Rice Grain Filling And Stem And Sheath During The Non-structural Assimilates Accumulation And Its Regulation

The dynamic changes of temporary nonstructural reserve in stem-sheath of rice during grain filling and their relations to changes of the activities of enzymes catalyzing starch hydrolysis and sucrose biosynthesis were investigated using 4 rice varieties with different source-sink relations, Liangyoupeijiu (LYPJ), Shanyou 63 (SY63), Wuyujing 3 (WYJ3) and New-plant-type (XZX). In addition, the effects of soil drought and leaf-cutting and spikelet-thinning treatments on the accumulation and export of non-structural reserves and the activities of related enzymes of stem-sheath of rice were also studies. The results showed that(1) The dry weight of stem-sheath of LYPJ, WYJ3 and XZX rice varieties increased during early stage of heading and then decreased as the grain-filling progressed. During the later stage of grain filling, re-accumulation of stem-sheath reserves in these varieties was observed in terms of dry weight of stem-sheath. However, the dry weight of stem-sheath of SY63 decreased upon heading and no re-accumulation was detected in present experiment.(2) The starch content in stem-sheath of XZX variety was significant higher than other three rice varieties tested during grain filling. Total soluble sugar content decreased gradually after heading. But accumulation of total soluble sugar was detected after 24 days of heading. Similar trends in the dynamic changes of sucrose content in stem-sheath were observed.(3) The different grain to leaf area ratio has obvious influences on the content non structural sugars in stem-sheath, especially on starch and total soluble sugar content, and this influence varied greatly with the different stages of grain filling. The starch and total soluble sugar contents, but not sucrose content, decreased as the increase in grain to leaf area ratio. The decrease in starch and total soluble sugar contents was more great in rapid grain-filling stage (10 days after anthesis) than in the early grain-filling stages.(4) The effects of soil drought on the content of non-structural sugar in stem-sheath of rice varied with different rice varieties. The starch content in stem-sheath of draughted LYPJ variety was higher than that of irrigated treatment. Reverse result was observed in XZX.(5) The activities of a-amylase increased as the progression of grain-filling and draughted treatment obviously raised the activities of a-amylase. However, the P-amylase activities decreased with the progress of grain filling process and inhibited by drought treatment.According to the above results, it is suggested that the accumulation and exported of non-structural sugars in stem-sheath of rice varied greatly with different rice varieties, and the activities of a-amylase and P-amylase were the main determining factors which affected the export of non structural sugar from stem-sheath to grains. The effects of drought and other treatments on the export of non structural sugar from stem-sheath to grains were determined greatly through their effects on these enzyme activities.