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Groundwater level is crucial for wetland plant growth and reproduction, but the extent of its effect on plant growth can vary along with changed precipitation and temperature at different seasons. In this context, we investigated the effect of two groundwater levels (10 cm vs. 20 cm depth) on growth and reproductive parameters of Carex cinerascens, a dominant plant species in the Poyang Lake wetland, during three seasons (spring, summer, and autumn) and during two consecutive years (2015 and 2016). Carex cinerascens showed low stem number, height, and individual and population biomass in summer compared to spring and autumn. 10 cm groundwater level was overall more suitable for plant growth resulting in higher stem height and biomass. However, the interactive effect between groundwater level and season clearly demonstrated that the effect of groundwater level on plant growth occurred mainly in autumn. After the withering of the plant population in summer, we observed that C. cinerascens growth recovered in autumn to similar values observed in spring only with 10 cm groundwater level. Consequently, we could deduce that lowering groundwater level in the studied Poyang Lake wetland will negatively impact C. cinerascens regeneration and growth particularly during the second growth cycle occurring in autumn. Additionally, our results showed that, independently of the season and groundwater level, population biomass of C. cinerascens was lower during drier year. Altogether, our findings suggest that water limitation due to both reduction in precipitation and decreased groundwater level during the year can strongly impact plant communities. [ABSTRACT FROM AUTHOR]

Understanding how trees respond to extreme events is important to predict how climate change will impact forests in the future. In this study, we report changes in radial growth and tree‐ring carbon (δ13C) and oxygen (δ18O) stable isotope ratios of Pseudotsuga menziesii (Douglas‐fir) in western Mexico. Tree growth was compared with δ13C and δ18O ratios recorded during dry and wet periods caused by El Niño‐Southern Oscillation since 1850. The three driest and three wettest events during the studied period caused tree growth decline of up to 50% followed by 6–10 years of slow recovery until baseline growth was regained. Wet events resulted in up to 17% growth increase, a positive effect that persisted for no more than 3–5 years. Stable isotope ratios recorded physiological adjustments that in some cases correlated significantly with tree growth. Excursions in tree‐ring Δ13C and δ18O isotope ratios suggest that trees cope with dry and wet periods with proportional but divergent adjustments in photosynthesis versus stomatal conductance. Notably, the intrinsic water‐use efficiency—that is, the ratio between carbon assimilation and water loss through transpiration—was positively correlated with tree basal growth only during dry periods. We found no significant correlations between growth and intrinsic water‐use efficiency during wet periods. Contrary to expectations, rising CO2 levels over the past ~160 years did not affect tree growth response to precipitation variability. Key Points: To quantify the response of Douglas‐fir trees to dry and wet events, we measured tree rings and C and O stable isotopes since 1850Tree growth decreased up to 50% following extreme drought events, an impact that lasted up to 10 yearsEach extreme wet event resulted in up to 17% of growth increase, an effect that lasted up to 5 years [ABSTRACT FROM AUTHOR]

Water availability is often described as one of the main drivers of phenology of tropical dry forests but experimental studies to identify the cues triggering phenological changes are few. In a greenhouse trial, we exposed seedlings of thirteen origins, seven from West and six from East Africa, respectively, of Adansonia digitata L.(baobab) to a well‐watered control treatment and a water withholding treatment in combination with exposure to three different daylengths (11.5, 12.0, and 12.5 hr). Responses were measured in terms of meristematic activity, number of leaves, and height growth followed over 6.5 months. Multi‐level mixed‐effects statistical models were used to analyze how environmental and inter‐population variables affected phenological behavior. Flushing was influenced by the daylength with the lowest degree of meristematic activity observed in the short daylength treatment. Daylength also influenced the number of leaves through an interaction with the water regime. The water regime influenced all variables through interactions with the origins. Seedlings subjected to water stress had higher meristematic activity, but initially lower numbers of leaves than continuously watered plants. Height growth in continuously watered plants was fastest or at par with water‐stressed plants, depending on the origin. Origins from West Africa tended to have higher meristematic activity and their phenology was found to be less influenced by water withholding than East African origins. There were no signs of significant differences between origins in their response to photoperiod. In conclusion, baobab seedlings show opportunistic behavior, setting leaves when water is available, but larger activity is found when days are long. We discuss the results in terms of triggering factors for baobab phenology and adaptation to specific environmental conditions at the site of origins. There are very few studies on triggering factors for phenology of dry zone tropical tree species, and even fewer studies that investigate how phenology is varying among origins in common garden experiments. In this study, we tested 13 baobab origins and their phenological response to drought stress and different daylengths. Our results demonstrate that both water availability and daylength influence flushing of leaves, and that origin react differently to these signals. [ABSTRACT FROM AUTHOR]

Contrasting phenotypes of foundation species are known to differentially affect understorey plants. However, there is little knowledge on both the mechanisms of competition (resource competition versus interference) of stress-tolerant phenotypes and the importance of indirect interactions. In an oromediterranean community from Mount Lebanon we assessed the effects on understorey forbs of two contrasting phenotypes, a tight competitive from stressful habitat and a loose facilitative from more benign habitat. In a dry south and a wet north exposure we assessed short-term resource effects removing shrub canopy and long-term soil effects (including litter interference) with the comparison of forb performances in adjacent naturally open areas vs no shrub. Indirect effects were quantified through the removal of grasses. Abundance, richness and biomass of forbs were measured in all treatments after one year of experiment, together with litter depth and soil moisture. We found strong direct negative soil effects of the tight phenotype on all forb performances and in particular in south exposure. These effects were due to litter interference on water availability, but not to resource competition. They were likely explained by the high hydrophobicity of organic matter accumulating in the stressful habitat of the tight phenotype. We also found an indirect competition of the loose phenotype for forb richness, due to its direct positive soil effect on competitive grasses, and in particular in south exposure. Our results improve our knowledge on the importance of litter interference in dry nutrient-poor habitats and the role of indirect interactions in phenotypic effects on understorey species. [ABSTRACT FROM AUTHOR]

