Studies On The Quality For The Grains At Different Positions Within A Panicle And The Relationships Of Enzymatic Activities In The Grains With Cooking Quality Of Rice

With typical rice cultivars as materials, the distribution of the quality for the grains at different positions within a panicle and the changes in activities of the key enzymes involved in starch synthesis in grains during grain filling and their relationships with cooking quality were investigated. The main results are as follows:1. There were significant differences in rice quality among the grains at different positions within a panicle. The distribution of the quality varied with cultivars and the amount of nitrogen (N) applied. Under the normal amount of N application, the change in grain weight was associated with following sequence of a grain. In general, the spikelets that flower earlier produced greater grain weight than those flower later. However, the change in grain weight was not very identical with the following sequence, and sometimes the spikelets with later anthesis also produced greater grain weight than those with early anthesis. Generally, the percentages of milled rice and head rice and gel consistency were greater or higher for the grains at the top and mid parts than those at the base part on a panicle, and greater or higher for the grains with early anthesis than those with later anthesis at a branch. The results were reversed for amylose content, chalky grains and chalkiness of grains. The grain with the earliest anthesis (the first spikelet) at primary branches showed the highest in breakdown and the least in setback values. The breakdown values increased, whereas setback values decreased with the increase in amount of N applied, for the grains at primary branches. No ordered distribution was observed for protein content in grains within a panicle.2. When amount of N applied was ranged from 0 to 240 kg/ha, most characters of rice quality were improved with the increase in N application. The above results indicate that development in high yielding and good quality of rice is able to be coordinated and cultivation practices, such as N-fertilizer application, can improve rice quality.3. The changes in activities of adenosine diphosphoglucose pyrophosphprylase (ADPGPase), starch synthase (SSase) and starch branching enzyme (Q-enzyme) in the grains during the filling exhibited a single peak, and the time of the activity peaks for the former twoenzymes was earlier than that of the maximum grain-filling rate (Tmax), and the time reaching the peak for Q-enzyme was synchronous with Tmax. The activities at early grain filling stage, and the mean and maximum activities of each enzyme during grain filling period were positively and significantly or very significantly correlated with the mean and maximum grain filling rate and starch content (mg/grain) in the grains. Activities of ADPGPase at all grain filling stages and those of Q-enzyme at the early and mid filling stages were not significantly correlated with the gel consistency (GC), alkali spreading value (ASV) and amylose content (AC). SSase activities at the early filling stage were significantly and negatively correlated with GC and ASV, and positively correlated with AC. Activities of SSase at mid and late grain filling stages and Q-enzyme at the late filling stage were significantly and positively correlated with GC and ASV, and negatively correlated with AC. Spraying zeatin or abscisic acid at early grain filling stage could obviously regulate the activities of ADPGPase, SSase and Q-enzyme in the grains, leading to an improvement in cooking quality.