The Role Of Abscisic Acid In The Regulation Of Root-sourced Signals,Grain Yield And Water Use Efficiency In Spring Wheat

The pot experiments were conducted to investigate the regulation of β-aminobutyric acid (BABA) and exogenous abscisic acid (ABA) addition by soil drenching to root-sourced signals, antioxidant defense, grain yield and water use efficiency for grain (WUEg) in two spring wheat (Triticum aestivum L.) cultivars. The two spring wheat cultivars, Gansu96(GS,1950s) and Longchun8275(LC,1990s), released in different decades and with different yields under drought conditions. Drenching the soil with100μM BABA and10μM exogenous ABA, led to change of ecophysio logical adaptive mechanisms (including root-sourced signals and antioxidant defense) of two spring wheat cultivars during progressive soil drying, and affect their grain yield formation and WUEG under the drought stress.Drenching the soil with100μM BABA increased drought-induced ABA production in leaves, leading to early trigger non-hydraulic root-sourced signals (nHRS) in two spring wheat cultivars. The addition of BABA broadened the soil water content (SWC) threshold range of nHRS in two cultivars to70.7-49.5%FWC for GS (21.2%FWC) and76.9-39.8%FWC for LC (37.1%FWC) compared with62.6-48.5%FWC in GS (14.1%FWC) and69.1-39.4%FWC in LC (29.7%FWC) without BABA addition. Drenching the soil with BABA significantly reduced the lethal water potential (ψ) in two spring wheat (P<0.05), thus increased the desiccation tolerance. In addition, the addition of BABA reduced the reactive oxygen species (ROS)(such as O2-and H2O2), increased the antioxidant enzymes (SOD, CAT, APX and GR) activities, and reduced the malondialdehyde (MDA) levels in leaves at severe water stress levels (50%FWC). Experiment of yield formation showed that addition of BABA did not affect the growth, yield components and grain yield in two spring wheat cultivars under soil drying; and increased WUEg through decreasing water use under moderate water stress (55%FWC). These results indicate that there is a way of effectively priming the preexisting adaptive defense mechanisms to drought stress, in addition to genetic means, to improve the desiccation tolerance and WUEg of wheat.Drenching the soil with10μM exogenous ABA increased the ABA concentration in leaves, reduced stomatal conductance (gs) and the water loss from the leaves and maintained the higher leaf RWC in two spring wheat cultivars during the gradually soil drying. The addition of exogenous ABA significantly reduced the lethal leafψ in two cultivars (P<0.05), thus increased desiccation tolerance. In addition, the addition of exogenous ABA reduced ROS formation, incresed antioxidant enzymens activity and reduced the oxidative damage to lip id membranes (lower concentration of MDA in leaves) at severe water stress (SWC below50%FWC). The effects of exogenous ABA on the lethal leafψ, ROS production and antioxidant enzymes activities in two spring wheat cultivars under soil drying were similar at jointing and booting stages. Exogenous ABA application aggravated the decreases in aboveground growth parameters in two spring wheat caused by moderate water stress (55%FWC), such as plant height, spike per plant and aboveground dry weight, but had no effect on the root dry weight under drought condition, indicating that the shoot was more sensitive to exogenous ABA than root in the two spring wheat. Exogenous ABA application also reduced water use and increased WUEg, but failed to improve the grain yield in the two spring wheat under moderate water stress (55%FWC). These results indicate that ABA plays an important role in reducing water loss, enhancing the antioxidant defense and desiccation tolerance in spring wheat, and improvement of these adaptive mechanisms to drought stress was facilitated to improve WUEq in spring wheat.