Decrease In Leaf Water Content Research Articles

Arabidopsis DREB26/ERF12 and its close relatives regulate cuticular wax biosynthesis under drought stress condition.

Land plants have evolved a hydrophobic cuticle on the surface of aerial organs as an adaptation to ensure survival in terrestrial environments. Cuticle is mainly composed of lipids, namely cutin and intracuticular wax, with epicuticular wax deposited on plant surface. The composition and permeability of cuticle have a large influence on its ability to protect plants against drought stress. However, the regulatory mechanisms underlying cuticular wax biosynthesis in response to drought stress have not been fully elucidated. Here, we identified three AP2/ERF transcription factors (DREB26/ERF12, ERF13 and ERF14) involved in the regulation of water permeability of the plant surface. Transmission electron microscopy revealed thicker cuticle on the leaves of DREB26-overexpressing (DREB26OX) plants, and thinner cuticle on the leaves of transgenic plants expressing SRDX repression domain-fused DREB26 (DREB26SR). Genes involved in cuticular wax formation were upregulated in DREB26OX and downregulated in DREB26SR. The levels of very-long chain (VLC) alkanes, which are a major wax component, increased in DREB26OX leaves and decreased in DREB26SR leaves. Under dehydration stress, water loss was reduced in DREB26OX and increased in DREB26SR. The erf12/13/14 triple mutant showed delayed growth, decreased leaf water content, and reduced drought-inducible VLC alkane accumulation. Taken together, our results indicate that the DREB26/ERF12 and its closed family members, ERF13 and ERF14, play an important role in cuticular wax biosynthesis in response to drought stress. The complex transcriptional cascade involved in the regulation of cuticular wax biosynthesis under drought stress conditions is discussed.

The effect of drought‐induced leaf traits onFicusleaf palatability is species specific

AbstractDrought has a significant impact on plant–insect interactions by altering plant survival, growth, leaf quality, and defense traits. Tropical plants are particularly vulnerable to water depression because of shallow root depth. In the context of climate change, drought events are expected to increase in frequency and intensity; however, their impact on tropical ecosystems remains poorly known. Insect herbivores represent the largest feeding guild of arthropods, and they devour four to five times more plant material than vertebrates do. Understanding how drought affects plant traits and leaf palatability in a keystone and ecologically diverse plant genus, such asFicus(Moraceae), is crucial for predicting how climate change might alter tropical plant–insect interactions. We examined the impact of drought intensity and duration on the leaf nutritional quality, defensive traits, and herbivory damage by caterpillars in three tropical and one MediterraneanFicusspecies in a greenhouse. We also conducted food choice trials with generalist caterpillars to evaluate the impact of drought on herbivores. Drought intensity and duration had no direct effect on leaf palatability across theFicusspecies. However, drought indirectly affected leaf palatability via drought‐induced leaf traits in a species‐specific manner. Drought intensity and duration decreased leaf water content, resulting in decreased leaf palatability inF. benjaminaandF. lyrata. Leaf defensive traits such as flavonoid concentration were affected by drought intensity and decreased leaf palatability inF. carica. Drought influenced the leaf traits ofF. elastica, but none of them affected leaf palatability. Overall, this study establishes the link between drought and insect feeding on plants via leaf traits. The species‐specific responses to drought highlight the significance of climate‐related plant life histories in relation to climate change, underscoring the need for further investigations.

Hyperspectral imaging reveals small-scale water gradients in apple leaves due to minimal cuticle perforation by Venturia inaequalis conidiophores.

