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Drought limits the growth and development of Phaseolus vulgaris L. (known as common bean). Common bean plants contain various phenylpropanoids, but it is not known whether the levels of these metabolites are altered by drought. Here, BT6 and BT44, two white bean recombinant inbred lines (RILs), were cultivated under severe drought. Their respective growth and phenylpropanoid profiles were compared to those of well-irrigated plants. Both RILs accumulated much less biomass in their vegetative parts with severe drought, which was associated with more phaseollin and phaseollinisoflavan in their roots relative to well-irrigated plants. A sustained accumulation of coumestrol was evident in BT44 roots with drought. Transient alterations in the leaf profiles of various phenolic acids occurred in drought-stressed BT6 and BT44 plants, including the respective accumulation of two separate caftaric acid isomers and coutaric acid (isomer 1) relative to well-irrigated plants. A sustained rise in fertaric acid was observed in BT44 with drought stress, whereas the greater amount relative to well-watered plants was transient in BT6. Apart from kaempferol diglucoside (isomer 2), the concentrations of most leaf flavonol glycosides were not altered with drought. Overall, fine tuning of leaf and root phenylpropanoid profiles occurs in white bean plants subjected to severe drought. [ABSTRACT FROM AUTHOR]

Water-use efficiency (WUE) may be a useful trait for improving productivity of cotton (Gossypium spp.) under certain water-limited conditions, but it is difficult to measure in the field or in large controlled-environment screening studies. Recently, an easily measured trait, the epidermal conductance of dark-adapted leaves ([g.sub.dark]), was shown to be predictive of whole-plant WUE in soybean [Glycine max (L.) Merr.]. Here, a greenhouse experiment was conducted using 22 cotton race stocks, converted lines, and commercial varieties to determine if the relationship between WUE and [g.sub.dark] previously observed in soybean also exists in cotton. A secondary objective was to determine if genotypic differences in WUE and [g.sub.dark] in cotton were constitutive in nature, or if they differed between water replete and drought conditions. There was significant genotypic variation for both WUE and [g.sub.dark], and in both cases the lack of a treatment x genotype interaction indicated that the trait was constitutive. The relationship between WUE and [g.sub.dark] (r = -0.7,5, P < 0.0001) was very similar to that reported previously for soybean. Understanding the mechanistic link between [g.sub.dark] and WUE may provide further insight into the physiological basis of genotypic differences in WUE.

Three physiological traits that may affect performance of soybean [Glycine max (L.) Merr.] when soil water availability is limiting are (i) water use efficiency (WUE), (ii) regulation of whole plant water use in response to soil water content, and (iii) leaf epidermal conductance ([g.sub.e]) when stomata are closed. Six soybean plant introductions (PIs), eight breeding lines derived from them, and nine cultivars were compared for variability in these three traits during vegetative growth in two greenhouse studies. In the first experiment, whole plant water use, normalized both to plant size and evaporative demand (the normalized transpiration ratio, NTR), was monitored during a 10-d cycle of gradually increasing drought stress and then for an additional 2 d following rewatering. The critical soil water content at which each plant began to reduce its water use (FFS[W.sub.c]), was determined. The WUE was estimated as the ratio of total plant dry weight to total water used. In the second experiment, [g.sub.e] was determined for these same 23 genotypes by measuring leaf water vapor exchange after a 36-h dark adaptation. Substantial variation was found among genotypes for WUE, FFS[W.sub.c], [g.sub.e], and also the extent to which NTR recovered on rewatering. Generally, adapted cultivars had greater WUE and lower [g.sub.e] than did PIs. However, PI 471938 and its progeny N98-7264 were clear exceptions to this trend. An unexpected finding was that WUE was significantly negatively correlated with [g.sub.e] across genotypes.

