Effect Of Soil Moisture On The Development Of Rice Quality And Its Mechanism

Based on the pot and field experiments by rigorously controlling soil water potential with tensionmeters for the cultivars applied in production and transgenic rice plants with anti-sense Wx gene and original variety WuyunjingJ (9522), the regulating effects of soil moisture on the development of rice quality were examined. The dynamic changes of starch (including amylose and amylopectim), protein and the activities of key enzyme involved in the synthesis under different soil water potentials were analyzed in this paper, and the effects of soil moisture on the structure of starch granule, the characteristics of RVA profile of rice flour and the texture of cooked rice and the reasons of the increase of chalkiness were studied. The index of intermittent irrigation for the production of high quality rice was brought out, which provided the scientific reference for the establishment of the technique regulating the high quality by irrigation. The effects of severe water stress (dry cultivation) on the main characters of grain quality were observed, which could offer the theoretically reference for the selection of the varieties with high quality in dry cultivation, and could supply the premise condition for the popularization of dry cultivation. The main results indicated:1. The relations of soil moisture (or soil water potential) with the character of rice quality during grain filling were defined, and the effect of the activities of source and sink on the grain quality were proved up. During the grain filling period, when the soil water potential (SWP) was reduced to -15kPa, head milled rice was significantly increased, gel consistency become soft and no obvious effects on the percentage of chalky grain and chalkiness were observed. While SWP was less than -SOkPa, head milled rice was significantly decreased, both the percentage of chalky grain and chalkiness were significantly increased. There was a conic relationship between gel consistency and SWP, and no significant difference among treatments in other quality indices, such as kernel shape, amylose and protein content, were found. There were obviously changes in leaf to spikelet ratio, chlorophyll content and grain water content during grain-filling period. If the low soil water potential was under -30kPa, the relative dispersion of leaf to spikelet ratio and chlorophyll content were presented negative effects during the 25-35 days after flowering, dehydration of kernel wasvery rapid, which had an effect on both the production of photoassimilates and the accumulation of starch and resulted in the reduce of head milled rice and the increase of chalkiness.2. Effects of soil water stress on the main characters of superior and inferior grains quality and the properties of RVA profile during grain-filling period were examined, and the morphological microstructure of starch granule and the parameters of grain filling subjected to water stress were analyzed. When the soil water potential (SWP) was at -20kPa, the grain weight of superior and inferior kernel in two cultivars was at its most, and the chalkiness was at its least. There was no obvious change in the milling and cooking quality and the nutrient quality was improved. The trend of high quality was observed. When the SWP was declined to -60kPa, the weight and head milled rice of superior grains (SG) and inferior grains (1G) and the amylose content of 1G were decreased significantly, stiffer gel consistency, bad taste quality and low rice quality was found. Effects of SWP on the RVA characteristics of the different grains in a panicle varied with the kernel position, there was no significant difference in the RVA profiles of SG between the treatments, but the obvious difference was observed in the RVA profiles of IG between the treatments, and especially when the SWP was decreased to -60kPa, the visible changes of the RVA characteristic value were detected, the viscosity under -60kPa was much less than that under well water. Effects of SWP on the shape, size, structure of starch granule in the grain transec...