Effects of Venturia inaequalis on water relations of apple leaves were studied under controlled conditions without limitation of water supply to elucidate their impact on the non-haustorial biotrophy of this pathogen. Leaf water relations, namely leaf water content and transpiration, were spatially resolved by hyperspectral imaging and thermography; non-imaging techniques-gravimetry, a pressure chamber, and porometry-were used for calibration and validation. Reduced stomatal transpiration 3-4 d after inoculation coincided with a transient increase of water potential. Perforation of the plant cuticle by protruding conidiophores subsequently increased cuticular transpiration even before visible symptoms occurred. With sufficient water supply, cuticular transpiration remained at elevated levels for several weeks. Infections did not affect the leaf water content before scab lesions became visible. Only hyperspectral imaging was suitable to demonstrate that a decreased leaf water content was strictly limited to sites of emerging conidiophores and that cuticle porosity increased with sporulation. Microscopy confirmed marginal cuticle injury; although perforated, it tightly surrounded the base of conidiophores throughout sporulation and restricted water loss. The role of sustained redirection of water flow to the pathogen's hyphae in the subcuticular space above epidermal cells, to facilitate the acquisition and uptake of nutrients by V. inaequalis, is discussed.

Utility of L-band and X-band vegetation optical depth to examine vegetation response to soil moisture droughts in South Asia

Vegetation Water Content (VWC) holds essential information about plant photosynthetic activity, phenological changes, ability to withstand extreme events, and soil-plant-atmosphere interactions. However, there is no consensus on the extent to which Soil Moisture (SM) and atmospheric dryness (Vapor Pressure Deficit, VPD) affect VWC during droughts. In this work, we determine the causal relationships with VWC in response to VPD and SM when plants are subjected to SM droughts during the growing season. We use satellite-derived Vegetation Optical Depth (VOD), obtained from two frequencies (L- and X- bands), to represent VWC in different parts of the plant (stem, branches, and leaves). The holistic response of VOD considering VPD and SM interactions is determined using bivariate and multivariate Granger causality tests. The analysis is carried out over South Asia.The results show a statistically significant coupling between VPD and SM at semi-weekly scales over 53.20% of the study area. In these locations, we observe a dominant influence of VPD compared to SM on VODL and VODX while subjected to soil moisture droughts during the growing season. In the areas where VPD and SM are decoupled, we find both VPD and SM to influence VODL and VODX. VODL and VODX largely exhibit contrasting causal responses. We observe a surge in VODL due to water stress while subjected to soil moisture droughts under all land cover conditions. In the case of VODX, we noticed both an increase and a decrease in leaf water content while subjected to SM droughts. The former scenario is noticed predominantly under moderate to severe drought intensity conditions during which plants attempt to maintain a stable water column (through increased stomatal regulation) for their functioning as a response to SM droughts. The latter scenario is noticed in most pixels, including forests and croplands. The observed leaf water content loss in forests is due to their mild drought intensities. We also observe a stronger causal influence of VPD and SM in low LAI areas than in high LAI areas, indicating a pressing plant water stress in sparse vegetation conditions during SM droughts.

Investigating the influence of elevated temperature on nutritional and yield characteristics of mung bean (Vigna radiata L.) genotypes during seed filling in a controlled environment.

Rising temperatures impact different developmental stages of summer crops like mung bean, particularly during the crucial seed-filling stage. This study focused on two mung bean genotypes, categorized as heat-tolerant [HT] or heat-sensitive [HS]. These genotypes were grown in pots in an outdoor natural environment (average day/night temperature 36°C/24.3°C) until the onset of podding (40 days after sowing) and subsequently relocated to controlled-environment walk-in growth chambers for exposure to heat stress (42°C/30°C) or control conditions (35°C/25°C) until maturity. For all measured attributes, heat stress had a more pronounced effect on the HS genotype than on the HT genotype. Heat-stressed plants exhibited severe leaf damage, including membrane damage, reduced chlorophyll content, diminished chlorophyll fluorescence, and decreased leaf water content. Heat stress impeded the seed-filling rate and duration, decreasing starch, protein, fat, and mineral contents, with a notable decline in storage proteins. Heat stress disrupted the activities of several seed enzymes, inhibiting starch and sucrose accumulation and consequently decreasing individual seed weights and seed weight plant-1. This study revealed that heat stress during seed filling severely impaired mung bean seed yield and nutritional quality due to its impact on various stress-related traits in leaves and enzyme activities in seeds. Moreover, this research identified potential mechanisms related to heat tolerance in genotypes with contrasting heat sensitivity.

