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Summary: Clarifying the coordination of leaf hydraulic traits with gas exchange across closely‐related species adapted to varying rainfall can provide insights into plant habitat distribution and drought adaptation.The leaf hydraulic conductance (Kleaf), stomatal conductance (gs), net assimilation (A), vein embolism and abscisic acid (ABA) concentration during dehydration were quantified, as well as pressure–volume curve traits and vein anatomy in 10 Caragana species adapted to a range of mean annual precipitation (MAP) conditions and growing in a common garden.We found a positive correlation between Ψleaf at 50% loss of Kleaf (KleafP50) and maximum Kleaf (Kleaf‐max) across species. Species from low‐MAP environments exhibited more negative KleafP50 and turgor loss point, and higher Kleaf‐max and leaf‐specific capacity at full turgor, along with higher vein density and midrib xylem per leaf area, and a higher ratio of Kleaf‐max : maximum gs. Tighter stomatal control mediated by higher ABA accumulation during dehydration in these species resulted in an increase in hydraulic safety and intrinsic water use efficiency (WUEi) during drought.Our results suggest that high hydraulic safety and efficiency combined with greater stomatal sensitivity triggered by ABA production and leading to greater WUEi provides drought tolerance in Caragana species adapted to low‐MAP environments. [ABSTRACT FROM AUTHOR]

Caragana species are widespread in northwest China. However, species in semiarid areas of Inner Mongolia experience summer and autumn rainfall, whereas morphologically similar close relatives in arid areas in Xinjiang Province experience wet springs, but hot dry summers. We hypothesize that the differences among species in response to soil drought help to explain their distributions. A comparison of the closely related species C. intermedia and C. microphylla from Inner Mongolia (semiarid species) and C. pruinosa and C . spinosa from Xinjiang (arid species) was conducted to examine whether responses to a water deficit in a pot experiment were associated with the environments of their habitat. In the two semiarid species, the stomatal conductance was relatively insensitive to the decrease in predawn leaf water potential (Ψ), and leaves did not abscise or die even when the Ψ decreased below −6.0 MPa, while in seedlings of the two arid species the stomata closed at a relatively high Ψ, and the leaves abscised gradually when Ψ fell below about −3.0 MPa. Furthermore, major vein density, minor vein density and the cubed ratio of the conduit wall thickness to the conduit lumen breadth [(t/b)] of minor veins increased by an average of 60, 150 and 220 %, respectively, in the semiarid species compared with the arid species. The results indicated that semiarid species have typical anisohydric properties, while arid species have typical isohydric properties. We suggest that the divergence in water-use strategies in the genus may be associated with variation in vein architecture, and may possibly play an important role in determining the distribution of these species in the different environments of northwest China. [ABSTRACT FROM AUTHOR]

γ-aminobutyric acid (GABA) is a non-protein amino acid involved in various physiological processes; it aids in the protection of plants against abiotic stresses, such as drought, heavy metals, and salinity. GABA tends to have a protective effect against drought stress in plants by increasing osmolytes and leaf turgor and reducing oxidative damage via antioxidant regulation. Guard cell GABA production is essential, as it may provide the benefits of reducing stomatal opening and transpiration and controlling the release of tonoplast-localized anion transporter, thus resulting in increased water-use efficiency and drought tolerance. We summarized a number of scientific reports on the role and mechanism of GABA-induced drought tolerance in plants. We also discussed existing insights regarding GABA's metabolic and signaling functions used to increase plant tolerance to drought stress. [ABSTRACT FROM AUTHOR]

In recent years, research on spermine (Spm) has turned up a lot of new information about this essential polyamine, especially as it is able to counteract damage from abiotic stresses. Spm has been shown to protect plants from a variety of environmental insults, but whether it can prevent the adverse effects of drought has not yet been reported. Drought stress increases endogenous Spm in plants and exogenous application of Spm improves the plants' ability to tolerate drought stress. Spm's role in enhancing antioxidant defense mechanisms, glyoxalase systems, methylglyoxal (MG) detoxification, and creating tolerance for drought-induced oxidative stress is well documented in plants. However, the influences of enzyme activity and osmoregulation on Spm biosynthesis and metabolism are variable. Spm interacts with other molecules like nitric oxide (NO) and phytohormones such as abscisic acid, salicylic acid, brassinosteroids, and ethylene, to coordinate the reactions necessary for developing drought tolerance. This review focuses on the role of Spm in plants under severe drought stress. We have proposed models to explain how Spm interacts with existing defense mechanisms in plants to improve drought tolerance. [ABSTRACT FROM AUTHOR]

We evaluated the importance of conserved water use in drought adaptation in soybean [ Glycine max (L.) Merr.], and identified the traits involved in this mechanism. Eight soybean genotypes, four landraces and four recent cultivars, were collected and yield performance in the field was determined and used in pot experiments to evaluate the yield performance and the water use pattern under three soil moisture treatments imposed from 40 days after sowing: well-watered [WW, soil water content (SWC) maintained between 85%–100% field capacity (FC)]; water stress (WS, water withheld until SWC decreased to 30% FC, rewatered to 100% FC and water withheld again to 30% FC); and terminal water stress (TWS, water withheld until maturity). The recent cultivars all out-yielded the landraces in two different years in the field and under well-watered conditions in the pot experiment. Among the eight soybean genotypes, J19 and ZH – two recent cultivars with lower daily water use before flowering, but higher use after flowering – had the best yield performance in the WS and TWS treatments in the pot experiment and in the field. These two soybean genotypes and J19, another recent cultivar, had higher grain yield, hundred-grain weights and water use efficiency for grain yield (WUE G ) in the WS treatments than the other genotypes, and higher hundred grain weights, higher WUE G , higher pod numbers and the only significant grain yield in the TWS treatment. J19 and ZH had low root length densities (RLD), low leaf areas at flowering, and transpiration decreased at high plant available soil water content under drought. Thus, we conclude that reducing RLD and restricting water loss contributed to conserved water use and improved yield performance and WUE G in water-limited conditions. [ABSTRACT FROM AUTHOR]