| The effect and its mechanism of temperature during grain filling on rice quality were investigated by using 4 ear]y-indica rice cultivars with different quality and amylose content. The plants at filling stage were transferred into two phytotrons (Model PGV-36, CONVIRON, Canada), which were set two mean daily air temperatures, i.e. 22℃, optimum temperature regime and 32℃, designed as high temperature regime. The differences in quality properties and starch characteristics of rice between two temperature regimes were determined, and effects of temperature at grain-filling stage on starch biosynthesis in developing rice grains were also analyzed. The main results were as follows:1. The effect of temperature during grain-filling on quality of early-indica rice was significant and high temperature lead to the distinctly deteriorated quality. The head milled rice rate in high temperature treatment was significantly decreased relative to that in optimum temperature treatment. High temperature also caused reduction in both milled and brown rice rates. Thus the milling quality of the rice filled under high temperature was inferior to that filled under optimum temperature. In addition, high temperature deteriorated appearance quality. The chalky rice rate and chalkiness size of rice were highly significantly increased. The effect of temperature on apparent amylose content (AAC) and gel consistency (GC) in milled rice appeared to be cultivar-dependant. Under high temperature, AAC was increased or little changed for the cultivars with higher AAC and decreased for the cultivars with lower AAC. On the other hand, GC values was reduced or remained little changed for the cultivars with higher AAC and increased for the cultivars with lower AAC under high temperature. Moreover, high temperature significantly increased the gelatinization temperature (GT) of all cultivars. It may be concluded that the eating and cooking quality would be markedly inferior when early-indica rice was exposed to high temperature at grain filling stage.2. The effect of temperature during grain-filling on physicochemicalcharacteristics of starch in early-indica rice was significant and it is probably the main reason for inferior quality, especially eating and cooking quality, under high temperature. The crystalline characteristics of starch were affected by temperature in that the relative crystalline degree, the intensity at 18°2θ of X-ray diffraction pattern, and the amount of crystalline structure with densely-packed starch were all higher in the high temperature treatment than in the optimum temperature treatment. The onset temperature (T0), peak temperature (Tp), conclusion temperature (Tc) and gelatinization enthalpy (AH) in DSC thermogram of rice starch were higher for the samples of high temperature regime than for the samples of optimum temperature. Thus, the rice filled under high temperature was general difficult to be gelatinized. The rice starch pasting properties were also affected by temperature. The cool paste viscosity (CPV), setback (SB), and consistency (CT) in RVA profile of rice starch were much lower for the plants exposed to high temperature than for the plants at optimum temperature.3. The effect of temperature during grain-filling on starch fractions and granule properties of early-indica rice was significant, which may be attributed to the changes in physico-chemical characteristics of starch sue to exposure of high temperature. Temperature also affected starch chain-length distribution of early-indica rice. The long B-chain content was dramatically increased and the intermediate B-chain content decreased under high temperature. Moreover, high temperature lead to an increase in amount of big starch granules and the mean diameter of starch granules, while a reduction in the amount of small starch granules. It may be assumed that these changes affected physico-chemical characteristics of starch in rice, as a consequence, resulting in inferior quality.4. The effect of...
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