PoWRKY17 promotes drought tolerance in Paeonia ostii by modulating lignin accumulation

Drought is a detrimental environmental factor limiting sustainable agricultural development worldwide. Paeonia ostii, an oil-producing woody crop, while its endogenous mystery underlying this tolerance remains largely elusive to scholars. Herein, we reported that PoWRKY17, a WRKY transcription factor from IId subgroup, positively functioned in face of drought stress in P. ostii. PoWRKY17 expressed in significantly higher abundance when drought was applied. Silencing of PoWRKY17 substantially reduced drought resistance, with decreased leaf water content and protective enzyme activities, increased relative electric conductivity (REC), malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation. On the contrary, overexpression of PoWRKY17 endowed plants with higher drought tolerance with opposite drought-relevant physiological indices. Notably, both PoWRKY17-silenced P. ostii and PoWRKY17-overexpressing plants showed changes in lignin content under drought stress. Based on this clue, we quantified the expression of lignin biosynthetic caffeoyl-CoA O-methyltransferase (CCoAOMT) gene in PoWRKY17-silenced P. ostii and found that PoCCoAOMT expression was significantly repressed. Next, protein-gene interaction assays showed that PoWRKY17 interacted with PoCCoAOMT promoter by targeting the W-box element and activated PoCCoAOMT expression under drought stress, which has been early verified to act as a positive participant in P. ostii drought tolerance. This study broadens our understanding of WRKY-mediated lignin biosynthesis regulation in response to drought stress in plants.

A novel semi-empirical model for crop leaf area index retrieval using SAR co- and cross-polarizations

The retrieval of continuous leaf area index (LAI) in space and time from remote sensing is beneficial for cropland monitoring and management. Synthetic Aperture Radar (SAR) with the advantages of all-weather operation and fine spatial resolutions has been utilized in various agricultural applications. Although the water cloud model (WCM) has been extensively used for LAI estimation over croplands, it is modified for application to crop canopies with large gaps. The requirement of prior information on soil moisture is also a hinderance for the model application. In this study, WCM is theoretically modified to consider the correlation of active microwave propagation through the canopy in downward and upward directions. Such a modification is particularly important for sparse vegetation with large gaps between crop plants in the early stage of the growing season. A parameter with explicit physical meaning, i.e. the full-vegetation backscattering coefficient, was defined to simplify our model scheme and make the model applicable for the whole growing season. In addition, a physics-based SAR data processing scheme is developed to entangle the influences of LAI and soil moisture on SAR backscatter by taking advantage of the multiple polarizations of RADARSAT-2 (R2) SAR data. In this way, LAI was estimated using modified WCM without the prior knowledge of soil moisture. To evaluate LAI retrieved from the R2 datasets (R2 LAI), ground-based LAI measurements were made at the experimental area of SMAPVEX16-MB in Canada with twenty approximately 800 m х 800 m plots in soybeans and corn. R2 LAI was well correlated to these ground-based LAI (n = 15, R2 = 0.63, RMSE = 0.99 m2·m−2 for soybeans; n = 5, R2 = 0.66, RMSE = 1.20 m2·m−2 for corn). LAI was also retrieved from optical data acquired by Sentinel-2/MSI (S2), denoted as S2 LAI. The R2 LAI and S2 LAI are well correlated and achieved coefficients of determination (R2) of 0.76 and 0.71 and root mean square errors (RMSE) of 1.1 and 1.4 m2·m−2 for soybeans and corn, respectively. The seasonal variations of R2 LAI and S2 LAI are generally similar except at the end of the growing season when S2 LAI is considerably larger than R2 LAI. S2 LAI followed the trend of the reduction in leaf chlorophyll content, while R2 LAI reduced only slightly due to the decrease in leaf water content near the end the growing season. R2 LAI represents the total standing leaf area useful for surface energy balance estimation, while S2 LAI responds to green leaf area useful for crop productivity modeling.

Prolonged low temperature exposure de-sensitises ABA-induced stomatal closure in soybean, involving an ethylene-dependent process.

