Analysis of Physiological Characteristics about ABA Alleviating Rice Booting Stage Drought Stress

Objective The objective of the study is to reveal the drought tolerance mechanisms of different rice varieties and the physiological mechanisms about ABA reliving rice drought stress.Method Japonica drought tolerance rice Zaoyuxiangjing and conventional japonica rice Nanjing44 were pot planted until booting stage, and 150 mg·kg-1 of abscisic acid(ABA) was sprayed on leaf to study the influence on rice antioxidant enzyme activity(SOD, CAT), membrane lipid peroxidation(MDA) content, net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), chlorophyll and soluble sugar(SS)content, biomass accumulation, yield per pot and yield components. Finally, their different biological and physiological drought resistance and response to ABA treatment were compared.Result During drought stress, rice maintained higher SOD and CAT activities, leading to a lower MDA content to a certain extent. They synthesized higher soluble sugar content to maintain cell osmotic adjustment. The leaf net Pn decreased consistently. Gs also showed a downward trend with increasing water stress, and Tr consistented with the Gs. Chlorophyll a synthesis was inhibited, and the content decreased. The result showed that dry matter accumulation and yield per pot were decreased significantly compared with CK. Two varieties showed significant differences in response to drought stress, and Zaoyuxiangjing was more drought resistant than Nanjing44. When ABA treated, Pn and dry matter accumulation were reduced in short time. While SOD activity was further improved, leading to reduction of MDA accumulation. Meanwhile, exogenous ABA induced stomatal closure during drought stress and reduced transpiration rate, the excessive water consumption was reduced and water use efficiency was improved, thus having a significant protective effect on rice, reduced the metabolic function of drought on rice physiological damage, and accelerated functional recovery after rehydration, keeping higher content of chlorophyll a to prevent leaf premature. The effect of ABA treatment was more significant on Zaoyuxiangjing. Its Pn, Gs and Tr recovered quickly after rehydration and a significant increase in chlorophyll a content. ABA also promoted its soluble sugar synthesis and dry matter accumulation more faster under drought stress, then improved its grains of per panicle, filled grain rate, 1000-grain weight and grain yield per pot significantly. ABA effect was weaker on Nanjing44 because of its general drought resistance. Nanjing44 was susceptible to drought stress, less sensitive to ABA, slow physiological and growth characteristics recovery. Although ABA significantly increased Nanjing 44 grains per panicle, filled grain rate and 1000-grain weight, it did not significantly increase the yield per pot.Conclusion The short-term dormancy effect on rice of ABA could relieve the physiological metabolic function damage of rice under booting stage stress effectively, promote its functional recovery after rehydration, and mitigate the effects of drought on yield. There were differences in the response to ABA between different drought resistance varieties. The stronger drought resistance variety was more sensitive to ABA and displayed better result to exogenous ABA.