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SUMMARY: Polyamines are involved in several plant physiological processes. In Arabidopsis thaliana, five FAD‐dependent polyamine oxidases (AtPAO1 to AtPAO5) contribute to polyamine homeostasis. AtPAO5 catalyzes the back‐conversion of thermospermine (T‐Spm) to spermidine and plays a role in plant development, xylem differentiation, and abiotic stress tolerance. In the present study, to verify whether T‐Spm metabolism can be exploited as a new route to improve stress tolerance in crops and to investigate the underlying mechanisms, tomato (Solanum lycopersicum) AtPAO5 homologs were identified (SlPAO2, SlPAO3, and SlPAO4) and CRISPR/Cas9‐mediated loss‐of‐function slpao3 mutants were obtained. Morphological, molecular, and physiological analyses showed that slpao3 mutants display increased T‐Spm levels and exhibit changes in growth parameters, number and size of xylem elements, and expression levels of auxin‐ and gibberellin‐related genes compared to wild‐type plants. The slpao3 mutants are also characterized by improved tolerance to drought stress, which can be attributed to a diminished xylem hydraulic conductivity that limits water loss, as well as to a reduced vulnerability to embolism. Altogether, this study evidences conservation, though with some significant variations, of the T‐Spm‐mediated regulatory mechanisms controlling plant growth and differentiation across different plant species and highlights the T‐Spm role in improving stress tolerance while not constraining growth. [ABSTRACT FROM AUTHOR]

Spectral indices can be used as fast and non‐destructive indicators of plant water status or stress. It is the objective of the present study to evaluate the feasibility of using several spectral indices including water index (WI) and normalized spectral water indices 1–5 (NWI 1–5) to estimate water status in olive trees in arid regions in Iran. The experimental treatments involved two olive cultivars (Koroneiki and T2) and four irrigation regimes (irrigated with 100%, 85%, 70%, and 55% estimated crop evapotranspiration [ETc]). The results obtained showed that olive trees subjected to the different irrigation regimes of 85%, 70%, and 55% ETc experienced soil water content (SWC) deficits by 4.5%, 12%, and 20.5% that of the control, respectively. Significant differences were observed among the treatments with respect to measured relative water content (RWC), SWC, and the spectral indices of WI and NWI 1–5. The normalized spectral indices combining NIR and NIR wavelengths were found more effective in tracking changes in RWC and SWC than those that combine NIR and VIS or VIS and VIS wavelengths, respectively. Spectral indices were closely and significantly associated with RWC (.63**

Desiccation-tolerant vascular (DT) plants are predominant occupants of rock outcrops in tropical regions. Though rock outcrops are common landscapes in the Western Ghats (WG), a biodiversity hotspot in India, knowledge of DT plants in the region is poor. This study provides an overview of Indian DT vascular plants, emphasizing the WG, and includes an inventory of species with their habitat preferences. Outcrop species were scrutinized for their DT properties by seasonal field observations, followed by relative water content estimation protocols. The inventory revealed 62 DT species, many more than the earlier known nine species. Nine genera of DT plants are reported as new also in a global perspective, and Tripogon capillatus represent the first record of an epiphytic DT angiosperm. We also provide the first field observation-based proof of DT properties of the gesneriad Corallodiscus lanuginosus. Of the 62 species, 16 are Indian endemic, and 12 are exclusive to Western Ghat outcrops, highlighting WG's importance as a global DT hotspot. In addition to rock outcrops, partially shaded sites in forests are crucial habitats for DT species. This pioneering inventory addresses India's need for more knowledge on DT plants and opens new research avenues. [ABSTRACT FROM AUTHOR]

A barley drought tolerance Quantitatif Trait Locus (QTL) on chromosome 2 was transferred from tolerant cultivar 'Tadmor' to susceptible 'Baronesse' and 'Aydanhanım'. Effects of this QTL on drought tolerance and other traits were studied using near‐isogenic lines under controlled environments and field trials for two years. This QTL resulted in 5.0% and 9.1% improvement in leaf relative water content of 'Baronesse' and 'Aydanhanım' cultivars, respectively, under controlled environments. The QTL accelerated heading and maturity by 2.5 days in 'Baronesse' and by 5–6 days in 'Aydanhanım'. It was associated with shorter stature and more ears. This QTL region increased grain yields by 1.1 and 0.6 t/ha in 'Baronesse' and 'Aydanhanım', respectively, mainly by increasing the number of tillers. There were previous reports related to yield promoting effects of this region harbouring flowering locus eps2 (barley HvCEN gene). However, sequencing of 1025 bp fragment encompassing HvCEN coding region revealed that our parents and near‐isogenic lines had no Single Nucleotide Polymorphism (SNP) variation, ruling out direct involvement of eps2. These findings pointed to the possible effect of another flowering locus in the QTL region. [ABSTRACT FROM AUTHOR]

Summary: Xylem hydraulic failure (HF) has been identified as a ubiquitous factor in triggering drought‐induced tree mortality through the damage induced by the progressive dehydration of plant living cells. However, fundamental evidence of the mechanistic link connecting xylem HF to cell death has not been identified yet. The main aim of this study was to evaluate, at the leaf level, the relationship between loss of hydraulic function due to cavitation and cell death under drought conditions and discern how this relationship varied across species with contrasting resistances to cavitation.Drought was induced by withholding water from potted seedlings, and their leaves were sampled to measure their relative water content (RWC) and cell mortality. Vulnerability curves to cavitation at the leaf level were constructed for each species.An increment in cavitation events occurrence precedes the onset of cell mortality. A variation in cells tolerance to dehydration was observed along with the resistance to cavitation.Overall, our results indicate that the onset of cellular mortality occurs at lower RWC than the one for cavitation indicating the role of cavitation in triggering cellular death. They also evidenced a critical RWC for cellular death varying across species with different cavitation resistance. [ABSTRACT FROM AUTHOR]