Chilling can decrease stomatal sensitivity to abscisic acid (ABA) in some legumes, although hormonal mechanisms involved are unclear. After evaluating leaf gas exchange of 16 European soybean genotypes at 14°C, 6 genotypes representing the range of response were selected. Further experiments combined low (L, 14°C) and high (H, 24°C) temperature exposure from sowing until the unifoliate leaf was visible and L or H temperature until full leaf expansion, to impose four temperature treatments: LL, LH, HL, and HH. Prolonged chilling (LL) substantially decreased leaf water content but increased leaf ethylene evolution and foliar concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, indole-3-acetic acid, ABA and jasmonic acid. Across genotypes, photosynthesis linearly increased with stomatal conductance (Gs), with photosynthesis of HH plants threefold higher than LL plants at the same Gs. In all treatments except LL, Gs declined with foliar ABA accumulation. Foliar ABA sprays substantially decreased Gs of HH plants, but did not significantly affect LL plants. Thus low temperature compromised stomatal sensitivity to endogenous and exogenous ABA. Applying the ethylene antagonist 1 methyl-cyclopropene partially reverted excessive stomatal opening of LL plants. Thus, chilling-induced ethylene accumulation may mediate stomatal insensitivity to ABA, offering chemical opportunities for improving seedling survival in cold environments.

Transgenic Chrysanthemum indicum overexpressing cin-miR396a exhibits altered plant development and reduced salt and drought tolerance

The conserved microRNA396 (miR396) is involved in growth, development, and abiotic stress responses in a variety of plants by regulating target genes. Here, we obtained transgenic Chrysanthemum indicum (C. indicum) overexpressing the cin-miR396a gene. The transgenic plants (TGs) had longer internodes and fewer epidermal hairs in contrast with the wild-type (WT) control. cin-miR396a overexpression in C. indicum reduced salt tolerance and drought tolerance. After salt and drought stress compared with WT plants, the transgenic C. indicum exhibited a relative decrease in leaf water content, and the leaf free proline content, also exhibited a relative increase, in the leaf conductivity and leaf Malondialdehyde content, while the total chlorophyll content did not differ significantly from WT, and the Na+/K+ ratio in the roots of transgenic C. indicum increased after salt stress. We also identified two target genes of cin-miR396a, CiGRF1 and CiGRF5, whose expression was induced by salt and drought treatments and suppressed in transgenic C. indicum. Taken together, our results reveal a unique role for the regulatory module of miR396a-GRFs in C. indicum development and response to abiotic stresses. cin-miR396a plays a negative regulatory role in C. indicum in response to salt and drought stresses.

Accumulation of Silicon and Changes in Water Balance under Drought Stress in Brassica napus var. napus L.

The aim of this study was to investigate the accumulation of silicon in oilseed rape and to characterize the changes in chosen water balance parameters in response to drought. The following parameters were estimated: water content, osmotic and water potential, evapotranspiration, stomatal conductance and abscisic acid level under optimal and drought conditions. It was shown that oilseed rape plants accumulate silicon after its supplementation to the soil, both in the case of silicon alone and silicon together with iron. It was revealed that silicon (without iron) helps maintain constant water content under optimal conditions. While no silicon influence on osmotic regulation was observed, a transpiration decrease was detected under optimal conditions after silicon application. Under drought, a reduction in stomatal conductance was observed, but it was similar for all plants. The decrease in leaf water content under drought was accompanied by a significant increase in abscisic acid content in leaves of control plants and those treated with silicon together with iron. To sum up, under certain conditions, silicon is accumulated even in non-accumulator species, such as oilseed rape, and presumably improves water uptake under drought stress.

