to identify the expression pattern of CsAQPs under salt stress and found a general decreased expression level of root CsAQPs. Moreover, qRT-PCR revealed rapid changes in the expression levels of CsAQPs in response to diverse abiotic stresses including salt, polyethylene glycol (PEG)-6000, heat, and chilling stresses. Additionally, transient expression of AQPs in N. benthamiana increased leaf water loss rate, suggesting their potential roles in the regulation of plant water status under stress conditions.ConclusionsOur results indicated that CsAQPs play important roles in response to salt stress. The genome-wide identification and primary function characterization of cucumber aquaporins provides insight to elucidate the complexity of the AQP gene family and their biological functions in cucumber.

The Smaller the Leaf Is, the Faster the Leaf Water Loses in a Temperate Forest.

Leaf size (i.e., leaf surface area and leaf dry mass) profoundly affects a variety of biological carbon, water and energy processes. Therefore, the remarkable variability in individual leaf size and its trade-off with total leaf number in a plant have particularly important implications for understanding the adaption strategy of plants to environmental changes. The various leaf sizes of plants growing in the same habitat are expected to have distinct abilities of thermal regulation influencing leaf water loss and shedding heat. Here, we sampled 16 tree species co-occurring in a temperate forest in northeastern China to quantify the variation of leaf, stomata and twigs traits, and to determine the relationships of leaf size with leaf number and leaf water loss. We examined the right-skewed distributions of leaf size, leafing intensity, stomatal size and stomatal density across species. Leafing intensity was significantly negatively correlated with leaf size, accounting for 4 and 12% of variation in leaf area and leaf mass, respectively. Species was the most important factor in explaining the variation in leaf size (conditional R2 of 0.92 for leaf area and 0.82 for leaf mass). Leaf area and mass significantly increased with increasing diameter of twigs. Leaf water loss was strongly negatively correlated with leaf area and leaf mass during the first four hours of the measurement. Leaf area and leaf mass accounted for 38 and 30% of variation in total leaf water loss, respectively. Leaf water loss rate (k) was significantly different among tree species and markedly linearly decreased with increasing leaf area and leaf mass for simple-leaved tree species. In conclusion, the existence of a cross-species trade-off between the size of individual leaves and the number of leaves per yearly twig unit was confirmed in that temperate forest. There was strongly negative correlation between leaf water loss and leaf size across tree species, which provides evidences for leaf size in leaf temperature regulation in dry environment with strong radiation. The size-dependent leaf water relation is of central importance to recognize the functional role of leaf size in a changing climate including rapid changes in air temperature and rainfall.

Wheat bHLH-type transcription factor gene TabHLH1 is crucial in mediating osmotic stresses tolerance through modulating largely the ABA-associated pathway.

Wheat bHLH family gene TabHLH1 is responsive to drought and salt stresses, and it acts as one crucial regulator in mediating tolerance to aforementioned stresses largely through an ABA-associated pathway. Osmotic stresses are adverse factors for plant growth and crop productivity. In this study, we characterized TabHLH1, a gene encoding wheat bHLH-type transcription factor (TF) protein, in mediating plant adaptation to osmotic stresses. TabHLH1 protein contains a conserved basic-helix-loop-helix (bHLH) domain shared by its plant counterparts. Upon PEG-simulated drought stress, salt stress, and exogenous abscisic acid (ABA), the TabHLH1 transcripts in roots and leaves were induced. Under PEG-simulated drought stress and salt stress treatments, the tobacco seedlings with TabHLH1 overexpression exhibited improved growth and osmotic stress-associated traits, showing increased biomass and reduced leaf water loss rate (WLR) relative to wild type (WT). The transgenic lines also possessed promoted stomata closure under drought stress, salt stress, and exogenous ABA and increased proline and soluble sugar contents and reduced hydrogen peroxide (H2O2) amount under osmotic stress conditions, indicating that TabHLH1-mediated osmolyte accumulation and cellular ROS homeostasis contributed to the drought stress and salt stress tolerance. NtPYL12 and NtSAPK2;1, the genes encoding ABA receptor and SnRK2 family kinase, respectively, showed up-regulated expression in lines overexpressing TabHLH1 under osmotic stress and exogenous ABA conditions; overexpression of them conferred plants modified stomata movement, leaf WLR, and growth feature under drought and high salinity, suggesting that these ABA-signaling genes are mediated by wheat TabHLH1 gene and involved in regulating plant responses to simulated drought and salt stresses. Our investigation indicates that the TabHLH1 gene plays critical roles in plant tolerance to osmotic stresses largely through an ABA-dependent pathway.

Different allocation of carbohydrates and phenolics in dehydrated leaves of triticale

Carbohydrates are used in plant growth processes, osmotic regulation and secondary metabolism. A study of the allocation of carbohydrates to a target set of metabolites during triticale acclimation to soil drought was performed. The study included a semi-dwarf cultivar ‘Woltario’ and a long-stemmed cultivar ‘Moderato’, differing in the activity of the photosynthetic apparatus under optimum growth conditions.Differences were found in the quantitative and qualitative composition of individual carbohydrates and phenolic compounds, depending on the developmental stage and water availability. Soluble carbohydrates in the semi-dwarf ‘Woltario’ cv. under soil drought were utilized for synthesis of starch, soluble phenolic compounds and an accumulation of cell wall carbohydrates. In the typical ‘Moderato’ cv., soluble carbohydrates were primarily used for the synthesis of phenolic compounds that were then incorporated into cell wall structures. Increased content of cell wall-bound phenolics in ‘Moderato’ cv. improved the cell wall tightness and reduced the rate of leaf water loss. In ‘Woltario’ cv., the increase in cell osmotic potential due to an enhanced concentration of carbohydrates and proline was insufficient to slow down the rate of leaf water loss.The mechanism of cell wall tightening in response to leaf desiccation may be the main key in the process of triticale acclimation to soil drought.