Climate warming increases vulnerability to drought in Mediterranean water-limited forests. However, we still lack knowledge of the long-term physiological responses of coexisting pine species in these forests regarding their ability to cope with warming-induced drought stress., We investigated spatiotemporal patterns of tree performance for five isohydric pines with partially overlapping ecological niches in the eastern Iberian Peninsula along an altitudinal gradient: Pinus halepensis = Pinus pinaster ≤ Pinus nigra ≤ Pinus sylvestris ≤ Pinus uncinata., Using indexed tree-ring widths ( TRW i), we assessed the changes in the temporal coherence of radial growth (growth synchrony, â C) over the period 1902-2011 across three elevation belts: low ≈1100 m; mid = 1615 m; high = 2020 m. We also examined by mixed modelling whether TRW i showed an increased coupling with leaf-level gas exchange (inferred from indexed carbon isotope discrimination, Δ13C i) by enhanced stomatal regulation in response to an amplified regional drought stress., Increasingly negative annual water balances (decrease in annual precipitation minus evapotranspiration = −4·8 mm year−1; 1970-2011) prompted more synchronous growth of coexisting pines between low- and mid-elevation belts, with â C rising from 0·25 ± 0·04 (1902-1951) to 0·62 ± 0·05 (1962-2011). This effect was coupled with tighter stomatal regulation at mid-elevation as indicated by high correlations between TRW i and Δ13C i (>0·60 from the mid-1970s onwards) which resembled those found at low elevation. Simultaneously, TRW i vs. Δ13C i uncoupling occurred at the high-elevation belt across species., Weaker growth-climate relationships as elevation increased highlighted the major role of the altitude-dependent thermal gradient in growth responsiveness to drought; however, an intensified Δ13C i response to spring water availability across elevation belts observed from mid-1970s onwards suggested regional shifts in tree physiological activity linked to earlier seasonal drought impacts. Warming-induced drought stress is spreading to higher altitudes in Iberian pinewoods as multispecies growth is linked to progressively tighter stomatal control of water losses reflected in wood Δ13C. [ABSTRACT FROM AUTHOR]

Roots, the hidden half of crop plants, are essential for resource acquisition. However, knowledge about the genetic control of below-ground plant development in wheat, one of the most important small-grain crops in the world, is very limited. The molecular interactions connecting root and shoot development and growth, and thus modulating the plant's demand for water and nutrients along with its ability to access them, are largely unexplored. Here, we demonstrate that linkage drag in European bread wheat, driven by strong selection for a haplotype variant controlling heading date, has eliminated a specific combination of two flanking, highly conserved haplotype variants whose interaction confers increased root biomass. Reversing this inadvertent consequence of selection could recover root diversity that may prove essential for future food production in fluctuating environments. Highly conserved synteny to rice across this chromosome segment suggests that adaptive selection has shaped the diversity landscape of this locus across different, globally important cereal crops. By mining wheat gene expression data, we identified root-expressed genes within the region of interest that could help breeders to select positive variants adapted to specific target soil environments. [ABSTRACT FROM AUTHOR]

Droughts are expected to become more frequent and more intense under climate change. Plant mortality rates and biomass declines in response to drought depend on stomatal and xylem flow regulation. Plants operate on a continuum of xylem and stomatal regulation strategies from very isohydric (strict regulation) to very anisohydric. Coexisting species may display a variety of isohydricity behaviors. As such, it can be difficult to predict how to model the degree of isohydricity at the ecosystem scale by aggregating studies of individual species. This is nonetheless essential for accurate prediction of ecosystem drought resilience. In this study, we define a metric for the degree of isohydricity at the ecosystem scale in analogy with a recent metric introduced at the species level. Using data from the AMSR-E satellite, this metric is evaluated globally based on diurnal variations in microwave vegetation optical depth ( VOD), which is directly related to leaf water potential. Areas with low annual mean radiation are found to be more anisohydric. Except for evergreen broadleaf forests in the tropics, which are very isohydric, and croplands, which are very anisohydric, land cover type is a poor predictor of ecosystem isohydricity, in accordance with previous species-scale observations. It is therefore also a poor basis for parameterizing water stress response in land-surface models. For taller ecosystems, canopy height is correlated with higher isohydricity (so that rainforests are mostly isohydric). Highly anisohydric areas show either high or low underlying water use efficiency. In seasonally dry locations, most ecosystems display a more isohydric response (increased stomatal regulation) during the dry season. In several seasonally dry tropical forests, this trend is reversed, as dry-season leaf-out appears to coincide with a shift toward more anisohydric strategies. The metric developed in this study allows for detailed investigations of spatial and temporal variations in plant water behavior. [ABSTRACT FROM AUTHOR]

