Regulation Mechanisms Of ABA On Grain Development And Activity Of Sucrose Synthase Of Inter-subspecies Hybrids

Inter-subspecies hybrid rice has stronger growth potential and higher biomass. However, poor grain filling is often observed in these hybrids and limiting the further increase of grain yield and their applications and extensions in rice practice. Therefore, it is urgent to explore the mechanisms of regulating grain filling of inter-subspecies hybrid rice. Further improvement in rice grain filling depends to a large extend on our understanding on the physiological and biochemical processes of grain filling in rice and their regulatory mechanisms. In present study, we mainly concerned the roles of ABA in the regulation of grain filling of hybrid rice (Japonica×Indica), using root-split system as well as exogenous applications of ABA and ABA synthesis inhibitor, fluridone, during the period of grain filling. The main results are as follows:1. Grain filling processes of superior and inferior grains of two hybrid rice varieties, i.e. Liangyouepeijiu and Shanyou 63, displayed to be in a asynchronous pattern, that is, the initiation of grain filling of superior grains was earlier than that of inferior grains, and mean grain filling ratio, maximum grain filling rate of superior grains were higher than those of inferior grains. Similar trends in endogenous ABA content, activities of sucrose synthase and Q-enzyme were observed in superior and inferior grains during grain filling period.2. The results of root-split experiments of which half-roots were exposed to drying condition and another half roots normally irrigated, showed that the leaf water potential was almost similar to that of control treatment (whole root system was irrigated), whereas endogenous ABA content of grains was significantly higher than the later. As compared with those of half root-dried and control treatments, the leaf potential substantially decreased and endogenous ABA content of grains significantly increased for whole root system dried treatment. Half-root dried treatment significantly stimulated grain filling, and thus the final grain weight of inferior grains, but not of the superior grains. Furthermore, the sucrose metabolism and the activities and expression of sucrose synthase were also stimulated by half root dried treatment.3.Appllication of fluridone, an inhibitor of ABA synthesis, at 8~13d post-anthesis significantly reduced endogenous ABA content, grain weight and sucrose synthase activity and application of exogenous ABA had stimulated effects on grain filling and sucrose synthase activity.According to above results, it was suggested that ABA played vital roles in the regulation of grain filling, which was largely thrugh afftecting sucrose metabolism of grains.