Wheat WRKY Type Transcription Factor Gene TaWRKY1 is Essential in Mediating Drought Tolerance Associated with an ABA-Dependent Pathway

WRKY-type transcription factors (TFs) are important regulators in plant growth, development and responses to diverse biotic and abiotic stresses. In this study, we characterized the function of TaWRKY1, a wheat (Triticum aestivum) WRKY family gene, in mediating plant tolerance to drought. TaWRKY1 bears a conserved WRKY motif and a C2H2 domain and targets onto the nucleus under both normal and simulated drought conditions. On exposure to simulated drought and ABA, the TaWRKY1 expression levels were significantly up-regulated. Ectopic overexpression of TaWRKY1 in tobacco conferred improved tolerance to drought; the transgenic plants exhibited more biomass, slower leaf water loss rate (WLR), more osmolyte accumulation, and higher antioxidant enzyme activities than wild type (WT) plants after drought treatments. In addition, the stomata closure rate was promoted in the transgenic plants upon exposure to drought and -exogenous ABA with respect to that in WT plants, suggesting that TaWRKY1 mediates the stomata movement and impacts the leaf water retention capacity. The transcripts of NtPYL8, an ABA receptor gene in tobacco, were shown to be induced in the TaWRKY1-overexpressing plants under drought and ABA stresses. Moreover, overexpression and knockdown of NtPYL8 modified the stomata movement characterization, leaf WLR, and phenotype of the seedlings upon exposure to the drought stress. These findings suggest that NtPYL8 acts as one of the critical players in transducing ABA signaling initiated by osmotic stress, contributing to the TaWRKY1-mediated drought tolerance via regulating stomata movement and plant water retention capacity. Our findings together reveal that TaWRKY1 plays an important role in mediating the plant tolerance to drought through modification of a set of osmotic stress-defensive processes connecting an ABA-dependent pathway. NtPYL8 and its homolog in wheat are crucial members in transducing the drought-initiated ABA signaling and are functional in modulating stomata movement.

The Functional and Regulatory Mechanisms of the Thellungiella salsuginea Ascorbate Peroxidase 6 (TsAPX6) in Response to Salinity and Water Deficit Stresses.

Soil salinization is a resource and ecological problem in the world. Thellungiella salsuginea is becoming a new model plant because it resembles its relative species, Arabidopsis thaliana, in small genome and short life cycle. It is highly tolerant to salinity and drought stresses. Ascorbate peroxidase (APX) is an enzyme that clears H2O2 in plants. The function and molecular and regulation mechanisms of APX in T. salsuginea have rarely been reported. In this study, an APX gene, TsApx6, was cloned from T. salsuginea and its responses to abiotic stresses in transgenic Arabidopsis were studied. Under high salinity treatment, the expression of TsApx6 was significantly induced. Under drought treatment, overexpression of TsApx6 increased the survival rate and reduced leaf water loss rate in Arabidopsis. Compared to the wild type plants, high salinity treatment reduced the concentrations of MDA, H2O2 and proline but elevated the activities of APX, GPX, CAT and SOD in the TsApx6-overexpressing plants. Meanwhile, germination rate, cotyledon greening, and root length were improved in the transgenic plants compared to the wild type plants under salt and water deficit conditions. Based on these findings, TsApx6 has an important function in the resistance of plants to certain abiotic stresses. The TsApx6 promoter sequence was obtained using Genome Walking technology. Bioinformatics analysis indicated that it contains some cis-acting elements related to stress response. The treatments of salt, dehydration, and ABA induced the expression of Gus gene under the regulation of the TsApx6 promoter. Mutation analysis showed that the MBS motif present in the TsApx6 promoter might be a key negative regulatory element which has an important effect on the growth and developmental process of plants.

Ethylene-insensitive mutants of Nicotiana tabacum exhibit drought stress resistance

Drought is one of the major environmental stresses that profoundly affect crop growth and yield. The gaseous hormone ethylene is believed to be critical for plant growth and drought tolerance. Based on the dark-grown seedling response to ethylene, a genetic screen for tobacco (Nicotiana tabacum) mutants on medium supplemented with ACC (1-aminocyclopropane-1-carboxylic acid), the precursor of ethylene, was performed. Among the ethylene insensitive mutants that were isolated, drought resistant mutants were subsequently obtained via screening on mannitol-containing medium. Phenotypic analyses revealed that these mutants exhibited enhanced drought resistance, having a higher percentage survival rate under conditions of severe water deficit, and better growth under mannitol osmotic stress. In the mutants, the leaf water loss rate was lowered and the leaf stomatal aperture was decreased. In addition, increases in peroxidase and superoxide dismutase activities and a higher accumulation of total soluble sugar and proline were detected in the mutant plants. The corresponding expression change of tobacco NtAP2 (APETALA2 in Nicotiana tabacum, homologous with AtAP2 from Arabidopsis thaliana) and NtERF (ethylene response factor in N. tabacum) genes was examined in the plants in response to air-drying treatments. Our study provides an applicable approach for the mutant screening of drought resistant plants, and the results suggest a crucial function of ethylene in plant drought tolerance.