Phenylurea-type Cytokinin ameliorates the performance of young pea plants under salt stress

Cytokinins are known to enhance stress tolerance in plants. The present study aimed to assess the possible protective effect of exogenous phenylurea-type cytokinin (4PU-30) on alleviating salt (NaCl) stress. Young pea (Pisum sativum L.) plants were sprayed with cytokinin 4PU-30 and were subsequently subjected to NaCl treatment. The effect of 4PU-30 on cell membrane stability was assessed based on electrolyte leakage from leaves of control and NaCl stressed plants. A previously established model system employing the kinetics of ion leakage served to evaluate the effect of the 4PU-30 application on plants response to salinity. Salt treatment caused a moderate decrease in leaf water content. Accumulation of proline, malondialdehyde (MDA), and hydrogen peroxide (H2O2) in the leaves of NaCl treated plants indicated the development of oxidative stress, which was significantly alleviated by pretreatment with phenylurea-type cytokinin 4PU-30. Foliar application of 4PU-30 reduced the damaging effect of NaCl, as evidenced by decreased electrolyte leakage. Distinct roles of cell walls and plasmalemma in the processes of ion efflux due to salt stress are discussed.

The effect of drought on physiological responses of forage plants to salt stresses depends on occurring time

Drought and salinity are two common abiotic stresses that restrain plant growth and often co-occur, either simultaneously or sequentially. However, the effect of drought on physiological responses of plants to salinity remains unclear. Accordingly, we selected three forage species that differ in drought and salinity tolerance: ryegrass (Lolium perenne L.), alfalfa (Medicago sativa L.) and switchgrass (Panicum virgatum L.). Independent and combined (sequential and simultaneous pattern) drought and salinity were carried out in a pot experiment. Salinity severely injured the plants through decreasing leaf water content and increasing Na+ and Cl− concentrations. Compared to the individual salinity treatment, the sequential drought and salinity treatment remarkably enhanced the leaf water status and decreased toxic ion uptake, thereby decreasing levels of reactive oxygen species (ROS), malondialdehyde, and membrane leakage. In contrast, the oxidative damage that resulted from the simultaneous stress treatment was more pronounced than that produced by the independent salinity treatment, which can be attributed to decreased water content, increased toxic ion intake, or/and reduced antioxidant activity. Our results suggested that the physiological responses to combined drought and salinity remarkably depends on the temporal pattern of those stresses.

Burning-induced electrical signals influence broadband reflectance indices and water index in pea leaves

ABSTRACTElectrical signals (ESs) can be induced by local action of stressors in plants; they influence numerous physiological processes (photosynthesis, transpiration, respiration, genes expression, synthesis of phytohormones, etc.) and, thereby, induce a systemic adaptation response. Development of optical methods of a remote sensing of this response can be important for agricultural and ecological monitoring. Preliminarily, we showed (Sukhova et al., Plant Sign Behav 2019; 14:e1610301) that burning-induced ESs induced changes in leaf reflectance at broad spectral bands (400–500, 500–600, 600–700, and 700–800 nm). The aims of the present work were (i) investigation of ESs influence on difference reflectance indices (RIs) calculated on the basis of these broad spectral bands and (ii) analysis of connection of the indices with water content in plants. Pea seedlings were investigated. ESs were induced by burning of the first mature leaf; ESs had high amplitudes in the second leaf and had low amplitudes in the fourth leaf. It was shown that ESs induced significant changes in RIs, which were calculated on basis of intensities of the reflected light at (i) 400–500 and 600–700 nm, (ii) 500–600 and 700–800 nm, and (iii) 600–700 and 700–800 nm. The effect was strong in the second leaf and weak in the fourth leaf; that is, the response was dependent on the magnitude of ESs. ESs-induced changes in RI were strongly connected with ESs-induced decrease of leaf water content which was estimated on basis of decrease of water index. Thus, broadband RIs can be used for revealing the ESs-induced systemic stress response in plants.

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.

Morpho-physiological responses of tall wheatgrass populations to different levels of water stress.