Microwave radiometry can be used to measure vegetation water content through vegetation optical depth (VOD). VOD can vary due to changes in water stress alone, but also scales with aboveground biomass. Several studies have therefore interpreted VOD temporal anomalies as linearly proportional to biomass anomalies, neglecting the influence of water stress. Here, we explicitly test this assumption using a new annual‐resolution data set of biomass derived from optical, radar, and lidar remote sensing. Both L‐band and X‐band VOD datasets are tested. Although VOD and biomass variations are highly correlated in space, their temporal anomalies are almost uncorrelated. At regional scale, it is as common for VOD anomalies to be more correlated to root‐zone soil moisture anomalies (a proxy for water stress) than to biomass anomalies as for the opposite to occur. Care should therefore be taken when deriving biomass anomalies from VOD, especially in the absence of any large‐scale biomass disturbances. Plain Language Summary: Satellite measurements known as vegetation optical depth (VOD) measure how much water is in plants. Because plants with more mass can hold more water, changes in VOD are used to determine biomass changes, ignoring the fact that changes in how dry the plants are also affect VOD. We use an alternative data set for biomass to test this approach. At a given location, VOD and biomass do not vary in the same pattern from year to year and for many types of plants, VOD seems to follow soil moisture (which should co‐vary with the fraction of water in plants) better than it follows biomass itself. These results help clarify when VOD can and can't provide information about biomass. Key Points: We test the common literature assumption that biomass interannual variability (IAV) follows vegetation optical depth (VOD) IAVVOD‐biomass relationship is driven almost entirely by spatial correlation, rather than temporal similarityRegional‐scale VOD IAV is often more sensitive to soil moisture than biomass, due to influence of plant water stress on VOD [ABSTRACT FROM AUTHOR]

In nature, plants may suffer rapid dehydration (RD), which causes significant loss of the annual global chickpea production. Thus, ascertaining more knowledge concerning the RD‐tolerance mechanisms in chickpea is crucial for developing high drought‐tolerant varieties to assure sustainable chickpea production under sudden water deficit. Here, we focused on genotype‐driven variation in leaf relative water content (RWC) and associated differences in RD‐responsive physiological and biochemical attributes in roots and leaves of two chickpea varieties, FLIP00‐21C and FLIP02‐89C, subjected to well‐watered and RD conditions. FLIP00‐21C showed higher RD‐tolerance than FLIP02‐89C, evident by its higher leaf RWC during RD. Consistently, FLIP00‐21C exhibited lower membrane injury due to lower hydrogen peroxide (H2O2) accumulation than FLIP02‐89C during RD, indicating reduced RD‐induced oxidative damage. Under RD conditions, total phenolics in roots and flavonoids in roots and leaves increased more in FLIP02‐89C compared to FLIP00‐21C; however, the increased activities of superoxide dismutase and H2O2‐scavenging enzymes were more properly coordinated in FLIP00‐21C than in FLIP02‐89C, which might contribute to more efficient antioxidant defense in FLIP00‐21C than in FLIP02‐89C. The higher leaf RWC of FLIP00‐21C versus FLIP02‐89C under RD might be associated with greater increases in the levels of the osmo‐regulators proline and total free amino acids (TFAAs) in FLIP00‐21C than in FLIP02‐89C. Collectively, the higher RD‐tolerance of FLIP00‐21C is mainly associated with the maintenance of higher RWC, stronger antioxidant defense, and greater accumulation of proline and TFAAs. These traits could be useful for evaluating the drought‐tolerance of chickpea varieties and further marker‐assisted breeding approaches for improvement of chickpea productivity. [ABSTRACT FROM AUTHOR]

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Water availability directly influences interactions and competition between weeds and crops. This article is based on the idea that relative water content (RWC) indicates the water uptake within plants and that it is possible to explain the water relationships between plants that are growing together. A field experiment carried out for 3 years (2013–2014, 2014–2015 and 2015–2016) compared the short‐term effects of years and tillage systems on wheat grain yield, weed density, wheat‐RWC, weed‐RWC and soil water content (SWC), at tillering and flowering stages in a winter wheat monoculture system. The three tillage treatments were conventional tillage (CT), minimum tillage (MT) and no‐tillage (NT). Wheat grain yield was low all years of study, because of low interannual rainfall, and we did not observe differences between tillage systems. Weed density was also affected by year and not by tillage systems. Lowest winter rainfall (73.4 mm from Nov to Feb) in the last year of the study (2015–2016), decreased the weed density in all tillage systems. Despite the rainfall variability over the 3 years of study, the NT system presented higher weed density (73 plants/m2) than MT and CT systems (39.83 and 46.33 plants/m2). We also observed a higher number of weed species for the NT system, facilitated by a high soil water storage in this system. The wheat‐RWC, at tillering stage, varied with years and tillage systems; we found that high winter rainfall (2013–2014) led to higher values in CT (64.5%) compared with MT (52.9%) and NT plots (52.9%). Weed‐RWC values did not vary and SWC was greater in NT than in CT and MT. At flowering stage, the year (2015–2016) with highest spring rainfall favoured higher wheat‐RWC in NT (56.9%) compared with CT (48.3%). However, the lowest spring rainfall coincided with the lowest weed‐RWC, (18% in NT plots) and SWC was always higher in NT soils. The results showed that climatic conditions affected the water competence dynamics between weeds and wheat in different ways. Seemingly, weeds can tolerate a lack of water availability until crop tillering stage independently of tillage system; however, the competition for water was not a problem as crops overcame the high weed density by flowering stage. [ABSTRACT FROM AUTHOR]

The tonoplast sucrose transporter PtaSUT4 is well expressed in leaves of Populus tremula × Populus alba (INRA 717‐IB4), and its inhibition by RNA‐interference (RNAi) alters leaf sucrose homeostasis. Whether sucrose partitioning between the vacuole and the cytosol is modulated by PtaSUT4 for specific physiological outcomes in Populus remains unexplored. In this study, partial defoliation was used to elicit compensatory increases in photosynthesis and transpiration by the remaining leaves in greenhouse‐grown poplar. Water uptake, leaf gas exchange properties, growth and nonstructural carbohydrate abundance in source and sink organs were then compared between wild‐type and SUT4‐RNAi lines. Partial defoliation increased maximum photosynthesis rates similarly in all lines. There was no indication that source leaf sugar levels changed differently between wild‐type and RNAi plants following partial defoliation. Sink levels of hexose (glucose and fructose) and starch decreased similarly in all lines. Interestingly, plant water uptake after partial defoliation was not as well sustained in RNAi as in wild‐type plants. While the compensatory increase in photosynthesis was similar between genotypes, leaf transpiration increased less robustly in RNAi than wild‐type plants. SUT4‐RNAi and wild‐type source leaves differed constitutively in their bulk modulus of elasticity, a measure of leaf turgor, and storage water capacitance. The data demonstrate that reduced sucrose partitioning due to PtaSUT4‐RNAi altered turgor control and compensatory transpiration capacity more strikingly than photosynthesis and sugar export. The results are consistent with the interpretation that SUT4 may control vacuolar turgor independently of sink carbon provisioning. [ABSTRACT FROM AUTHOR]