Water stress may reduce leaf net photosynthetic carbon assimilation (AN) through both stomatal effects, which reduce the leaf internal C[O.sub.2] concentration ([C.sub.i]), and nonstomatal effects, which result in reduced [A.sub.N] at a given level of [C.sub.i]. However, the leaf gas exchange techniques used to calculate [C.sub.i] are susceptible to important artifacts when applied to water-stressed leaves, making such [C.sub.i] estimates unreliable. As an alternative to [C.sub.i], the C[O.sub.2] concentration in the chloroplast ([C.sub.C]) can be calculated from simultaneous measurements of [A.sub.N] from gas exchange measurements, and the thylakoid electron flux from chlorophyll fluorometry. This permits diffusional effects (stomatal plus mesophyll limitations to C[O.sub.2] diffusion) to be differentiated from chloroplast-level effects. We used this method to investigate physiological restrictions to photosynthesis in leaves of water stressed cotton (Gossypium hirsutum L.) plants in a series of greenhouse experiments. A null-balance lysimeter was used to slowly induce four distinct levels of water stress. Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments more effectively than gas exchange measurements alone. All treatments reduced [C.sub.C], but only the two most severe stress treatments significantly increased nondiffusional restrictions, detectable as a reduction in the slope of [A.sub.N] on [C.sub.C]. In a second experiment, recovery of leaf photosynthesis was determined 24 and 48 h after relief of a severe stress by rewatering. Recovery of the [A.sub.N]/[C.sub.C] relationship was substantial but incomplete after 24 h and did not recover further by 48 h after rewatering, indicating lasting chloroplast-level injury as a result of the stress. Similar experiments should be conducted under field conditions to determine if water stress results in irreversible chloroplast-level injury in field-grown cotton. Abbreviations: α, leaf fractional absorption of incident PPFD; [A.sub.N], leaf net C[O.sub.2] assimilation rate; [A.sub.G], leaf gross C[O.sub.2] assimilation rate; [A.sub.N-C], leaf net C[O.sub.2] assimilation rate corrected for sample chamber leakage; [A.sub.N-M], measured leaf net C[O.sub.2] assimilation rate (uncorrected for sample chamber leakage); [C.sub.A], ambient C[O.sub.2] concentration; [C.sub.C], C[O.sub.2] concentration at the carboxylation site in the chloroplast; [C.sub.i], leaf internal C[O.sub.2] concentration; [C.sub.S], C[O.sub.2] concentration in the sample chamber; DAP, days after planting; [Φ.sub.II], quantum efficiency of Photosystem II; [f.sub.II], fraction of absorbed PPFD absorbed by the antennae of Photosystem II; [F.sub.S], steady state chlorophyll fluorescence signal; [F'.sub.M], maximum (light saturated) chlorophyll fluorescence signal; [G.sub.L], sample chamber conductance to C[O.sub.2] flux (leakage); [G.sub.M], mesophyll conductance to C[O.sub.2] in the liquid phase;[ G.sub.S], stomatal conductance to water vapor; IRGA, infrared gas analyzer; [J.sub.e], electron flux through Photosystem II; [K.sub.S], C[O.sub.2]/[O.sub.2] specificity ratio of RubisCO; L, leaf area in the sample chamber; LRWC, leaf relative water content; [O.sub.C] oxygen concentration at the carboxylation site in the chloroplast; PPFD, photosynthetic photon flux density; [R.sub.D], rate of leaf respiration in the dark; RSWC, relative soil water content; [v.sub.C], velocity of the carboxylation reaction of RubisCO: [v.sub.O], velocity of the oxygenation reaction of RubisCO; [W.sub.D], pot plus soil dry weight; [W.sub.P], plant fresh weight; [W.sub.S], pot plus soil water saturated weight; [W.sub.T], pot target weight., SOIL WATER DEFICITS constitute a primary limitation to crop productivity in many regions of the world. An enhanced mechanistic understanding of how water stress affects crop growth could benefit current [...]