Screening for drought in soybean is often a bottleneck in plant breeding programmes. Sixteen genotypes were evaluated for drought tolerance during 2012, 2013 and 2014. The experiment was conducted in a split-plot design, and the main plots consisted of irrigated and water stress treatments, and subplots consisted of 16 genotypes. The average seed yield was highest in 2012 (1708 kg/ha), followed by 2014 (1364 kg/ha) while very low yields (958 kg/ha) were observed during 2013. The per cent reduction in average soybean yield under water stress conditions was maximum (43%) during 2014 followed by 2012 (40%) and 2013 (31%), respectively. The average yields of soybean genotypes also differed significantly, which ranged from 892 ( NRC 12) to 2008 kg/ha ( JS 97-52). The maximin-minimax approach was used to classify these genotypes, and only, one genotype was identified as drought resistant and high yielding ( EC 538828), three as tolerant and high yielding ( JS 97-52, EC 456548 and EC 602288) and none as low yielding and resistant, while the remaining 12 genotypes were found to be low yielding and susceptible to drought. [ABSTRACT FROM AUTHOR]

BACKGROUND Babyleaf salads such as spinach ( Spinacia oleracea L.) and spinach beet ( Beta vulgaris L. subsp. cicla var. cicla) are an important dietary source of antioxidants such as ascorbic acid (vitamin C). Such compounds may be important in disease prevention in consumers but the level of these compounds in leaves frequently declines after harvest. As such, methods to maintain antioxidant levels in fresh produce are being sought. RESULTS Irrigation deficits were used to apply water stress to S. oleracea and B. vulgaris plants. This treatment prevented postharvest decline of leaf ascorbic acid content in S. oleracea but not in B. vulgaris. Ascorbic acid levels in leaves at harvest were unaffected by the treatment in both species compared to well-watered controls. CONCLUSION We have shown that restricted irrigation provides a viable means to maintain leaf vitamin content after harvest in S. oleracea, an important finding for producers, retailers and consumers alike. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Experiments were conducted in outdoor, naturally sunlit, soil–plant–atmosphere research (SPAR) chambers using plants grown in pots. Drought treatments were imposed on potato plants (Solanum tuberosum cv. Kennebec) beginning 10 days after tuber initiation. A total of 23 out of 37 foliar metabolites were affected by drought when measured 11 days after initiating water stress treatments. Compounds that accumulated in response to drought were hexoses, polyols, branched chain amino acids (BCAAs) and aromatic amino acids, such as proline. Conversely, leaf starch, alanine, aspartate and several organic acids involved in respiratory metabolism decreased with drought. Depending upon harvest date, a maximum of 12 and 17 foliar metabolites also responded to either CO2 enrichment or diurnal treatments, respectively. In addition, about 20% of the measured metabolites in potato leaflets were simultaneously affected by drought, CO2 enrichment and diurnal factors combined. This group contained BCAAs, hexoses, leaf starch and malate. Polyols and proline accumulated in response to water stress but did not vary diurnally. Water stress also amplified diurnal variations of hexoses and starch in comparison to control samples. Consequently, specific drought responsive metabolites in potato leaflets were dramatically affected by daily changes of photosynthetic carbon metabolism. [ABSTRACT FROM AUTHOR]

Crown carbon gain is maximized for a given total water loss if stomatal conductance ( gs) varies such that the marginal carbon product of water (∂ A/∂ E) remains invariant both over time and among leaves in a plant crown, provided the curvature of assimilation rate ( A) versus transpiration rate ( E) is negative. We tested this prediction across distinct crown positions in situ for the first time by parameterizing a biophysical model across 14 positions in four grapevine crowns ( V itis vinifera), computing optimal patterns of gs and E over a day and comparing these to the observed patterns. Observed water use was higher than optimal for leaves in the crown interior, but lower than optimal in most other positions. Crown carbon gain was 18% lower under measured gs than under optimal gs. Positive curvature occurred in 39.6% of cases due to low boundary layer conductance ( gbw), and optimal gs was zero in 11% of cases because ∂ A/∂ E was below the target value at all gs. Some conclusions changed if we assumed infinite gbw, but optimal and measured E still diverged systematically in time and space. We conclude that the theory's spatial dimension and assumption of positive curvature require further experimental testing. [ABSTRACT FROM AUTHOR]

Rising atmospheric carbon dioxide concentration ([CO2]) has the potential to positively impact C3 food crop production by directly stimulating photosynthetic carbon gain (A), which leads to increased crop biomass and yield. Further stimulation of A and yield can result from an indirect mechanism in which elevated [CO2] decreases stomatal conductance and canopy water use, ameliorating drought stress. Experiments in open top chambers (OTC) and free air CO2 enrichment (FACE) facilities have enabled investigation of crop responses to elevated [CO2] in near natural, field conditions. Mechanistic understanding of physiological responses to elevated [CO2] has led to predictions that the stimulation of A, biomass production, and economic yield will vary with the temperature and water supply experienced by the crop. This study tested current assumptions about the relationships between relative responses of yield and biomass to elevated [CO2] and variation in growing season temperature and water inputs (precipitation plus irrigation). Growing season average temperature was not a good predictor of the magnitude of biomass and yield responses to elevated [CO2], contradicting the prediction that responses to elevated [CO2] would increase with increasing temperature due to the greater benefit from decreasing photorespiration. However, the prediction that the relative stimulation of yield by elevated [CO2] would be greatest in dry conditions was generally supported. Thus, a simple CO2 fertilization value is not appropriate for modeling future crop productivity under varying environmental conditions. Further studies are necessary across a broader range of environmental conditions in order to accurately predict how rising [CO2] will interact with temperature and drought stress and alter future crop production. [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]