Summary: Catastrophic failure of the water transport pathway in trees is a principal mechanism of mortality during extreme drought. To be able to predict the probability of mortality at an individual and landscape scale we need knowledge of the time for plants to reach critical levels of hydraulic failure.We grew plants of eight species of Eucalyptus originating from contrasting climates before allowing a subset to dehydrate. We tested whether a trait‐based model of time to plant desiccation tcrit, from stomatal closure gs90 to a critical level of hydraulic dysfunction Ψcrit is consistent with observed dry‐down times.Plant desiccation time varied among species, ranging from 96.2 to 332 h at a vapour‐pressure deficit of 1 kPa, and was highly predictable using the tcrit model in conjunction with a leaf shedding function. Plant desiccation time was longest in species with high cavitation resistance, strong vulnerability segmentation, wide stomatal‐hydraulic safety, and a high ratio of total plant water content to leaf area.Knowledge of tcrit in combination with water‐use traits that influence stomatal closure could significantly increase our ability to predict the timing of drought‐induced mortality at tree and forest scales. [ABSTRACT FROM AUTHOR]

Summary: Although primarily valued for their suitability for oceanographic applications and soil moisture estimation, microwave remote sensing observations are also sensitive to plant water content (Mw). Since Mw depends on both plant water status and biomass, these observations have the potential to be useful for a range of plant drought response studies. In this paper, we introduce the principles behind microwave remote sensing observations to illustrate how they are sensitive to plant water content and discuss the relationship between landscape‐scale Mw and common stand‐scale metrics, including plant‐scale relative water content, live fuel moisture content and leaf water potential. Lastly, we discuss how various sensor types can be leveraged for specific applications depending on the spatio‐temporal resolution needed. [ABSTRACT FROM AUTHOR]

Summary: Drought‐induced tree mortality has major impacts on ecosystem carbon and water cycles, and is expected to increase in forests across the globe with climate change. A large body of research in the past decade has advanced our understanding of plant water and carbon relations under drought. However, despite intense research, we still lack generalizable, cross‐scale indicators of mortality risk. In this Viewpoint, we propose that a more explicit consideration of water pools could improve our ability to monitor and anticipate mortality risk. Specifically, we focus on the relative water content (RWC), a classic metric in plant water relations, as a potential indicator of mortality risk that is physiologically relevant and integrates different aspects related to hydraulics, stomatal responses and carbon economy under drought. Measures of plant water content are likely to have a strong mechanistic link with mortality and to be integrative, threshold‐prone and relatively easy to measure and monitor at large spatial scales, and may complement current mortality metrics based on water potential, loss of hydraulic conductivity and nonstructural carbohydrates. We discuss some of the potential advantages and limitations of these metrics to improve our capacity to monitor and predict drought‐induced tree mortality. [ABSTRACT FROM AUTHOR]

The present study was designed to check the role of silver nanoparticles (AgNPs) on physiological, biochemical parameters and antioxidants of wheat (Triticum aestivum L.) under heat stress. Plant extract of Moringa oleifera was used for AgNPs synthesis followed by characterization through UV–Vis spectroscopy, SEM, XRD and Zeta analyser. Heat stress was applied in range of 35–40°C for 3 hrs/ day for 3 days to wheat plants at trifoliate stage. Heat stress decreased the RWC (13.2%), MSI (16.3%), chl a (5.2%), chl b (4.1%) and TCCs (9.9%). Wheat plants treated with AgNPs showed significant increase in RWC (12.2%), MSI (26.5%), chl a (10%), chl b (16.4%), TCCs (19%), TPC (2.4%), TFC (2.5%), TASC (2.5%), SOD (1.3%), POX (1.5%), CAT (1.8%), APX (1.2%) and GPX (1.4%), under heat stress. Lower concentration of AgNPs (50 mg/l) decreased the sugar (5.8%) and proline contents (4%), while increase was observed in higher AgNPs concentrations. Overall, AgNPs treatment enhanced thermo‐tolerance in wheat plants, but the mechanism of AgNPs action needs further investigation at genome and proteome level in wheat plants under heat stress. [ABSTRACT FROM AUTHOR]

We previously reported an alfalfa half-sib family, HS-B, with improved salt tolerance, compared to parental plants, P-B. In this study, we conducted additional experiments to address potential physiological mechanisms that may contribute to salt tolerance in HS-B. Vegetatively propagated HS-B and P-B plants were treated with a nutrient solution (control) or a nutrient solution containing NaCl ( EC = 12 dS/m). Shoots and roots were harvested at various time points after treatment for quantification of proline, soluble sugar, and H2O2 using spectrophotometers. Subcellular localization and quantification of Na in roots were conducted using a Na+-specific dye under a confocal microscope. HS-B produced 86 and 89% greater shoot and root dry biomass, respectively, compared to parental plants, P-B, under salinity in the greenhouse. Under saline conditions the HS-B shoots accumulated 115% and roots 55% more soluble sugars than P-B counterparts. The non-saline HS-B shoots, however, showed 72% less soluble sugars than the non-saline P-B plants. Under saline conditions HS-B accumulated 39% less proline in shoots, while roots accumulated 56% more proline, compared to their P-B parents. HS-B plants also showed a greater reduction of stomatal conductance under mild saline stress. HS-B shoots and roots contained 3-4 times less reactive oxygen species (H2O2) after salt treatment compared to P-B plants. Sodium localization and distribution analysis using Na+-specific dye revealed HS-B plants accumulated 88% and 48% less Na+ in stele and xylem vessels compared to P-B. The study provides insights into the potential mechanisms that may contribute to salt tolerance in HS-B: maintaining RWC by accumulating soluble sugars while reducing transpiration, maintaining healthy status by reducing oxidative stresses, and preventing salt toxicity by reducing accumulation of Na+ inside root cells and xylem. [ABSTRACT FROM AUTHOR]

