Abstract:

Temperature at grain filling stage has great impact on grain development. It has been well known that high percentage of chalky grains, poor cooking and eating quality may be caused by high temperature during the filling period, which is probably attributed to the shortened duration of grain filling, the low photosynthesis rate and activity changes of some enzymes relevant to grain filling. However, little information has been known about the effect of temperature on main endogenous hormones in developing grains at filling stage, which commonly play an important role in grain development as a growth signal. In this paper, two temperature treatments, i.e. daily average temperature 32℃(High) and 22℃(Optimum), were established to compare the difference in the endogenous hormone levels between two temperature treatments with two early indica rice cultivars applied, aiming to recognize the relationship between the effect of temperature on grain development and the response of endogenous hormone in grains to temperature. The results showed that by higher temperature, grain development was accelerated at early grain-filling stage, and the grain filling duration was shortened (Fig.1). The contents of IAA, ZR, and GA₃ in developing rice grains were dramatically reduced at early grain filling stage when the plants were exposed to higher temperature, while a little difference was found in their contents between two temperature treatments at later stage (Fig.2–4). Compared with optimum temperature treatment, there was much higher ABA content in developing grains throughout the whole filling stage in high temperature treatment in spite of remarkable difference between cultivars (Fig.5). Considering effect of temperature on grain filling process and its relation with hormones levels in developing grain, it could be deduced that the acceleration of grain development and the shortening of grain filling duration should be ascribed to the reduction in IAA, ZR, GA3 contents and the increase in ABA content in developing grains at early grain-filling stage when rice plants exposed to high temperature.

Key words: Grain-filling stage, Temperature, Rice, Hormone