Tall wheatgrass [Elymus elongatus subsp. ponticus (Podp.) Melderis] is a perennial forage grass cultivated in dry, saline or alkaline environments. The morpho-physiological characteristics of four populations of tall wheatgrass from different climatic-edaphic origins were evaluated under three conditions of water stress (100%-50%-30% of field capacity). The trial was analyzed with three replicates and two-factor ANOVA in pots within the greenhouse during 35 days. Only dry matter and tiller number showed interaction between populations and water conditions. The most relevant changes in morpho-physiological parameters under strong water stress were reduced dry matter production (48–32% differing among populations), smaller leaf and tiller size (46% and 28%), together with higher water use efficiency (74%), and increased proline and protein contents (144% and 71%), smaller tiller number (30–11% differing among populations) and a slight decrease in leaf water content (3%). The populations differed in growth strategies and morpho-physiological mechanisms to survive water stress, which could be related to their habitat background. The study shows the stability in dry matter production under all levels of water stress, which can be related to the higher tiller number. Due to this plasticity, tall wheatgrass should be studied as a species with great potential to adapt to drought stress.

Greenhouse vapour pressure deficit and lighting conditions during growth can influence postharvest quality through the functioning of stomata

There is a tendency in horticulture to grow plants in greenhouses with high humidity and prolonged light periods, especially in winter. Although plants grow well in greenhouses with high relative humidity (RH) (low vapour pressure deficit; VPD), the plants produced under such greenhouse climates have limited control over water loss after harvest, leading to uncontrolled transpiration and decreased water content in the postharvest stage. This results in shortened vase-life of cut flowers and decreased quality of leafy vegetables. When plants had been produced in greenhouses with moderate humidity and natural day length, their stomata close when they are exposed to stomata closure-promoting environments (low RH, desiccation and darkness), as usually happens during the postharvest stage. However, in greenhouses with low VPD conditions and long photoperiods, stomata will not fully close during the postharvest stage; even decreased leaf water content will not result in full stomatal closure (stomatal malfunctioning) in products coming from those greenhouses. In this paper, greenhouse climate factors during the growth of plants that induce stomatal malfunctioning in the postharvest stage will be characterised. Approaches will be discussed to improve stomatal functionality under such greenhouse conditions in order to increase vase- and shelf-lives of products.

Comparative physiological responses and adaptive strategies of apple Malus halliana to salt, alkali and saline-alkali stress

Malus halliana Koehne (M. halliana) is a native rootstocks to the saline-alkali soil of Northwest China which shows a higher saline-alkali tolerance than other apple rootstocks. However, there are few studies of saline-alkali resistance on M. halliana. This study was aimed to elucidated the physiological adaptive mechanisms of M. halliana involved in the responce to three different stress factors. The salt stress (SS), alkali stress (AS) and saline–alkali stress (MAS) were applied to study the different responses of ion, photosynthesis, Chl fluorescence, antioxidant enzymes and osmolytes for 40 days. The results showed that M. halliana accumulated more Na+ in roots and less K+ in leaves under AS compared to the SS and MAS treatments. M. halliana plants adapted to three stresses by decreasing leaf water content (WC), stomatal conductance (Gs) and intercellular CO2 concentration (Ci), increasing water use efficiency (WUE) and accumulating osmolytes. However, the respond mechanisms of M. halliana to SS, AS and MAS were different. Under SS, M. halliana plants adapted to stress by improving the activity of superoxide dismutase (SOD) and peroxidase (POD) and starting thermal dissipation protection mechanism. Under AS, plants mianly accumulated the organic acids (OA) to adjust osmotic balance and triggered xanthophyll cycle to dissipate excess energy. Under MAS, plants kept the dynamic balance of photosynthetic system between injury and repair by starting heat dissipation mechanism and xanthophyll cycle. And it also mianly accumulated osmolytes to maintain osmotic regulation and improved the activity of antioxidant enzyme to avoid oxidative damage. In addition, the analysis of principal component found that Gs, Ci, WC, Chl a + b (Chlorophyll), Fm (maximum fluorescence), Fv/Fm (maximal photochemical efficiency), ETR(photosynthetic electron transport rate), ΦPSII (actual photochemical efficiency) and qP (photochemical quenching coefficient) were major influencing factors to the decreasing of Pn (net photosynthetic rate). In summary, the inhibitory effects of growth and photosynthesis on M. halliana under three stresses were AS > MAS > SS. Under MAS, the salt and alkail had a certain synergistic effect.