The composition of high-molecular-weight glutenin subunit (HMW-GS) and low-molecular weight glutenin subunit (LMW-GS) in wheat (Triticum aestivum L) kernel affects the size of ~lutenin macropolymer (GMP), which is consid&ed the important flour quality traits in wheat. Three wheat cultivarswith differentend-use quali1ty were used to study the effects of water-nitrogen (W x N) management on relative HMW-GS and GMP contents. Under irrigation, increased levels promoted the accumulation of HMWand LMW-GS, GMP content, and the proportion of the larger particle of GMP, with higher yield and better end-use quality. Under rainfed conditions, increased N fertilizer also increased protein content in the three cultivars. As opposed to Gaochengo9Ol', 'Shannongl39l' and 'Taishan23' got higher HMWand LMW-GS contents and larger GMP particles, but reduced yields of both. Irrigation increased the yield markedly, the N application significantly affected the glutenin, but the W x N interaction was not significant. On one hand, increased N levels improved the dough development time by increasing the numbers of larger GMP particles and enhane of volume and surface area percentages on the other. It was suggested that the interaction as a complicated network and some individual effect might be important. When managing for wheat yield and quality, growers should first consider the water factor, then the N fertilizer factor to improve the end-use quality of wheat. [ABSTRACT FROM AUTHOR]

The depth of plant roots depends on a variety of conditions, including soil properties, vegetation type, nutrient availability, and climate. A water-optimal root depth is determined by equating the marginal carbon cost of deeper roots with the benefit of those roots to continued transpiration. This work compares the effect of two bounding strategies of plant uptake, conservative and intensive, on the water-optimal root depth and the response of that depth to changes in precipitation. While there are some differences between the models, both indicate similar responses of root depth to climate. The deepest roots are found in climates for which precipitation and potential transpiration are approximately equal, and root depths are more sensitive to changes in precipitation depth than frequency under dry conditions and more sensitive to rainfall frequency when the climate is wet. For all climate conditions, the water-optimal root depth is deeper and mean transpiration is lower when plant uptake is represented by the conservative model. These results highlight the explanatory power of water with respect to root depth and identify potential effects of a changing climate. [ABSTRACT FROM AUTHOR]

• The homoploid hybrid species Pinus densata is restricted to alpine habitats that exceed the altitude range of its two parental species, Pinus tabulaeformis and Pinus yunnanensis. Alpine habitats usually generate cold-induced water stress in plants. To understand the ecological differentiation between these three species, we examined their physiological responses to drought stress. • Potted seedlings of three species were subjected to low, mild, moderate and severe water stress in an automatic-controlled glasshouse. Fifteen indicators of fitness were measured for each species in each treatment, and most of these decreased as drought increased. • Pinus densata exhibited higher fitness than both parental species in terms of total dry mass production (TDM) and long-term water use efficiency (WUEL) across all treatments; several other ecophysiological traits were also extreme but not across every treatment, and not always in the highest stress treatment. • These results indicate that extreme characters that have become well fixed in P. densata, confer a faster seedling growth rate and more efficient water use, which in turn should confer increased drought tolerance. These traits of P. densata likely promoted its ecological separation from its parental species and facilitated its successful colonization and establishment in high-altitude habitats. [ABSTRACT FROM AUTHOR]

• The stomata of angiosperms respond to changes in ambient atmospheric concentrations of CO2 ( Ca) in ways that appear to optimize water-use efficiency. It is unknown where in the history of land plants this important stomatal control mechanism evolved. Here, we test the hypothesis that major clades of plants have distinct stomatal sensitivities to Ca reflecting a relatively recent evolution of water-use optimization in derived angiosperms. • Responses of stomatal conductance ( gs) to step changes between elevated, ambient and low Ca (600, 380 and 100 µmol mol−1, respectively) were compared in a phylogenetically and ecologically diverse range of higher angiosperms, conifers, ferns and lycopods. • All species responded to low Ca by increasing gs but only angiosperm stomata demonstrated a significant closing response when Ca was elevated to 600 µmol mol−1. As a result, angiosperms showed significantly greater increases in water-use efficiency under elevated Ca than the other lineages. • The data suggest that the angiosperms have mechanisms for detecting and responding to increases in Ca that are absent from earlier diverging lineages, and these mechanisms impart a greater capacity to optimize water-use efficiency. [ABSTRACT FROM AUTHOR]

This paper reports the influence of the osmotic adjustment capacity and turgor potential (TP) on tolerance to drought in 12 cultivated genotypes, six breeding lines and six cultivars of barley ( Hordeum vulgare L.) under terminal water-stress conditions. When the crops reached the flag leaf stage, half of the experimental plots in which they were grown were submitted to water stress treatment and the remainder maintained under optimal irrigation conditions. Differences were seen in the osmotic adjustment, relative water content (RWC) and water potential (WP) of the different genotypes. Two of the breeding lines showed the greatest osmotic adjustment capacities, maintaining their TPs better than the other genotypes studied. A positive, significant correlation was found between yield and osmotic adjustment capacity, RWC and WP under water-stress conditions. Osmotic adjustment capacity and TP were linearly related, indicating that as water stress increases osmotic adjustment favours the maintenance of higher TPs. Significant correlations were found between osmotic adjustment capacity and grain filling rate and grain yield. Under conditions of terminal water stress, yield was negatively correlated with the number of days to ear emergence; no correlation was found between osmotic adjustment capacity and earliness. Early ear emergence, a good osmotic adjustment capacity and high RWC values all contributed to yield increases under terminal water-stress conditions. [ABSTRACT FROM AUTHOR]

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.

