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Root-hemiparasitic plants of the genus Rhinanthus acquire resources through a water-wasting physiological strategy based on high transpiration rate mediated by the accumulation of osmotically active compounds and constantly open stomata. Interestingly, they were also documented to withstand moderate water stress which agrees with their common occurrence in rather dry habitats. Here, we focused on the water-stress physiology of Rhinanthus alectorolophus by examining gas exchange, water relations, stomatal density, and biomass production and its stable isotope composition in adult plants grown on wheat under contrasting (optimal and drought-inducing) water treatments. We also tested the effect of water stress on the survival of Rhinanthus seedlings, which were watered either once (after wheat sowing), twice (after wheat sowing and the hemiparasite planting) or continuously (twice and every sixth day after that). Water shortage significantly reduced seedling survival as well as the biomass production and gas exchange of adult hemiparasites. In spite of that drought-stressed and even wilted plants from both treatments still considerably photosynthesized and transpired. Strikingly, low-irrigated plants exhibited significantly elevated photosynthetic rate compared with high-irrigated plants of the same water status. This might relate to biochemical adjustments of these plants enhancing the resource uptake from the host. Moreover, low-irrigated plants did not acclimatize to water stress by lowering their osmotic potential, perhaps due to the capability to tolerate drought without such an adjustment, as their osmotic potential at full turgor was already low. Contrary to results of previous studies, hemiparasites seem to close their stomata in response to severe drought stress and this happens probably passively after turgor is lost in guard cells. The physiological traits of hemiparasites, namely the low osmotic potential associated with their parasitic lifestyle and the ability to withstand drought and recover from the wilting likely enable them to grow in dry habitats. However, the absence of osmotic adjustment of adults and sensitivity of seedlings to severe drought stress demonstrated here may result in a substantial decline of the hemiparasitic species with ongoing climate change. [ABSTRACT FROM AUTHOR]

The effects of water deficit on growth, nodulation, and several physiological and biochemical processes in six symbiotic combinations involving three Moroccan alfalfa (Medicago sativaL.) populations (Tafilalet1, Adis-Tata and Demnate2), an American Moapa variety and two rhizobial strains (RhL9 and RhL10) were studied. The experiment was conducted under greenhouse conditions. Seedlings were separately inoculated with the suspension of two rhizobial strains and grown under two irrigation regimes: 80% of field capacity (optimal irrigation) and 40% of field capacity (water deficit). The water stress was applied for five weeks and the agro-physiological and biochemical parameters related to water deficit tolerance were assessed. The results showed that the water deficit had significantly reduced the height of the plants, the dry biomass and nodulation. This constraint also negatively affected the relative water content of leaves, the membrane permeability, the stomatal conductance, the maximum quantum yield of photosystem II, the time to reach maximum fluorescence, the total chlorophyll content and the total nitrogen content. Comparison among the tested symbiotic combinations showed that their behaviors were significantly different. Under drought, oasis populations Ad and Ta maintained high PS II efficiency, membrane stability, relative water content, chlorophyll and nitrogen content in comparison to the mountain one Dm2 and the American Moapa variety. These parameters were maintained at adequate levels in the plants inoculated with the rhizobial strain RhL9 that showed a tolerance to water deficit conditions. [ABSTRACT FROM AUTHOR]