Changes in Leaf and Shoot Water Statutes of Grapevines in Response to Contrasting Water Availability and Glycine Betaine Pulverization

Drought is one of the most widespread stress factors adversely affecting plant growth, crop yield and quality. In Subtropical region, on the face of global warming, temperature extremes aggravate the negative effects of drought. Increased resistance to stress has been achieved in several plants by exogenous application of various organic osmoprotectants. In this study, the role of glycine betaine (GB) as exogenous application, is aimed to investigate for increasing grapevine stress tolerance to drought. The grapevines of Alphonse Lavalléeʼ cultivar, grafted on the rootstock 41 B, were subjected to four different applications; (1) full irrigation (FI) as control (irrigation at field capacity level), (2) deficit irrigation (DI, 50% of FI), (3) DI plus 5000 ppm GB pulverization, and (4) DI plus 10000 ppm GB pulverization in a pot experiment under glasshouse condition. Leaf fresh weight of vines subjected to DI was 31.8% lower than those of FI vines. GB appeared to exert an influence on leaf water statute, slightly alleviating the leaf water loss resulting from water shortage. GB treatments, regardless of the concentration, slightly increased the fresh weight of the leaves (22.2% lower than FI). Investigations on leaf turgid weight and dry weight were also similar to those of fresh weight in that the highest and the lowest values were determined in FI and DI applications, respectively. Reduction in shoot water content in response to water deficit was closely related to the decrease in leaf water content.

Polymorphism of microsatellite markers in barley varieties contrasting in response to drought stress

Drought is one of the most serious abiotic stresses limiting plant growth and crop productivity worldwide. The long arm of the barley chromosome 4H is often implicated in adaptation to drought. Therefore, the aim of the present study was to explore the polymorphism of microsatellite markers localized mostly on chromosome 4H in eight barley varieties (Hordeum vulgare L.) representing the wide range of drought tolerance. The differences in physiological responses related to drought stress classified these genotypes in two groups based on the Euclidean distances. The susceptible varieties are gathered in the same cluster recording an average Euclidean distance of 27.2, and an average dissimilarity of approximately 52.4 regarding the drought-tolerant group. Tolerance to drought stress of the Tunisian and Jordanian barley cultivars was associated with lower changing ratios of malondialdehyde contents, smaller decrease in leaf water content and significant increase in proline concentration compared to other analyzed genotypes. In simple sequence repeat (SSR) analyses, from a total of 17 analyzed SSR primers, 12 microsatellites showed clear patterns with high level of polymorphism. Among the 12 polymorphic SSR primers, four were found to be polymorphic across drought susceptible and drought-tolerant cultivars (Bmag808, EBMAC624, WMS6 and BMAC0577). High level of diversity was observed in the chosen genotypes through analyzing both physiological traits and SSR markers. A significant correlation was observed between the distance matrices based on SSR markers and physiological data, as determined by the Pearson’s correlation coefficient (r = 0.63; Mantel test P < 0.05).

Effects and mechanism of acid rain on plant chloroplast ATP synthase.

Acid rain can directly or indirectly affect plant physiological functions, especially photosynthesis. The enzyme ATP synthase is the key in photosynthetic energy conversion, and thus, it affects plant photosynthesis. To clarify the mechanism by which acid rain affects photosynthesis, we studied the effects of acid rain on plant growth, photosynthesis, chloroplast ATP synthase activity and gene expression, chloroplast ultrastructure, intracellular H(+) level, and water content of rice seedlings. Acid rain at pH 4.5 remained the chloroplast structure unchanged but increased the expression of six chloroplast ATP synthase subunits, promoted chloroplast ATP synthase activity, and increased photosynthesis and plant growth. Acid rain at pH 4.0 or less decreased leaf water content, destroyed chloroplast structure, inhibited the expression of six chloroplast ATP synthase subunits, decreased chloroplast ATP synthase activity, and reduced photosynthesis and plant growth. In conclusion, acid rain affected the chloroplast ultrastructure, chloroplast ATPase transcription and activity, and P n by changing the acidity in the cells, and thus influencing the plant growth and development. Finally, the effects of simulated acid rain on the test indices were found to be dose-dependent.