BACKGROUND Until now, the majority of methods employed to assess grapevine water status have been destructive, time-intensive, costly and provide information of a limited number of samples, thus the ability of revealing within-field water status variability is reduced. The goal of this work was to evaluate the capability of non-invasive, portable near infrared ( NIR) spectroscopy acquired in the field, to assess the grapevine water status in diverse varieties, grown under different environmental conditions, in a fast and reliable way. The research was conducted 2 weeks before harvest in 2012, in two commercial vineyards, planted with eight different varieties. Spectral measurements were acquired in the field on the adaxial and abaxial sides of 160 individual leaves (20 leaves per variety) using a commercially available handheld spectrophotometer (1600-2400 nm). RESULTS Principal component analysis ( PCA) and modified partial least squares ( MPLS) were used to interpret the spectra and to develop reliable prediction models for stem water potential ( Ψs) (cross-validation correlation coefficient ( rcv) ranged from 0.77 to 0.93, and standard error of cross validation ( SECV) ranged from 0.10 to 0.23), and leaf relative water content ( RWC) ( rcv ranged from 0.66 to 0.81, and SECV between 1.93 and 3.20). The performance differences between models built from abaxial and adaxial-acquired spectra is also discussed. CONCLUSIONS The capability of non-invasive NIR spectroscopy to reliably assess the grapevine water status under field conditions was proved. This technique can be a suitable and promising tool to appraise within-field variability of plant water status, helpful to define optimised irrigation strategies in the wine industry. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Two old (Huangsedadou and Longxixiaohuangpi (LX)) and two new (Jindou 19 (JD) and Zhonghuang 30 (ZH)) soya bean (Glycine max (L.) Merr.) cultivars were used to investigate the influence of soil drying on the abscisic acid (ABA) accumulation in leaves, stomatal conductance (gs), leaf water relations, osmotic adjustment (OA), leaf desiccation tolerance, yield and yield components. The greater ABA accumulation was induced by soil drying, which also inducing gs decreased at higher soil water contents (SWC) and leaf relative water content (RWC) significantly decreased at lower SWC in the new soya bean cultivars than in the old soya bean cultivars. The soil water threshold between the value at which stomata began to close and the RWC began to decrease was significantly broader in the new cultivars than in the old cultivars. The new cultivars had significantly higher OA and lower lethal leaf water potential than old cultivars when the soil dried. The old cultivars had greater biomass, but lower grain yield than the new cultivars in well-watered, moderate stress and severe stress conditions. Thus with soil drying, the new soya bean cultivars demonstrated greater adaptation to drought by inducing greater ABA accumulation, stomatal closure at higher SWC, enhanced OA and better water relations, associated with increased leaf desiccation tolerance, greater water use efficiency and higher yield. [ABSTRACT FROM AUTHOR]

The extent of an external water layer around moss tissue influences CO2 assimilation. Experiments on the desiccation-tolerant moss Syntrichia ruralis assessed the real-time dependence of the carbon and oxygen isotopic compositions of CO2 and H2 O in terms of moss water status and integrated isotope signals in cellulose., As external (capillary) water, and then mesophyll water, evaporated from moss tissue, assimilation rate, relative water content and the stable isotope composition of tissue water (δ18 OTW), and the CO2 and H2 O fluxes, were analysed. After drying, carbon (δ13 CC) and oxygen (δ18 OC) cellulose compositions were determined., During desiccation, assimilation and 13 CO2 discrimination increased to a maximum and then declined; δ18 OTW increased progressively by 8‰, indicative of evaporative isotopic enrichment. Experimental and meteorological data were combined to predict tissue hydration dynamics over one growing season. Nonsteady-state model predictions of δ18 OTW were consistent with instantaneous measurements., δ13 CC values suggest that net assimilation occurs at 25% of maximum relative water content, while δ18 OC data suggests that cellulose is synthesized during much higher relative water content conditions. This implies that carbon assimilation and cellulose synthesis (growth) may be temporally separated, with carbon reserves possibly contributing to desiccation tolerance and resumption of metabolism upon rehydration. [ABSTRACT FROM AUTHOR]

BACKGROUND: A major problem in common bean ( Phaseolus vulgaris L.) agriculture is the low yield due to terminal drought. Because common beans are grown over a broad variety of environments, the study of drought-resistant genotypes might be useful to identify distinctive or common mechanisms needed for survival and seed production under drought. RESULTS: In this study the relationship between terminal drought resistance and some physiological parameters was analysed using cultivars contrasting in their drought response from two different gene pools. Trials were performed in three environments. As expected, drought treatments induced a decrease in leaf relative humidity and an increase in leaf temperature; however, when these parameters were compared between susceptible and resistant cultivars under optimal irrigation and drought, no significant differences were detected. Similar results were obtained for chlorophyll content. In contrast, analysis of relative water content (RWC) and stomatal conductance values showed reproducible significant differences between susceptible and resistant cultivars grown under optimal irrigation and drought across the different environments. CONCLUSIONS: The data indicate that drought-resistant cultivars maximise carbon uptake and limit water loss upon drought by increasing stomatal closure during the day and attaining a higher RWC during the night as compared with susceptible cultivars, suggesting a water balance fine control to achieve enough yield under drought. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

To investigate the genetic basis of drought tolerance in soybean ( Glycine max L. Merr.) a recombinant inbred population with 184 F2:7:11 lines developed from a cross between Kefeng1 (drought tolerant) and Nannong1138-2 (drought sensitive) were tested under water-stressed and well-watered conditions in field and greenhouse trials. Traits measured included leaf wilting coefficient, excised leaf water loss and relative water content as indicators of plant water status and seed yield. A total of 40 quantitative trait loci (QTLs) were identified: 17 for leaf water status traits under drought stress and 23 for seed yield under well-watered and drought-stressed conditions in both field and greenhouse trials. Two seed yield QTLs were detected under both well-watered and drought-stressed conditions in the field on molecular linkage group H and D1b, while two seed yield QTLs on molecular linkage group C2 were found under greenhouse conditions. Several QTLs for traits associated with plant water status were identified in both field and greenhouse trials, including two leaf wilting coefficient QTLs on molecular linkage group A2 and one excised leaf water loss QTL on molecular linkage group H. Phenotypic correlations of traits suggested several QTLs had pleiotropic or location-linked associations. These results will help to elucidate the genetic basis of drought tolerance in soybean, and could be incorporated into a marker-assisted selection breeding program to develop high-yielding soybean cultivars with improved tolerance to drought stress. [ABSTRACT FROM AUTHOR]

Despite intensive research and breeding efforts, the physiological and quantitative genetic bases of drought tolerance are still poorly understood. The comparison of results obtained from different sources is also complex, because different testing methods may lead to controversial conclusions. This report discusses various drought stress experiments (hydroponics and in soil) in which the plant tolerance was studied at different developmental stages. Tests were performed in the germination, seedling and adult plant stages on the parental lines of five well-known barley-mapping populations. The results suggest that drought tolerance is a stage-specific trait and changes during the life cycle. The effect of drought stress depended not only on the duration and intensity of water deficiency, but also on the developmental phase in which it began. To induce the same type of stress and to obtain comparable tolerance information from the replications, it is recommended that drought stress should be induced at the same growth stage. Correlations between the traits, commonly associated with improved drought resistance (high relative water content under stress, proline accumulation, osmoregulation) with stress tolerance indexes, are also presented, while the advantages and disadvantages of the most frequently used screening methods are discussed. [ABSTRACT FROM AUTHOR]

