Eco-physiological Adaptive Mechanisms Of Spring Wheat To Drought Stress

Water deficiency is one of the most serious limitations to agricultural productionand crop distribution. It is important to discover crops' eco-physiological adaptivemechanisms to drought, which is beneficial to improve agricultural techniques andcultivate crop varieties in dry land. Spring wheats' eco-physiological adaptation andresponse to drought and production characteristics were investigated by imposition ofprogressive drying. It was concluded that1. In the present study, although cultivated medium (sieved topsoil) was replacedby a peat-perlite mixture, the MRGY was positively correlated with the thresholdrange of nHRS (r=0.99, P＜0.05) and grain yield increased as threshold range ofnHRS increased under moderate water-stress conditions. In addition, grain yield andthe relationship between the MRGY and threshold range of nHRS did notsignificantly differ for varieties under severe water stress. This result indicated thatthe threshold range of nHRS contributed to MRGY and grain yield under mild but notsevere drought.2. In the present study, the MRGY of varieties was positively correlated with OA (r=0.95, P＜0.05) and increased yield was related to broader range of OA undermoderate water deficits. However, there was no similar association under severewater deficit.3. Our results showed the threshold range of nHRS was positively correlated withOA (r=0.93, P＜0.05). The cooperative relation between threshold range of nHRSand OA is suggested as a mechanism for adapting to drought, which improves grainformation under water stress for spring wheat varieties.4. The severity of drought determined the strategies of plant adaptation to waterstress. During the progressive soil dying, the non-hydraulic root-sourced signals was firstly responsive to the soil drought, which reduced water loss by decreasing stomataaperture, and the threshold range of non-hydraulic root-sourced signals could increasethe MRGY of spring wheat varieties under water stress. With the commencement ofHRS, the regulative role of nHRS for stomata could be weakened, while OAreinforced the ability of spring wheat varieties' defense to drought by accumulatingthe osmotic substances in the leaves. The MRGY was associated positively with theability of OA under moderate water stress. When soil water deficit became severefurther, the ability of OA could be impaired under severe water-stressed levels, whichled to the uncertain relationship between the MRGY and the ability of OA. However,the cooperative relationship between the threshold range of nHRS and the ability ofOA was beneficial for improving the MRGY under water stress.5. Spring wheat WUE was higher for modern than for old varieties, and waspositively correlated with root efficiency and root water uptake efficiency, comparedwith a marked negative correlation between WUE and root weight.6. nHRS is production of natural selection and artificial selection increased thethreshold range. Previous conclusions that the intensity of early-warning nHRS hasbeen weakened during anti-drought breeding, which cannot suffer from the differentgrowth medium of present study. An important reason for this weakening may behigher ABA content, from the onset of nHRS to the onset of HRS, for HST comparedwith LC8275 and GY602, but with a narrower threshold range of nHRS. Modernvarieties exhibited stronger sensitivity to drought by synthesizing moderate amountsof ABA quickly.7. nHRS is the only 'early warning' signal of imminent drought. Redox signals andROS were the second messengers induced by nHRS, and no observable changeoccurred at the commencement of nHRS.8. There were three defense phases for plant subjected to progressive drought:threshold range of early warning was defined as the first phase (from thecommencement of nHRS to the onset of HRS) of early defense. ROS and enzymeactivities did not increase significantly, but there was enhancement of ABA. Therewas positive defense by stomatal closure mediated by ABA and no change in MDA content-indicating absence of membrane lipid peroxidation. A second phase ofdefense may occur from decreased leaf water potential through to TW. ROS andenzyme activity increased markedly, but MDA content increased mildly; injury byROS was not completely detoxified by enzyme activity, indicating disturbedequilibrium. This second defense phase was passive, with membrane injury. The thirdphase (from the commencement of TW to the outset of PW) is defense collapse.The present study is important to illuminate physiological mechanisms to waterand drought resistance, to cultivate spring wheat varieties and improve cropproduction in semiarid regions.