Eucalyptus genus is the most widely planted hardwood tree, which productivity and development are limited by low water availability. Plant drought tolerance can be managed by adopting strategies, such as the exogenous application of salicylic acid. The main objective of the present study was to assess whether the exogenous foliar salicylic acid application would ameliorate the damages of water deficit on Eucalyptus globulus plants. Plants were watered at 70% (well water) or 15% (water deficit) of field capacity and four concentrations of salicylic acid (0, 0.75, 2.5 and 5.0 mM) were applied. Water potential, total chlorophylls and carotenoids contents, chlorophyll fluorescence parameters, leaf gas exchange, malondialdehyde, total soluble sugars, starch and total phenols contents were measured. The global hormonal content was quantified by ultra-performance liquid chromatography–mass spectrometry and specific local dynamics of indolacetic acid and abcisic acid were detected by immunolocalization in leaves. A multivariate statistical approach was used to get an overview of the plant physiological status. E. globulus water deficit response included growth rate decline associated with reduced in both water potential and leaf gas exchange parameters. Plant water deficit defence strategies led to an increase in total chlorophylls and carotenoids contents, lipid peroxidation, phenols and total soluble sugars. Six from the 18 hormones detected increased in water deficit plants. Exogenous salicylic acid application improved water deficit tolerance of E. globulus by improving water potential with a positive impact in primary metabolism (photosynthetic rate, soluble sugars) but also in secondary metabolism and defence mechanisms (higher total phenols and less lipid peroxidation) in the highest salicylic acid concentrations. Also, changes in endogenous levels of abscisic and salicylic acids, gibberellins 4 and 7, and specific cytokinins were found in water deficit plants with salicylic acid application. Our results indicated that salicylic acid application could be a potential chemical priming strategy to ameliorate water deficit effects on E. globulus plants. [ABSTRACT FROM AUTHOR]

Little is known about the physiological mechanisms underlying plant responses and their ability to recover from water stress, especially responses that concern the root system. The effect of water stress on K + and water flows in excised roots as well as the relationship of these flows with water stress tolerance was studied in six sunflower ( Helianthus annuus L.) cultivars. Plants growing in a growth chamber were subjected to water stress by deficit irrigation for 15 days. After this period, the plants were re-irrigated and the exudates from the excised roots were collected. Water stress reduced the shoot growth of all plants, although differences were observed among the cultivars. While water stress stimulated the water flow in the excised roots of all cultivars, K + (Rb + ) uptake by the root and its discharge into the xylem was promoted only in those cultivars that were more susceptible to water stress. The same effect was observed when plants were subjected to water stress using polyethylene glycol (PEG) 6000. The promotion of both K + and water flows could be considered as a mechanism to tolerate water stress, through which the plant restores cell turgidity, shoot water status and plant growth after a water stress period. [ABSTRACT FROM AUTHOR]

Cuticular wax covers aerial organs of plants and functions as the outermost barrier against non-stomatal water loss. We reported here the functional characterization of the Glossy1(GL1)-homologous gene OsGL1-3 in rice using overexpression and RNAi transgenic rice plants. OsGL1-3 gene was ubiquitously expressed at different level in rice plants except root and its expression was up-regulated under ABA and PEG treatments. The transient expression of OsGL1-3–GFP fusion protein indicated that OsGL1-3 is mainly localized in the plasma membrane. Compared to the wild type, overexpression rice plants exhibited stunted growth, more wax crystallization on leaf surface, and significantly increased total cuticular wax load due to the prominent changes of C30–C32 aldehydes and C30 primary alcohols. While the RNAi knockdown mutant of OsGL1-3 exhibited no significant difference in plant height, but less wax crystallization and decreased total cuticular wax accumulation on leaf surface. All these evidences, together with the effects of OsGL1-3 on the expression of some wax synthesis related genes, suggest that OsGL1-3 is involved in cuticular wax biosynthesis. Overexpression of OsGL1-3 decreased chlorophyll leaching and water loss rate whereas increased tolerance to water deficit at both seedling and late-tillering stages, suggesting an important role of OsGL1-3 in drought tolerance. [ABSTRACT FROM AUTHOR]

Durum wheat is susceptible to terminal drought which can greatly decrease grain yield. Breeding to improve crop yield is hampered by inadequate knowledge of how the physiological and metabolic changes caused by drought are related to gene expression. To gain better insight into mechanisms defining resistance to water stress we studied the physiological and transcriptome responses of three durum breeding lines varying for yield stability under drought. Parents of a mapping population (Lahn x Cham1) and a recombinant inbred line (RIL2219) showed lowered flag leaf relative water content, water potential and photosynthesis when subjected to controlled water stress time transient experiments over a six-day period. RIL2219 lost less water and showed constitutively higher stomatal conductance, photosynthesis, transpiration, abscisic acid content and enhanced osmotic adjustment at equivalent leaf water compared to parents, thus defining a physiological strategy for high yield stability under water stress. Parallel analysis of the flag leaf transcriptome under stress uncovered global trends of early changes in regulatory pathways, reconfiguration of primary and secondary metabolism and lowered expression of transcripts in photosynthesis in all three lines. Differences in the number of genes, magnitude and profile of their expression response were also established amongst the lines with a high number belonging to regulatory pathways. In addition, we documented a large number of genes showing constitutive differences in leaf transcript expression between the genotypes at control non-stress conditions. Principal Coordinates Analysis uncovered a high level of structure in the transcriptome response to water stress in each wheat line suggesting genome-wide co-ordination of transcription. Utilising a systems-based approach of analysing the integrated wheat’s response to water stress, in terms of biological robustness theory, the findings suggest that each durum line transcriptome responded to water stress in a genome-specific manner which contributes to an overall different strategy of resistance to water stress. [ABSTRACT FROM AUTHOR]