A greenhouse experiment was performed in order to investigate the effects of different levels of water stress on leaf water potential (Ψw), stomatal resistance (rs), protein content and chlorophyll (Chl) content of tomato plants ( Lycopersicon esculentum Mill. cv. Nikita). Water stress was induced by adding polyethylene glycol (PEG 6 000) to the nutrient solution to reduce the osmotic potential (Ψs). We investigated the behavior of anti-oxidant enzymes, such as catalase (CAT) and superoxide dismutase (SOD), during the development of water stress. Moderate and severe water stress (i.e. Ψs= -0.51 and -1.22 MPa, respectively) caused a decrease in Ψw for all treated (water-stressed) plants compared with control plants, with the reduction being more pronounced for severely stressed plants. In addition, rs was significantly affected by the induced water stress and a decrease in leaf soluble proteins and Chl content was observed. Whereas CAT activity remained constant, SOD activity was increased in water-stressed plants compared with unstressed plants. These results indicate the possible role of SOD as an anti-oxidant protector system for plants under water stress conditions. Moreover, it suggests the possibility of using this enzyme as an additional screening criterion for detecting water stress in plants. (Managing editor: Ping He) [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]

We examined the stomatal response to leaf excision in an evergreen woody shrub, Photinia × fraseri, using a novel combination of gas exchange, traditional water relations and modelling. Plants were kept outdoors in mild winter conditions (average daily temperature range: −1 to 12 °C) before being transferred to a glasshouse (temperature range: 20–30 °C) and allowed to acclimate for different periods before experiments. ‘Glasshouse plants’ were acclimated for at least 9 d, and ‘outdoor plants’ were acclimated for fewer than 3 d before laboratory gas exchange experiments. The transient stomatal opening response to leaf excision was roughly twice as long in outdoor plants as in glasshouse plants. To elucidate the reason for this difference, we inferred variables of stomatal water relations (epidermal and guard cell turgor pressures and guard cell osmotic pressure: Pe, Pg and πg, respectively) from stomatal conductance ( gs) and bulk leaf water potential ( ψl), using a hydromechanical model of gs. ψl was calculated from cumulative post-excision transpirational water loss using empirical relationships between ψl and relative water content obtained on similar leaves. Inferred Pg and Pe both declined immediately after leaf excision. Inferred πg also declined after a lag period. The kinetics of πg adjustment after the lag were similar in outdoors and glasshouse plants, but the lag period was much longer in outdoor plants. This suggests that the longer transient opening response in outdoor plants resulted from slower induction, not slower execution, of guard cell osmoregulation. We discuss the implications of our results for the mechanism of short-term stomatal responses to hydraulic perturbations, for dynamic modelling of gs and for leaf water status regulation. [ABSTRACT FROM AUTHOR]

Vitis vinifera L. berries are non-climacteric fruits that exhibit a double-sigmoid growth pattern, and at the point known as ‘veraison’, which is just before the beginning of the second period of rapid fruit growth, these berries undergo several abrupt physiological changes. Cell pressure probe was used to examine the in situ turgor (P) of cells in the mesocarp during berry development and in response to plant water deficits. Initial tests comparing attached and detached berries demonstrated that cell P was stable for up to 48 h after detachment from the vine, provided that water loss from the berry was prevented. Cell P at pre-dawn was on the order of 0.25 MPa pre-veraison (PreV) and was reduced by an order of magnitude to 0.02 MPa post veraison (PostV). Cell P declined slightly but significantly with depth from the berry surface PreV, but not PostV. When water was withheld from potted vines, cell P declined about 0.2 Mpa, as pre-dawn vine water potential declined about 0.6 MPa over 12 d, whereas cell P was completely insensitive to a 1.10 MPa decrease in pre-dawn vine water potential after veraison. Rewatering of stressed plants also resulted in a 24 h recovery of cell P before, but not after veraison. The substantial decline in cell P around veraison is consistent with the decline in berry firmness that is known to occur at this time, and the PostV insensitivity of P to changes in vine water status is consistent with current hypotheses that the PostV berry is hydraulically isolated from the vine. The fact that a measurable P of about 0.02 MPa and typical cell hydraulic/osmotic behaviour were exhibited in PostV berries, however, indicates that cell membranes remain intact after veraison, contrary to many current hypotheses that veraison is associated with a general loss of membrane function and cellular compartmentation in the grape berry. We hypothesize that cell P is low in the PostV berry, and possibly other fleshy fruits, because of the presence of regulated quantities of apoplastic solutes. [ABSTRACT FROM AUTHOR]