Many different approaches have been used for the simulation of drought stress in pot studies. An ideal technique should (i) maintain uniform soil water content within the rooting zone, (it) allow the rate at which stress develops to be precisely controlled, regardless of differences in plant size or variations in environmental conditions, (iii) permit a range of physiologically distinct stress levels to be imposed and maintained indefinitely, and (iv) provide a means of accurately quantifying the stress level. In the present study, a computer automated null-balance lysimeter was evaluated against these criteria. Separate experiments were conducted with soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) growing in 2.5-L pots. Single plant water use was quantified gravimetrically by frequent, automated recording of pot weights, and transpired water was replaced by a computer controlled watering system such that relative soil water content (RSWC) was maintained within a narrow range. In this way, pots were held at four RSWC levels ranging from 20 to 75%. Despite the frequent additions of small amounts of water at the tops of the pots, soil water distribution within the pots was found to be remarkably uniform, suggesting that bulk RSWC was a suitable indicator of the soil water deficit experienced by the roots. Measurements of whole plant water use indicated that the four RSWC levels represented four statistically distinct levels of water stress. It is concluded that null balance lysimetry is a useful approach to simulating drought stress in greenhouse experiments, with specific advantages over other available techniques., MEASUREMENTS OF PLANT responses to soil water deficits are often performed under greenhouse or other controlled-environment conditions. Such studies may be undertaken to characterize fundamental physiological responses of plants to [...]

Aims: In Ontario, Canada, acreage of red clover (Trifolium pratense L.) intercropped with winter wheat (Triticum aestivum L. em. Thell) has declined, despite well-documented soil and yield benefits. The decline has resulted from increasing prevalence of stand non-uniformity, which has been attributed in part to soil moisture deficits. We examined whether there are genotypic differences in drought response between red clover varieties.Methods: A double-cut (Belle) and a single-cut variety (Altaswede) were grown under four different durations of drought (4, 8, 12 and 16 days below 15% relative soil water content, RSWC). Shoot dry weight, shoot relative water content (RWC), leaf area and crown water content were measured in control, drought and drought + recovery treatments.Results: Belle used significantly more water during soil moisture deficit and had greater leaf area, shoot dry weight and RWC compared to Altaswede. In contrast, Altaswede had significantly higher survival rates than Belle, attributed to maintenance of meristematic tissue viability in the crown where re-growth, after shoot tissue desiccation, can occur.Conclusions: By demonstrating genotypic variation in survival strategies of red clover, traits can be identified for the development of improved varieties. Varieties with higher survival rates during drought will result in more uniform stands and increased utilization of red clover for environmental and yield benefits. [ABSTRACT FROM AUTHOR]

Germination and seedling establishment are the major and critical steps in establishment of the crops in the arid and semi-arid environments. In this study an experiment was conducted to evaluate the effects of different time seed priming (osmo-hydropriming) on germination and seedling growth of Secale montanume seeds under drought conditions. Seeds were immersed in water with osmotic potentials of -0.5, -1 and -1.5 MPa. PEG600 was employed to induce the required levels of osmotic potentials. Induction of hydropriming was obtained by immersing the seeds in distilled water with aeration and no aeration conditions. Both two priming treatments were conducted at 3 time duration (6, 12 and 24 hours). These primed seeds were germinated and grew at osmotic potentials of 0 (distilled water), -0.5, -1, and -1.5 MPa by PEG6000. Results showed that the seed germination and seed growth were inhibited by increasing drought stress as the germination percentage of hydroprimed seeds with aeration was reduced from 74.02% to 60.45%. Both shoot and root growths were inhibited by increasing osmotic potential. Hydroprimed seeds with aeration caused reduction shoot and root length, while root/shoot length ratio was increased by hydroprimng without aeration. The least priming time (6 hr) had more effects on germination percentage. Result also showed that seed treatment at difference levels of PEG significantly affected germination characteristics. The highest germination percentage was obtained from seed priming with PEG induced -0.5 MPa osmotic potential. The highest root/shoot length ratio was related to osmopriming with -0.5 MPa. The time of osmopriming didn't show significant effect on germination characters and seedling growth. However 6 h osmopriming was more effective. [ABSTRACT FROM AUTHOR]