Highlights: [•] Physio-morphological traits in sweet potato were declined under water-deficit stress. [•] Yield traits of water-deficit shock in sweet potato were dropped. [•] Reduction in physio-morphological characteristics plays a role as effective indices. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oryza spp. have evolved exceptional capabilities for tolerance to water submergence. [•] The SUB1A gene is a key determinant of submergence tolerance and survival. [•] Geographical and historical data suggest introgression of SUB1A-1 from wild into domesticated rice. [•] A distinct mechanism for submergence survival is probably present in CC genome wild rice lacking SUB1A. [Copyright &y& Elsevier]

Highlights: [•] Prunus cerasifera somaclonal variant induces short term flooding tolerance in peach. [•] Anatomical and physiological modifications occur in Prunus rootstock anoxic tolerant. [•] The isogenic variant is a profitable tool to identify anoxic tolerant DNA sequences. [ABSTRACT FROM AUTHOR]

ABSTRACT Quantification of succulence should ideally convey information about physiological function and yet also be straightforward to measure. While important aspects of succulence and its physiological consequences may be quantified using parameters derived from pressure-volume (P-V) curves, this technique applied to succulent tissues is difficult, time consuming and generally not suitable for large comparative datasets. We performed P-V curves on leaves of 25 taxa from across Caryophyllales and compared the results with direct measures of saturated water content (SWCmeas), the ratio of water mass at full saturation to tissue dry mass, for the same taxa. SWCmeas was significantly related to relative capacitance, the most physiologically relevant parameter describing tissue succulence. We developed a linear model describing SWCmeas as a function of relative capacitance and leaf volume, which is also supported when accounting for the phylogenetic relationships among taxa. These results indicate that SWCmeas is a suitable proxy for tissue succulence, and that both cellular properties and variation in gross morphology contribute towards a plant's relative water storage capacity. Quantifying SWCmeas across many taxa showing variation in tissue succulence will provide a new avenue for exploring the evolutionary dynamics of this important ecological adaptation. [ABSTRACT FROM AUTHOR]

Abstract: Withholding irrigation during last stages of onion crops is a common practice to minimize losses in storage due to rots. However, it is unclear whether extended periods of water deprivation may affect bulb postharvest behaviour. In this study we analyze the effects of water deficit during the crop cycle on bulb weight loss and sprouting during storage. Two experiments were conducted: one in a glasshouse with two onion cultivars subjected to three treatments of water availability (100%, 80% and 60% of field capacity); the other in the field, with one of these cultivars, subjected to two water availability treatments (dryland and irrigated twice during bulb filling). In both experiments five destructive samplings were done along crop development to assess plant height, number of green leaves, bulb and neck diameter, and whole-plant dry weight. Bulbs were harvested when 50% or more of the tops fell over. Harvested bulbs were classified by weight and then kept in a ventilated chamber at a mean temperature of 15°C and weighted every two weeks, up to six months. Water deficit led to a significant reduction of bulb size, an acceleration of sprouting and an increased rate of weight loss during storage in both cultivars and under both experimental conditions. Hence, restricted irrigation during extended periods may have negative effects on the conservation of stored onion bulbs which suggests the need to finely adjust water management in this crop. [Copyright &y& Elsevier]