Red-osier dogwood (Cornus stolonifera Michx, Syn. Cornus sericea), a species relatively well adapted to moderately saline conditions compared with other boreal species, was used to test the effects of NaCl on plant water relations, cell wall elasticity, and cell wall composition of seedlings. Three month-old seedlings were treated hydroponically with 0, 25, and 50 mM NaCl for 21 days. The osmotic potential at full turgor, osmotic potential at turgor loss, pressure potential at full turgor, and relative water content at turgor loss of red-osier dogwood shoot tissue were not significantly affected by the NaCl treatments. Cell wall elasticity of the shoot tissues did not change following NaCl treatments, suggesting that elastic adjustment did not play a role in the adaptation mechanism. Hemicellulose content of the cell wall increased in salt treated seedlings. The primary sugar found in the cell wall hemicellulose fraction was xylose. In the pectin fraction arabinose and galacturonic acid were the main sugars. Sodium chloride stress did not alter the sugar composition of the hemicellulose fraction; however, NaCl did increase the amount of rhamnose in the pectin fraction. The results of this study suggest that at moderate salinity red-osier dogwood does not make any osmotic or elastic adjustments in the shoot tissue, but some changes in the cell wall composition do occur. These changes could contribute to the decrease in growth recorded in red-osier dogwood during NaCl stress. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigated the possibility that abscisic acid (ABA) and cytokinins may mediate the effect of water deficit that enhances plant senescence and remobilization of pre-stored carbon reserves. Two high lodging-resistant wheat (Triticum aestivum L.) cultivars were field grown and treated with either a normal or high amount of nitrogen at heading. Well-watered (WW) and water-stressed (WS) treatments were imposed from 9 d post-anthesis until maturity. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress facilitated the reduction of non-structural carbohydrate in the stems and promoted the re-allocation of prefixed [sup 14] C from the stems to grains, shortened the grain filling period and increased the grain filling rate. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the stems and leaves. ABA correlated significantly and negatively, whereas Z + ZR correlated positively, with Pr and Chl of the flag leaves. ABA but not Z + ZR, was positively and significantly correlated with remobilization of pre-stored carbon and grain filling rate. Exogenous ABA reduced Chl in the flag leaves, enhanced the remobilization, and increased grain filling rate. Spraying with kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigated aerenchyma formation and function in adventitious roots of wheat (Triticum aestivum L.) when only a part of the root system was exposed to O[sub 2] deficiency. Two experimental systems were used: (1) plants in soil waterlogged at 200 mm below the surface; or (2) a nutrient solution system with only the apical region of a single root exposed to deoxygenated stagnant agar solution with the remainder of the root system in aerated nutrient solution. Porosity increased two- to three-fold along the entire length of the adventitious roots that grew into the water-saturated zone 200 mm below the soil surface, and also increased in roots that grew in the aerobic soil above the water-saturated zone. Likewise, adventitious roots with only the tips growing into deoxygenated stagnant agar solution developed aerenchyma along the entire main axis. Measurements of radial O[sub 2] loss (ROL), taken using root-sleeving O[sub 2] electrodes, showed this aerenchyma was functional in conducting O[sub 2.] The ROL measured near tips of intact roots in deoxygenated stagnant agar solution, while the basal part of the root remained in aerated solution, was sustained when the atmosphere around the shoot was replaced by N[sub 2] . This illustrates the importance of O[sub 2] diffusion into the basal regions of roots within an aerobic zone, and the subsequent longitudinal movement of O[sub 2] within the aerenchyma, to supply O[sub 2] to the tip growing in an O[sub 2] deficient zone. [ABSTRACT FROM AUTHOR]

Evaluates dry matter (DM) production of orchardgrass and perennial ryegrass at give irrigation levels. Line-source irrigation; Relative differences of species for DM production; Variation of responsiveness of ryegrass-hybrid to changing water levels.

Studies the trends and stability in forage yield across water levels by tall fescue cultivars of Festuca arundinacea. Analysis of dry matter yield for three growing seasons; High dry matter in early summer; High dry matter production by cultivars infected with the endophytic fungus Neotyphodium coenophialum.

Discusses the response of bog and fen plant communities to warming and water-table manipulations. Comparison of primary productivity (PP) of bog and fen to wet treatment; Decline of PP with increasing water depth; Diversity of species productivity.

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]

The water content‐water potential relation in stressed and unstressed cassava (Man‐ihot species) was examined to ascertain (i) the magnitude of osmotic adjustment in response to water stress and (ii) the mechanisms of such adjustments. Water stress resulted in a displacement of the water content‐potential relation such that at any leaf water potential the water content was higher in the stressed plants. The osmotic potentials of turgid leaves (100% relative water content) were ‐0.97 and ‐1.00 MPa in the unstressed cultivars CMC 9 and MCOL 113 respectively. In the stressed plants, the values were‐1.13 MPa (CMC 9) and‐1.14 MPa (MCOL 113). The 0.14 to 0.16 MPa osmotic potential difference between the stressed and unstressed plants suggests that a stress‐induced osmotic adjustment occurred in both cultivars. The biiSk volumetric elastic moduli at turgor pressures above 0.10 MPa were 9.84 MPa (CMC 9) and 13.58 MPa (MCOL 113) in the unstressed plants. Tbe higher values found in the stressed plants, 14.56 MPa in CMC 9 and 16.91 MPa in MCOL 113, suggest a stress‐induced decrease in cell wall elasticity. Hence, the observed shift in the wafer content‐potential relations in the cassava involved both an osmotic adjustment and a decrease in cell wall elasticity. Increasing the number of stress cycles per plant did not cause a further displacement of the water content‐potential curves. [ABSTRACT FROM AUTHOR]

Measures of leaf tissue elasticity were determined by analyzing the turgor pressure-water content relation developed from pressure-volume experiments in four naturally occurring forest tree species. The relation between the bulk tissue elastic modulus and tissue turgor pressure varied by spades and varied with state of leaf maturation through the growing season. Although the values of the elastic modulus reported here agree in magnitude with values reported in general for higher plant tissue, the functional dependency of the apparent elasticity on tissue water status was more complex in this study than can be accounted for by current models. [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]