This investigation was undertaken to compare the level of salinity tolerance of the newly bred CSR-30 basmati rice variety with that of the salinity sensitive HBC-19 and Pokkali rice varieties. Twenty-one-day-old hydroponically raised seedlings at 6 and 12 dS m−1 were investigated for growth, photosynthetic rate, chlorophyll content, ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) activity, relative water content (RWC), membrane stability index (MSI), lipid peroxidation, Na/K ratio and activities and gene expression of various isoforms of antioxidative enzymes. Salinity stress led to reduction in shoot length, leaf area, dry weight, RWC, MSI, rate of photosynthesis, chlorophyll content and Rubisco activity in all the three rice varieties. The levels of reduction in these parameters were maximal in HBC-19 followed by those in CSR-30 and Pokkali respectively. Cumulative superoxide dismutase (SOD) activity increased in Pokkali and CSR-30 in consonance with increase in salinity stress while it decreased in HBC-19. The Mn-SOD activity however, was enhanced in all three varieties in the presence of salinity stress while the activities of Fe-SOD, Cu/Zn-SOD and ascorbate peroxidase were decreased in HBC-19 when compared with CSR-30 and Pokkali. The activity of catalase (CAT) was higher in HBC-19 when compared with its activity in CSR-30 and Pokkali. The levels of gene expressions of the three isoforms of SOD ascertained by reverse transcriptase polymerase chain reaction were not necessarily indicative of the activities of the corresponding enzymes. Thus, despite the maximal enhancement in gene expression of Fe-SOD in HBC-19 in response to salinity stress, the activity of this enzyme in HBC-19 remained low. Similarly, despite a marginal increase in gene expression of Cu-Zn SOD in the three varieties, its activity was significantly higher in Pokkali and CSR-30 when compared with that in HBC-19. A significant enhancement in the activity of CAT at 12 dS m−1 in HBC-19 when compared with CSR-30 and Pokkali might confer a degree of tolerance to H2O2 stress in this variety in the presence of higher levels of NaCl at the seedling stage. [ABSTRACT FROM AUTHOR]

The effects of shade on the physiology of opuntias have received little attention, notwithstanding that shade regularly occurs in both wild stands and cultivated populations. This research evaluates the effects of shade on the physiology of cladodes of Opuntia ficus-indica, with and without daughter cladodes, as they are exposed to progressive drought. The stress caused by shade, drought and daughter cladodes reduced photosynthesis by mother cladodes and was associated with decreases in relative water content, parenchyma thickness and chlorophyll content. Shade exacerbated the physiological drought of mother cladodes imposed by daughter cladodes and by reduced soil water content. [ABSTRACT FROM AUTHOR]

Genetic differences in osmotic adjustment (OA) have been reported among chickpea ( Cicer arietinum) cultivars. In this study eight advanced breeding lines (ABLs) derived from a cross between CTS 60543 (high OA) and Kaniva (low OA) and Tyson (medium OA) and Kaniva, along with the parents, were evaluated for OA, leaf carbohydrate composition and leaf gas exchange under dryland field conditions in India. The water potential (WP) decreased to lower values (less than −2.5 MPa) in Tyson, M 110 and M 86 than in the other genotypes. With decrease in WP, OA increased by 0.5 MPa in Kaniva and CTS 60543 to 1.3 MPa in M 55. As the decrease in WP varied with genotype, when OA was regressed against WP M 39 and M 55 had greater increases in OA with decrease in WP than the remaining nine genotypes, including the parents. As WP decreased, leaf starch content decreased while total soluble sugars, hexoses and sucrose increased: the decrease in starch was much smaller in M 93 and M 129 than in Tyson and M 51, but genotypic differences could not be detected in the increase in total sugars, hexoses or sucrose. The rates of photosynthesis and transpiration decreased as the WP became more negative, but M 129 reached low rates of photosynthesis (2 μmol m−2 s−1) and transpiration at a WP of −1.7 MPa, whereas Tyson reached the same low rate at −2.4 MPa. While OA varied among the chickpea genotypes, the differences were not associated with the changes in carbohydrate composition or the rates of gas exchange at low values of WP. Further, the degree of OA of the 11 genotypes was not the same as when they were selected for differences in OA under rainout shelter conditions in the field in Australia, suggesting that OA may show poor stability depending upon the stress level, location or physiological stage of the plant. This suggests that OA is not a valuable drought-resistance trait to select for in chickpea breeding programmes. [ABSTRACT FROM AUTHOR]

Rab17 is a Late Embryogenesis Abundant (LEA) protein from maize, which accumulates largely during embryogenesis and also in vegetative tissues when subjected to stress conditions. We have analysed the effect of Rab17 expression under a constitutive promoter in vegetative tissues of transgenic Arabidopsis thaliana plants. These transgenic plants have higher sugar and proline contents, and also higher water loss rate under water stress. In addition, these plants are more tolerant than non-transformed controls to high salinity and recover faster from mannitol treatment. Our results point to a protective effect of Rab17 protein in vegetative tissues under osmotic stress conditions. [ABSTRACT FROM AUTHOR]

Summary Experimental studies on CO2 assimilation of mesophytic C3 plants in relation to relative water content (RWC) are discussed. Decreasing RWC slows the actual rate of photosynthetic CO2 assimilation (A) and decreases the potential rate (Apot). Generally, as RWC falls from c. 100 to c. 75%, the stomatal conductance (gs) decreases, and with it A. However, there are two general types of relation of Apot to RWC, which are called Type 1 and Type 2. Type 1 has two main phases. As RWC decreases from 100 to c. 75%, Apot is unaffected, but decreasing stomatal conductance (gs) results in smaller A, and lower CO2 concentration inside the leaf (Ci) and in the chloroplast (Cc), the latter falling possibly to the compensation point. Down-regulation of electron transport occurs by energy quenching mechanisms, and changes in carbohydrate and nitrogen metabolism are considered acclimatory, caused by low Ci and reversible by elevated CO2. Below 75% RWC, there is metabolic inhibition of Apot, inhibition of A then being partly (but progressively less) reversible by elevated CO2; gs regulates A progressively less, and Ci and CO2 compensation point, Γ rise. It is suggested that this is the true stress phase, where the decrease in Apot is caused by decreased ATP synthesis and a consequent decreased synthesis of RuBP. In the Type 2 response, Apot decreases progressively at RWC 100 to 75%, with A being progressively less restored to the unstressed value by elevated CO2. Decreased gs leads to a lower Ci and Cc but they probably do not reach compensation point: gs becomes progressively less important and metabolic limitations more important as RWC falls. The primary effect of low RWC on Apot is most probably... [ABSTRACT FROM AUTHOR]