Physiological responses of tef (Eragrostis tef (Zucc.)) to water stress during establishment, vegetative, flag leaf-1 and grain filling developmental stages were studied under glasshouse conditions in 2007 at Henfaes Research Centre, University of Wales, Bangor, UK using a ¿near-factorial¿ randomised complete block design. During each phenological phase plants were subjected to three levels of soil moisture tension viz., FC (¿0.12MPa), 50%FC (¿1.06MPa) and 25%FC (¿1.51MPa) until the completion of the specific phases and during the preceding and subsequent growth periods the stressed plants were irrigated to field capacity (FC). A maximum net CO2 assimilation (12.15¿molm¿2 s¿1) and transpiration (3.88mmolm¿2 s¿1) rates were recorded in the control treatment. Both levels of water stress during flag leaf-1 and grain filling development stages reduced these rates significantly. Severe water stress imposed during grain filling stage produced the lowest rates in both CO2 assimilation (¿2.80¿molm¿2 s¿1) and transpiration (0.15mmolm¿2 s¿1). Response curves of CO2 assimilation rates to PAR levels showed that initial photosynthetic efficiency (at light saturation point) of severely stressed tef was less (0.013¿molCO2/¿mol photons) than the corresponding efficiencies of other treatments (P <0.001). The grain filling stage of tef was the most sensitive to water stress and severe water stress caused significant reduction in physiological performance of tef. The low yielding nature of tef could be associated with its low light use efficiency which perhaps related to its leaf size and orientation. Therefore, improving tef light use efficiency should be a national agenda to improve its yielding potential. [Copyright &y& Elsevier]

In this article, the author discusses the physiology of leaf curling. According to the author, leaf curling is most often interpreted as a response to water stress. He explains that leaf curling represents a dynamic behavioral response in plants whereby the normal sunlight orientation of the two leaf surfaces may be reversed. The author suggests a regulatory signaling by light-activated stomata that is transmitted across the full thickness of the leaf and causes stomatal closure on the opposite.

The rhizome dynamics of Typha angustifolia in relation to water depth were investigated. Observations were made in two different stands, namely Akigase from April 2002 to December 2003, and Teganuma from April 2003 to December 2004. The mean rhizome length in the two stands was not significantly different but the mean rhizome diameter and biomass showed a significant difference. The larger rhizome diameter in Teganuma is seemingly an important adaptation to maintain effective aeration of the rhizome by reducing the internal resistance; while larger biomass helps survival under anoxia for longer periods of time, it also provides strong anchorage to the substrate. [ABSTRACT FROM AUTHOR]

Plants growing on both sides of the Tarim River in western China serve as a natural barrier containing the deserts and protecting the oasis, and their growth is greatly affected by water conditions in their local habitat. We studied the physiological responses of three different types plants (i.e. Populus euphratica Oliver, Tamarix ramosissima L., and Apocynum venetumas Linn) to changing groundwater levels by analyzing changes in chlorophyll, soluble sugar, proline (Pro), malondialdehyde (MDA), superoxide dismutase (SOD), peroxidase (POD), indoleacetic acid (IAA), giberellic acid, abscisic acid (ABA) and cytokinin (CK). Relationships between these physiological characteristics and groundwater levels were analyzed in order to assess the drought tolerance of the three plant species based on the values of average membership function. We found that MDA, SOD and ABA were more susceptible to changes in groundwater level, followed by POD, IAA and CK. Among the three plant species, Populus euphratica responded physiologically less to changing groundwater level than T. ramosissima and A. venetumas. (Managing editor: Ya-Qin Han) [ABSTRACT FROM AUTHOR]