The kinetics of growth and georeaction of horizontal or vertical maize (cv. ORLA 264) apical root segments were analysed. Elongation and curvature data were fitted to a mathematical function and the effect of both light and decapitation reported. Elongation of horizontal segments was found to be more sensitive to light than to decapitation. A light treatment or the decapitation presented several effects on the shape of the growth curves. Growth of vertical segments was affected much more by decapitation than by light treatment. The shape of the curves was clearly different for decapitated and intact segments. Curvature is affected both by light and decapitation but the shape of the bending curves is modified principally by decapitation. Under the present conditions used, growth and georeaction of root segments do not seem to be strictly correlated. [ABSTRACT FROM AUTHOR]

The pith parenchyma in tomato (Lycopersicum esculentum) stems was found to be disrupted in response to water stress (stem pithiness). The process of the degradation starts at the upper part of the stem and proceeds downwards as the stress is prolonged. The damage to the stem tissue was found to be irreversible upon rehydration of the stressed plants. Scanning electron microscopy revealed that the protoplast of the affected cells is disrupted first, followed by degradation of the cell wall. Application of abscisic acid (ABA) induced pithiness in non‐stressed plants and also enhanced the effect of a short period of dehydration. Kinetin, although causing severe wilting, did not induce pithiness. However, when given after a short period of water stress or within the period of stress, kinetin enhanced pithiness development. In the course of the stress, ABA levels in the upper part of the stem and in the young leaves were higher than the levels found in the lower parts of the plant shoot. The increase in ABA levels was detected before any sign of pithiness. It is suggested that ABA might be the triggering agent of the cellular degradation process initiated by 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]

42K and 14C (U)-glucose uptake by foliar discs of maize (Zea mays L.) and pelargonium (Pelargonium zonale L.) is inhibited by dimethyl sulfoxide (DMSO) at concentrations of 5 and 10%. This effect increases with the duration of the absorption and appears with varied concentrations in K or glucose. In most cases, this inhibitory effect is less with aged discs than with freshly cut discs. Besides, the DMSO (10%) enhances the exsorption of 42K by foliar discs of maize. The effects of DMSO and two osmotic agents, mannitol and polyethylene glycol 1000, on the uptake and water content of discs arc compared. It seems that the effect of DMSO on the uptake is not only an osmotic effect it may also he related to other actions of this substance in affecting an active uptake. [ABSTRACT FROM AUTHOR]

Waterlogging the soil promotes epinastic growth of tomato petioles and increases the concentration of ethylene which can be extracted from various parts of the shoot. These concentrations exceed those normally required to promote epinasty when applied to the shoots of non-waterlogged plants. Waterlogging also results in a rapid decline in the concentration of dissolved oxygen in the soil water. Low concentrations of oxygen around the roots of plants growing in nutrient solution promote epinastic growth and also increase ethylene concentration in the leaves. Experiments with detached shoots indicate that the root system is required for the response to low O[SUB2] concentrations to develop. Ethylene concentrations in the soil can increase during waterlogging to levels which may allow sufficient movement into the shoot to stimulate epinasty. Treatment with substances which can inhibit the action of ethylene, such as carbon dioxide or 7-chloro-4-ethoxycarbonylmethoxy-5-methyl-2, 1, 3-benzothiadiazole also inhibit the epinastic response in waterlogged plants, in plants with low O[SUB2] concentrations around the roots and in plants treated with ethylene. The internal level of carbon dioxide in the lower leaves is little affected by waterlogging for up to 96 h. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa[L.] cv. IR‐72) was grown for a season in sunlit, controlled‐environment chambers at 350 or 700 µmol CO2 mol−1 under continuously flooded (unstressed) or drought‐imposed periods at panicle initiation (stressed). The midday canopy photosynthetic rates (Pn), measured at the CO2 concentration ([CO2]) used for growth, were enhanced by high [CO2] but reduced by drought. High [CO2] increased Pn by 18 to 34% for the unstressed plants, and 6 to 12% for the stressed plants. In the unstressed plants, CO2 enrichment increased water‐use efficiency (WUE) by 26%, and reduced evapotranspiration (ET) by 8 to 14%. Both high [CO2] and severe drought decreased the activity and content of ribulose bisphosphate carboxylase‐oxygenase (Rubisco). High‐CO2‐unstressed plants had 6 to 22% smaller content and 5 to 25%, lower activity of Rubisco than ambient‐CO2‐unstressed plants. Under severe drought, reductions of Rubisco were 53 and 27% in activity and 40 and 12% in content, respectively, for ambient‐ and high‐CO2 treatments. The apparent catalytic turnover rate (Kcat) of midday fully activated Rubisco was not altered by high [CO2], but severe drought reduced Kcat by 17 to 23%. Chloroplasts of the high‐CO2 leaves contained more, and larger starch grains than those of the ambient CO2 leaves. High [CO2] did not affect the leaf sucrose content of unstressed plants. In contrast, severe drought reduced the leaf starch and increased the sucrose content in both CO2 treatments. The activity of leaf sucrose phosphate synthase of unstressed plants was not affected by high [CO2], whereas that of ambient‐CO2‐grown plants was reduced 45% by severe drought. Reduction in ET and enhancements in both Pn and WUE for rice grown under high [CO2] helped to delay the adverse effects of severe drought and allowed the stressed plants to assimilate CO2 for an extra day. Thus, rice grown in the next century may utilize less water, use water more efficiently, and be able to tolerate drought better under some situations. [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]

Examines the factors affecting the foliage and growth of river red gum Eucalyptus camaldulensis in New South Wales. Insect herbivory; Moisture stress; Distance from intermittently flooded waterways; Xylem water pressure potential; Mean leaf area.