Irrigation of wheat plants with seawater (10 and 25 %) led to significant increases in free and bound abscisic acid (ABA) in leaves, especially at 25 %. The relative water content (RWC) and water use efficiency (calculated from grain yield, WUEG, or from biomass yield, WUEB) of the seawater-irrigated plants were lower than those of the control. Grain pre-soaking in gibberellic acid (GA3), indole-3-acetic acid (IAA) or ABA reduced the levels of accumulated ABA (free and bound) produced by seawater irrigation. The stress imposed by seawater generally reduced yield and yield components of wheat plants and the effect was more pronounced at the higher level of seawater irrigation (25 %). Furthermore, seawater treatments decreased the carbohydrate content and increased the protein content of the developing grains. The effect of seawater treatments on ion concentrations in the developing grains was not consistent. The application of growth bioregulators appeared to mitigate the effect of seawater salinity stress on wheat productivity. GA3 was the most effective hormone in this regard. The economic yield (grain yield) had a strong positive correlation with RWC, WUEG, WUEB, plant height, shoot fresh and dry weight, grain number/main spike, kernel weight and harvest index. [ABSTRACT FROM AUTHOR]

Sunflower seedlings (Helianthus annuus hybrid Select) were grown in a complete nutrient solution in the absence or presence of Cd2+ (10 and 20 μM). Analyses were performed to establish whether there was a differential effect of Cd2+ on mature and young leaves. After 7 d the growth parameters as well as the leaf area had decreased in both mature and young leaves. Accumulation of Cd2+ in the roots exceeded that in the shoots. Seedlings treated with Cd2+ exhibited reduced contents of chlorophyll and CO2 assimilation rate, with a greater decrease in young leaves. The photochemical efficiency of photosystem II (PSII) was not altered by Cd2+ treatment in either mature or young leaves, although during steady-state photosynthesis in young leaves there was a significant alteration in the following parameters: quantum yield of electron transport by PSII (ΦPSII), photochemical quenching (qp), non-photochemical quenching (qNP), and excitation capture efficiency of PSII (Φexc). [ABSTRACT FROM AUTHOR]

ABSTRACTTurgid pieces of mature maize roots were dried in air and progressive changes in their relative water content (RWC) determined. Viability was tested by reproducibility of the drying curves after dehydration to successively lower RWCs. After reaching a chosen RWC, the pieces were rehydrated (approximately 2 h), and a 2nd and 3rd dehydration curve measured. Each drying curve was characterized by two parameters (a scale parameter λ, and a shape parameter β) of a survivorship function, which is a linear function of time. The parameter λ is more informative, and does not change in successive dehydrations for RWC > 0·4, suggesting no irreversible damage to the roots. Damage and death were indicated by divergences of λ in successive dehydrations to RWC = 0·35–0·15. Cryo-analytical microscopy confirmed these data while indicating specifically death of 50 and 100% of cortical cells at RWC 0·30 and 0·15, respectively, and survival of 50% or more of sieve tubes, pericycle and vascular parenchyma cells at root RWC as low as 0·15. This pattern of stelar cell survival may allow roots to preserve their capacity for renewal of axial conductivity and branch root development following periods of severe water stress. [ABSTRACT FROM AUTHOR]

summary: We report the changes in CO2 assimilation, potential photochemical activity (as measured by slow fluorescence), photosynthetic pigment concentrations, and dark respiration of two desiccation‐tolerant (DT) lichens (Cladonia convoluta (Lam.) P. Cout. and C. furcata (Huds.) Schrad.), and a DT moss (Tortula ruralis (Hedw.) Gaertn. ssp. ruralis) during slow drying, and on rehydration following a 12 h period of desiccation. Initially there was a two to fourfold increase in net CO., assimilation due to reduction of CO2‐diffusion resistance by elimination of excess water. Optimum water content for photosynthesis was 100–150 % of dry mass (DM) in C. convoluta, c. 100 % DM in C. furcata, and 120–200 % DM in T. ruralis. The intensity of maximum and steady‐state slow fluorescence showed little change above water contents of 56%, DM in the lichens and 73 % DM in T. ruralis (corresponding to c. 30–40 % cell relative water content), but fell sharply at lower water content. The variable duorophyll‐fluorescence decrease ratio (Rfd) at 690 nm peaked at 56 % DM water content in the two lichens, and at 45% DM in T. ruralis. Photochemical activity ceased at the same point in the experiments as CO, assimilation; dark respiration ceased only when desiccation was complete. In all three species, the photosynthetic apparatus remained in a fully and quickly recoverable state. Chlorophyll and carotenoid concentrations remained substantially unaltered throughout. On rehydration, chlorophyll fluorescence parameters returned within 30 min to pre‐desiccation levels, and photosynthesis recovered fully and rapidly (< 1 h). All three species attained a positive carbon balance within 20 min of re‐moistening, in spite of high rates of dark respiration. The results confirm the significance of extracellularly‐stored water to poikilohydric DT lichens and bryophytes. The measurements, in conjunction with published data on the full‐turgor water content of similar mosses and lichens, show that the cell‐physiological response of photosynthesis to water deficit is not greatly different from that of either normal or DT vascular plants. Small plant size and small cell volume in DT lichens and mosses, together with rapid recovery of photosynthesis after desiccation, allow the plants to utilize the small amounts of intermittently available water from brief showers or dew. [ABSTRACT FROM AUTHOR]

We report the changes in CO2 assimilation, potential photochemical activity (as measured by slow fluorescence), photosynthetic pigment concentrations, and dark respiration of two desiccation-tolerant (DT) lichens (Cladonia convoluta (Lam.) P. Cout. and C. furcata (Huds.) Schrad.), and a DT moss (Tortula ruralis (Hedw.) Gaertn. ssp. ruralis) during slow drying, and on rehydration following a 12 h period of desiccation. Initially there was a two to fourfold increase in net CO2 assimilation due to reduction of CO2-diffusion resistance by elimination of excess water. Optimum water content for photosynthesis was 100-150% of dry mass (DM) in C. convoluta, c. 100% DM in C. furcata, and 120-200% DM in T. ruralis. The intensity of maximum and steady-state slow fluorescence showed little change above water contents of 56% DM in the lichens and 73% DM in T. ruralis (corresponding to c. 30-40% cell relative water content), but fell sharply at lower water content. The variable chlorophyll-fluorescence decrease ratio (Rfd) at 690 nm peaked at 56% DM water content in the two lichens, and at 45% DM in T. ruralis. Photochemical activity ceased at the same point in the experiments as CO2 assimilation; dark respiration ceased only when desiccation was complete. In all three species, the photosynthetic apparatus remained in a fully and quickly recoverable state. Chlorophyll and carotenoid concentrations remained substantially unaltered throughout. On rehydration, chlorophyll fluorescence parameters returned within 30 min to pre-desiccation levels, and photosynthesis recovered fully and rapidly (< 1 h). All three species attained a positive carbon balance within 20 min of re-moistening, in spite of high rates of dark respiration. [ABSTRACT FROM AUTHOR]