Sticky fleabane, Inula viscosa , a wild perennial Asteracea widespread in the Mediterranean area, is characterized by high tolerance to water deficiency. In this study, plants of I. viscosa obtained from seedlings were grown in a controlled environment and irrigated from transplanting to flowering with salinized water at seven different NaCl concentrations (ECi = 0.5 to 52.1 dS m -1 ), in order to evaluate the salinity tolerance and the ion content (Na, Cl, N, P, K, Ca and Mg, as mg kg -1 of dry weight) within plant tissues (roots, basal stems, medium stems, apical stems, lateral shoots, basal and apical leaves). Data obtained showed for I. viscosa a marked tolerance to salt stress. A K/Na concentration ratio of 0.1 was in the tissues of the basal leaves, suggesting a mechanism of Na exclusion from the younger leaves and the apical stems. The results in the first growing year indicate that I. viscosa can grow and flower in saline conditions up to ECi = 52.1 dS m -1 , even if it shows a marked reduction of fresh and dry weight; although Inula viscosa cannot be defined an halophyte plant as Inula crithmoides , it can be considered suitable for programs of desertification control, considering its high fresh biomass production also in high salinity conditions. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the effect of partial rootzone drying (PRD) in comparison to conventional irrigation (CI) at both 0.8 and 0.4 crop evapotranspiration (ETc) on water relations, vegetative growth, yield, and fruit composition of mature Sauvignon blanc grapevines (Vitis vinifera L.) in the San Joaquin Valley of California, USA. Soil moisture decreased quickly on the dry side and was restored quickly on the wet side of PRD-treated vines after switching. There was no yield reduction while vegetative growth was reduced at 0.4 ETc. However, in contrast to published studies assuming and emphasizing the role of PRD, this study demonstrated that only an irrigation amount of 0.4 ETc reduced stomatal conductance, transpiration, pruning weight, number of lateral shoots, number of active growing points, and fruit titratable acidity (TA). It appears that the irrigation amount, not PRD, is the determining factor inducing water stress and reducing transpiration and vegetative growth. With vine water relations only occasionally affected and no improvement in vine performance and vine water use at the same irrigation amount, PRD is not recommended for winegrape production with Sauvignon blanc under similar climatic conditions and cultural practices as in this study. Commercial implementation of PRD as described in previous studies should not be recommended until PRD is proven advantageous over CI at the same irrigation amount. [ABSTRACT FROM AUTHOR]

Soybean [Glycine max (L.) Merr. cv. Essex] was grown from seed in a greenhouse under ultraviolet-B (UV-B. 280-320 nm) radiation supplied by filtered FS-40 sunlamps. On a weighted, total daily dose basis these plants received either 0 (control) or 2875 effective J m-2 day-1 UV-BBE. When weighted with the generalized plant action spectrum (Caldwell 1971), this simulated the solar ultraviolet-B irradiance expected to occur at College Park, Maryland, USA (39°N) in the event the global stratospheric ozone column is reduced by 23%. The effects of ultraviolet radiation on the photosynthetic recovery from water stress were measured with an infrared gas analyzer. These effects were examined in plants which were either well-watered or previously preconditioned to water stress, during two distinct phenological stages 01 development. During the early stages of soybean growth, enhanced levels of UV-B reduced net photosynthesis by 25%, and water stress also reduced photosynthesis to nearly the same extent (by 20%). The combination of these two stresses resulted in smaller biomass than that produced by plants exposed to either stress independently. Photosynthesis in older, larger plants was much more sensitive to water stress and was reduced by as much as 50-60% in non-preconditioned plants. Although non-irradiated, non-preconditioned (control) plants recovered to only within 60% of their pre-stressed value, preconditioned plants recovered to within 70-80% during the 3 day recovery period. Both water stress and UV-B radiation affected non-stomatal conductance, while stomatal conductance was primarily affected by water stress. [ABSTRACT FROM AUTHOR]

It is usually suggested that the effects of wind on plant growth and development are caused by water stress. The purpose of the work reported in this paper is to examine this suggestion by a series of experiments in a controlled environment wind tunnel. Cuticular conductance of Pinus contorta subjected to low and high wind‐speeds were determined by weighing detached needles on a microbalance. Although the needles collided with each other at the high wind‐speed, there was no effect on cuticular conductance, unlike results obtained elsewhere with broader‐leaved plants. The transpiration rates and needle conductances of whole plants were unaffected by exposure to wind or a gentle shaking treatment. Water potentials and pressure‐volume curves were determined on individual needles of Pinus contorta. Wind and shaking had no effect on total, solute, or pressure potentials, or in any of the parameters describing the pressure‐volume curves. It is concluded that the effects of these treatments on growth of Pinus contorta, reported in previous papers, are unlikely to be caused by tissue water stress. [ABSTRACT FROM AUTHOR]