When plants of Lolium perenne were subjected to one cycle of soil drying, to repeated cycles of drying, or when they were grown in dry soils, the relative growth rate of the root system was reduced more than that of the shoot system. This brought about a decrease in the root:shoot ratio. Drought initially resulted in lower availability of water near to the soil surface than at greater depths. Consequently, growth of that part of the root system near the soil surface was restricted, and newly initiated main roots at the base of the shoot were unable to elongate. When plants were grown in solution of low osmotic potential, there was no effect on distribution of dry matter between roots and shoots, except at the lowest potential (−9·5 bars) which reduced root growth rather more than shoot growth. The effect of drought on root:shoot ratio in these experiments is compared with that reported by others. It is suggested that, in some circumstances, the availability of phosphate in the soil may influence the effect of drought on root:shoot ratios. [ABSTRACT FROM AUTHOR]

Valencia orange trees were subjected to water stress, under field conditions at Tacna, Arizona, inducing leaf water potentials between −1 and −6.6 Mpa before dawn. The water status of trees was then studied after irrigation. Rehydration began immediately after irrigation, and leaf water potentials reached normal values in less than a week. The stomatal conductance of leaves recovered much more slowly, the time being related directly to leaf water potential prior to irrigation. The stomatal conductance of trees which had leaf water potential s of less than −5 Mpa before dawn, prior to irrigation, did not fully recover in 2 months. Leaves that had undergone severe water stress h ad lower leaf water potentials, for a given relative water content, than unstressed leaves. These differences are discussed in terms of osmotic adjustment and changes in bound water. [ABSTRACT FROM AUTHOR]

This study on expansive growth of the first leaf of maize has two goals: one is to determine how the sensitivity of growth to changes in water status varies with the initial water status of the leaf, and the other is to adapt the pressure-jump technique of Okamoto et al. (1989, Plant and Cell Physiology 30, 979–985), developed for studying growth of excised stem segments, for use on whole seedlings. Initial water status was varied by using: transpiring vs. non-transpiring conditions, seedlings differing in emerged leaf length and hence transpiring area, and root medium without mannitol vs. medium with added mannitol (to –0·3 MPa). The results show that growth changed with changes in plant water status when the water status was low, but was unaffected when water status was very high. A stepwise change in hydrostatic pressure on the root medium was quickly and fully transmitted to the base of the leaf. The increase in leaf elongation due to a pressure step of 0·025 MPa was negligible under conditions of high plant water status and became substantial under conditions of low water status. In adapting the pressure-jump method to the whole seedling, there was some loss of resolution, and the yield threshold Y of the Lockhart equation could not be estimated directly. Nonetheless, the data were suitable for the calculation of volumetric extensibility m and the estimation of growth effective turgor (turgor above Y). Extensibility was shown to increase 3- to 4-fold when leaf water status was reduced from the maximum to the point where elongation rate was halved, while growth effective turgor was calculated to diminish even more markedly. [ABSTRACT FROM AUTHOR]

Examines the effects of water-level fluctuations on weekly wetland tree growth in a Southeastern States swamp. Selection of species and study sites; Parameter estimates for water level changes; Effects of changes in atmospheric water balance; Cross-correlations between water-level and tree-growth changes.

The levels of particular mRNA in tomato leaves are altered in response to water stress. Certain transcripts appear as a consequence of the stress whereas others diminish in abundance. These changes were analysed by cell-free translation of leaf RNA followed by two-dimensional polyacrylamide gel electrophoresis of the transition products. Within 20 min of the onset of reduced leaf water potential in detached leaflets, stress-induced mRNAs appear in the transcript population. Other mRNAs accumulate more slowly and include among their in vitro translation products a prominently labelled group of polypeptides of about 18-19 kD. These transcripts are recovered from detached leaflets incubated for 2 and 8h at low water potential and from leaflets of intact plants that were stressed in situ for 10d. An additional water stress-induced mRNA that encodes a 64-kD polypeptide is detected in the transcript population from detached leaflets when [³H]glycine is used in place of [35S]methionine in the cell-free translations. Among the transcripts that decline in abudance as a consequence of water stress is an mRNA that encodes the small subunit of ribulose-1,5-bisphosphate carboxylase. Within 2h of rewatering stressed plants, certain mRNAs that were lost from the population return and those in the 18-19 kD range that are associated with the stress are not detectable. [ABSTRACT FROM AUTHOR]

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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]

Two rapid methods of assessing relative turgidity in maize are described. The first involved measuring the water uptake by discs of leaf tissue but omits the oven dry weight from the calculation. Where the position on the leaf was standardized, the relationship was linear (r = 0.99***) over a wider range than normally encountered in field conditions. The regression relationship held for plants grown under a wide variety of environmental conditions and at various stages of development. The second method utilized a series of photographic standards of plants at different relative turgidities. Relative turgidity could then be estimated visually by comparing the plant and the photographic standards. Accuracy with either method was similar to the experimental error of relative turgidity measured by normal means. Both offer a considerable saving in time, especially the photographic standard method which allows instantaneous readings to be made. This should permit field workers to assess rapidly the water status of their crop without the labour involved in conventional measurements. [ABSTRACT FROM AUTHOR]