Activities of nitrate reductase, glutamine synthetase along with rate of photosynthesis, chlorophyll content, soluble protein, relative water content, transpiration and diffusion resistance were estimated in wheat cv. C306 at anthesis stage under irrigated and moisture-stress condition and two levels (0.1 and 1.0 ppm) of homobrassinolide application. Yield and yield attributing parameters were recorded at harvest. Moisture-stress adversely affected relative water content, transpiration, net photosynthesis, nitrate reductase and glutamine synthetase activity, chlorophyll and soluble protein content. Homobrassinolide application increased leaf relative water content and transpiration and decreased diffusion resistance in water-stressed and recovered plants. Homobrassinolide application also had positive effect on nitrate reductase and glutamine synthetase activities, photosynthesis, chlorophyll and total soluble protein content in stressed, irrigated and revived plants. The beneficial effect was also observed on grain yield and yield attributing parameters such as grain number per ear, 1000 grain weight, ear number per plant and harvest index. It was concluded that homobrassinolide induced promotion in metabolic activity was mediated through increased enzyme protein synthesis as well as uptake of water resulting in enhanced relative water content under moisture-stress. [ABSTRACT FROM AUTHOR]

Previous findings indicated that leaf conductance and net photosynthesis were positively correlated with water status (relative water content) of tissue‐cultured shoots and plantlets, and that acclimatization was associated with a reduction in leaf conductance and transpiration. In the present study, the effect of acclimatization on plant water status after plants were removed from culture and transplanted in soil, as well as the relation of water status with survival and growth after acclimatization were determined. Tissue‐cultured plantlets (Malus pumila cv. Greensleaves) were acclimatized by exposure to a 4‐day gradual reduction in humidity before they were transplanted. Once plants were transplanted, acclimatized plants maintained a higher relative water content than nonacclimatized plants, probably because of a lower initial stomatal conductance and less transpiration. High plant water status, as indicated by high relative water content, appeared to be an important factor for both plant survival and growth after the plants were transplanted. Higher water status was associated with higher growth rates and net assimilation rates. The differences in gas exchange, water relations and growth characteristics between plantlets in vitro and at 4 weeks after they were transplanted were also studied. Compared to in vitro plants, transplanted plants had a higher water status and higher leaf conductance and net photosynthesis. There was also an increase in the leaf area ratio (leaf area to plant biomass ratio) after they were transplanted which might have contributed to the higher net assimilation rate in transplanted compared to in vitro plants. [ABSTRACT FROM AUTHOR]

Susceptibility of alfalfa (Medicago sativa L. cv. Aragón) nodules and leaves to water stress has been investigated. Nodule acetylene reduction activity (ARA), leaf CO2, exchange rate (CER) as well as soluble protein, proline and total soluble sugar (TSS) contents were determined during drought. Water status was estimated as water potential (ψw) and Relative water content (RWC) of the respective tissues. Maximum rates of ARA required higher ψw than CER. Nodules had lower RWC ψw a given than leaves. Water stress reduced soluble protein content in both tissues; however, the decline in soluble protein content was detected at greater ψw in nodules than in leaves. Proline and TSS increased in leaves and nodules, and again the threshold ψw triggering such accumulation was higher in nodule tissues. Our results suggest that alfalfa nodules are more susceptible to water shortage than leaves. Effects of accumulated TSS and proline upon leaf and nodule physiology are discussed in relation to protein stability (proline), pH control (proline) and osmotic adjustment (proline and TSS). The TSS accumulation induced by water stress suggests that substrate shortage would not be the primary effect of drought on nodule activity. [ABSTRACT FROM AUTHOR]

The long delayed maturation of the late metaxylem of maize (Zea mays) roots imposes a high-resistance barrier between the immature apices and the negative water potential of the leaves. These apices (20+ cm) bear strongly adhering soil sheaths to within 0.5 to 2 cm of the distal end. It was hypothesized that the sheathed immature apices should show less response to transpiration stress than bare regions. Measurements were made of the relative water content (RWC) of the sheathed and bare zones of the axile roots, both at different ages of the plant, and early and late in the day's transpiration. Sheathed roots maintained a steady RWC of about 83% irrespective of age or transpiration. Bare roots had RWCs of about 63% in the morning, but this fell to 55% in the afternoon. The first-order branches on the bare roots in the morning had still lower values of RWC, near 50%. Plots of RWC against water potential were indistinguishable for the three root types. It is concluded that the immature apices are indeed relatively isolated from the fluctuating tensions in the stem xylem, and that these tensions reduce the water content of bare roots and their branches to low values. [ABSTRACT FROM AUTHOR]

Seasonal and diurnal measurements of leaf water potential (ψL), relative water content (RWC) and stomatal conductance (gs) were made in the field on 19-year old Prunus salicina (L.) cv. Santa Rosa, a deciduous fruit tree species, irrigated with 3 different concentrations of saline water over a 3 year period (1985-1987). With the exception of stage III of fruit growth, little or no treatment difference in ψL, leaf turgor potential (ψP ), or RWC was noted during the day. Seasonal averages of morning (0700-0906) and afternoon (1500-1700) ψP did not decline with increasing salinity, indicating long-term osmotic adjustment in this species. Maintenance of leaf water status under saline conditions was in part a consequence of increased stomatal closure, with a subsequent reduction in leaf transpiration rate. However, during stage III of fruit growth, an increase in mean afternoon (1200-1700) stomatal conductance of 26-117%, independent of salinity treatment, was observed in 1985 and again in 1987. Higher conductance values during this period may be associated with rapid fruit expansion and greater assimilate demand. The observed increase in conductance resulted in greater leaf water loss and larger measured differences in midday ψL between salinity treatments. This research indicates that for Prunus salicina in the field, salinity stress resulted in leaf water deficits only during the final period of fruit expansion and ripening. [ABSTRACT FROM AUTHOR]