Soybeans [Glycine max (L.) Merrill cv. Wayne] plants were subjected to an extended drying cycle in the field to investigate the leaf sensitivity to water deficits. Soybeans in irrigated plots were superior to those in non‐irrigated plots in the average size and number of leaflets per plant. Apparent differences in the leaf area distributions in the canopy seemed to be mediated by moisture stress effects associated with leaf senescence and light penetration in the lower depths of the canopy. A major decrease in leaf enlargement occurred near a leaf‐water potential of ‐8 bars, and at ‐ 12 bars, the growth was completely halted. Similar decreases were observed at a stomatal conductance of 0.4 cm/s and at 0.2 cm/s no enlargement was observed. [ABSTRACT FROM AUTHOR]

This study continues the investigations previously conducted as laboratory experiments. The results from the present study confirm our earlier observations made on alder seedlings concerning the effect of water stress, temperature and light on the net uptake of CO2. A variable that we could call the physiological water stress is proposed as a measure of the intrinsic factor of photosynthesis during and after drought. A physiological water stress builds up and discharges slowly and interacts strongly with temperature. Our mode! for the effects of physiological water stress, temperature, and light intensity explains satisfactorily the net uptake of CO2 in birch in the field. Thus, our earlier results concerning the effects of physiological water stress on photosynthesis are not artifacts generated by the unnatural laboratory environment. [ABSTRACT FROM AUTHOR]

The function of photosystem II (PSII) during desiccation was investigated via analysis of Chi a fluorescence emission in thalli from Parmelia quercina (Wilid.) Vainio, Parmelia acetabulum (Necker) Duby, Ramalina farinacea (L.) Ach., Pseudevernia furfuracea (L.) Zopf., and Evernia prunastri (L.) Ach. Water loss followed the same exponential pattern in all these species, the half time being dependent on species. Desiccation affected the fluorescence parameters. Dark-adapted maximum fluorescence (Fm), instantaneous fluorescence (Fo) and the ratio of variable (Fm-Fo) to Fm were dependent on water content and decreased in two distinct phases: a slow and apparently linear phase, followed by a more steep decline at low water content. Actual PSII photochemical yield (ΦPSII), non-photochemical quenching (NPQ), efficiency of photon capture (ΦPSII), and photochemical quenching (qp) remained nearly constant until 30% relative water content (RWC), decreasing rapidly thereafter. In contrast, increased NPQ appeared to occur only at water content values lower than 20%. Treatment of thalli with dithiothreitol (DTT) effectively reduced NPQ during desiccation and increased susceptibility to photoinhibition caused by exposure to high light as measured by dark recovery of the Fv/Fm, ratio. HPLC analysis showed that the level of the de-epoxidized xanthophyll cycle pigments antheraxanthin (Anth) and zeaxanthin (Zea) increased during lichen desiccation. The results point towards the existence of a photoprotective mechanism with the involvement of Zea and Anth in non-radiative dissipation of the desiccation-induced excess of energy. [ABSTRACT FROM AUTHOR]

Application of the growth retardant CCC to gladiolus plants resulted in stimulation of stem length, increased number of flowers per spike and a slight advancement of anthesis date. Leaves of treated plants were heavier that control and contained a higher amount of water and chlorophyll. The anthocyanin content in petals was also greatly increased. CCC had little or no effect on the content of the endogenous gibberellins in the acidic ethyl acetate fraction, but markedly increased the content of the native gibberellins in the aqueous fraction. The mode of action of CCC in plants is discussed on the basis of these results and a review of the literature. [ABSTRACT FROM AUTHOR]

The article presents a study which compares two basic methods for the measurement of leaf water deficit which includes Stocker's water deficit method (WD) (1929), and Weatherley's relative turgidity method (RT) (1950). It reports that the two methods were compared using Western Australian native species where in it was found that Wetherley's method gave lower values for relative water contents in the species tested. It notes that the WH method was used since there are no restrictions were imposed by leaf type or size. It lists the modifications on the original method to avoid possible errors.

The authors discuss the study conducted by D. W. Butler and colleagues on the potential effect of drag tolerance-avoidance trade-off exposed to wind and water in terrestrial environment versus plants. They say that the study reveals that aquatic plants experienced a larger drag by 25-times than terrestrial plants. Also investigated is the impact of strength versus streamlining trade-off on plants tissue and composition.