Exogenous abscisic acid reduces water loss and improves antioxidant defence, desiccation tolerance and transpiration efficiency in two spring wheat cultivars subjected to a soil water deficit.

The effect of soil drenching with 10µM abscisic acid (ABA) on the physiological responses of two spring wheat (Triticum aestivum L.) cultivars released in different decades was evaluated when subjected to a water deficit at jointing or at booting. Exogenous ABA application increased the ABA concentration in the leaves, reduced the stomatal conductance (gs), slowed the rate of water use, decreased the lethal leaf water potential (ψ) used to measure desiccation tolerance and lowered the soil water content (SWC) at which leaf relative water content (RWC) began to decrease and wilting was observed. Exogenous ABA application also reduced reactive oxygen species (ROS) formation and increased antioxidant enzyme activity, leading to a reduction in the oxidative damage to lipid membranes in both cultivars exposed to water stress at jointing and booting. The decrease in leaf RWC and wilting occurred at lower values of SWC in the recently-released cultivar than in the earlier-released cultivar. The recently-released cultivar also had higher grain yield than the earlier-released cultivar at moderate water stress, but the grain yield in both cultivars was reduced by water stress and by the exogenous ABA treatment. However, exogenous ABA treatment increased transpiration efficiency for grain (TEG) of both cultivars under moderate water stress. These results indicate that ABA played an important role in slowing water use and enhancing the antioxidant defence during soil drying, but this did not result in increased yields under drought stress.