Six lines of sorghum (Sorghum bicolor L. Moench) with differing drought resistance (IS 22380, ICSV 213, IS 13441 and SPH 263, resistant and IS 12739 and IS 12744, susceptible) were grown under field conditions in the semi-arid tropics and analysed for proline and nitrate reductase activity (NRA; EC 1.6 6.1) during a mid-season drought. The resistant lines accumulated high levels of proline, while the susceptible lines showed no significant proline accumulation. Most of the proline was accumulated after growth of the plants had ceased. In a separate greenhouse experiment, most of the proline was found in the green rather than the fired portions of leaves. The levels returned to that of irrigated controls within 5 days of rewatering. Proline levels increased as leaf water potential and relative water content fell, and there was no apparent difference among the different sorghum lines with change in plant water status. Susceptible lines accumulated less proline than resistant lines as leaf death occurred at higher water potentials. Proline accumulation may, however, contribute to the immediate recovery of plants from drought. Leaf NRA reached high levels at about 35 days after sowing in both the stressed and irrigated plants, after which it declined. The decline in NRA was more pronounced in the stressed than in the irrigated plants and closely followed changes in the growth rate. Upon rewatering, NRA increased several-fold in all the lines and, in contrast to proline accumulation, genotypic differences in NRA were small, both during stress and upon rewatering. The high sensitivity of NRA to mild drought stress was reflected in the rapid decline of activity with small changes in leaf water potential and relative water content. The results are discussed in the light of a possible role for proline during recovery from drought, and the maintenance of NRA during stress and its recovery upon rewatering. [ABSTRACT FROM AUTHOR]

Two species of jute plants Corchorus capsularis L. (cv. JRC 212) and C. olitorius L. (cv. JRO 632) were subjected to water stress for 2 and 4 days by withholding water. The relative water content (RWC) decreased in both plants under water stress but to a greater extent in C. olitorius. The C. olitorius seedlings also showed greater membrane injury than C. capsularis seedlings under water stress as was evident from injury index data. Water stress increased glycolate oxidase (EC 1.1.3.1.) activity more in C. olitorius than in C. capsularis. The activity of superoxide dismutase (SOD, EC 1.15.1.1.) and catalase (EC 1.11.1.6.) decreased under water stress and their decrease was higher in C. olitorius than in C capsularis. The level of hydrogen peroxide and lipid peroxidation also increased in both plants under water stress and the increase was higher in C. olitorius than in C. capsularis seedlings. Under comparable external water stress, C. capsularis seedlings showed lower membrane damage, lower H2O2 accumulation and lower lipid peroxidation than C. olilorius which may be taken as indicative of higher water stress tolerance capacity of the former. [ABSTRACT FROM AUTHOR]

Pressure chamber (PC) and thermocouple pyschrometer (TP) were used to determine leaf water potential in tomato (Lycopedrsicon esculentum Mill.), eggplant (Solanum melongena L.) and bean (Phaseolus vulgaris L.) seedlings subjected to normal watering regime, drought or chilling temperature. The PC readings were corrected for apoplastic osmotic potential. Similar results were obtained in all species. In unchilled plants, the PC and TP measurements corresponded within a potential range of -0.1 to -2.5 MPa, but discrepancies between the two methods often occurred in chilled plants, with PC water potentials 0.2 to 1.4 MPa higher (less negative) than TP values. The PC measurements appeared spuriously high in chilled plant. In droughted plants leaf dehydration occurred in both the blade and the petiole, whereas in chilled plants, water deficit was generally observed only in the blade. [ABSTRACT FROM AUTHOR]

Barley varieties were screened for their efficient drought enduring ability and associated characters which may be useful in breeding programmes. The characters studied were: relative water content, content of proline, chlorophyll stability index (CSI), and percentage grain loss per plant due to water stress subjected to 10 days from jointing to boot stage. Proline and chlorophyll stability index were greatly associated with drought response (r = +0.54; -0.49), flag leaf area (r = +0.69; -0.51) and, to a certain extent, with leaf number (r = -0.35 and +0.34). Among the studied 19 varieties of barley, only three (DL 192, DL 36, DL 3) showed high enduring ability, of these the former two fall in the early, and the last one in the late flowering group. Morphological architecture of DL 192 had gathering type tiller (narrow tiller angle), wider and floppy leaves and it also bears physiological characters (high proline and high relative water content, and low value of chlorophyll stability index) necessary for drought resistance. DL 3 and DL 36 had dispersing type tiller (wider tiller angle) and erect leaf with good leaf area/plant, but unit leaf area was low in DL 3 (relates with shading behaviour reducing water loss). Other relations of drought resistance are briefly discussed in the text. An appraisal of the various traits revealed that high proline content, and low CSI (biochemical characters), earliness, larger flag leaf area and fewer leaves per plant (morphological characters) were directly correlated with productivity of the cultivars under drought conditions. These characters could be used as a guideline for breeding drought resistant cultivars of barley. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the effects of three chemical ameliorants, namely, cycocel, limewash and potassium chloride, on stomatal frequency, leaf water potential and relative water content in brinjal (Solanum melongena L.) plants under moisture stress conditions. Moisture stress imposed at three stages decreased stomatal frequency, the length and breadth of stomata, leaf water potential and relative water content. Of the chemical ameliorants investigated, potassium chloride performed best in terms of stomatal behaviour and leaf water potential, whereas cycocel proved best in the case of relative water content. [ABSTRACT FROM AUTHOR]

With 1 figure and 4 tables Terminal drought induces preharvest aflatoxin contamination (PAC) in peanut. Drought resistance traits are promising as indirect selection tools for improving resistance to PAC. The objectives of this study were to determine the effects of terminal drought on PAC and to investigate the associations between surrogate traits for drought tolerance and PAC. Field tests under rainout shelters were conducted in the dry seasons 2004/2005 and 2005/2006. Eleven peanut genotypes were evaluated under irrigated and terminal drought conditions. Data were recorded for physiological traits, total biomass, pod yield, Aspergillus flavus colonization and PAC. ICGV 98305, ICGV 98330, ICGV 98348, ICGV 98353 and Tifton‐8 had low aflatoxin contamination in both years. Traits related to drought resistance were associated well with those related to PAC under drought conditions. Specific leaf area, relative water content, chlorophyll density and drought stress ratings are the best traits for use as indirect selection tools for lower PAC. Breeding for drought tolerance using these traits as selection criteria may help to accelerate progress in developing resistance to PAC. [ABSTRACT FROM AUTHOR]