Dynamics of starch formation and gene expression during grain filling and its possible influence on grain quality.

In rice, grain filling is a crucial stage where asynchronous filling of the pollinated spikelet's of the panicle occurs. It can influence both grain quality and yield. In rice grain, starch is the dominant component and contains amylose and amylopectin. Amylose content is the chief cooking quality parameter, however, rice varieties having similar amylose content varied in other parameters. Hence, in this study, a set of varieties varying in yield (04) and another set (12) of varieties that are similar in amylose content with variation in gel consistency and alkali spreading value were used. Panicles were collected at various intervals and analysed for individual grain weight and quantities of amylose and amylopectin. Gas exchange parameters were measured in varieties varying in yield. Upper branches of the panicles were collected from rice varieties having similar amylose content and were subjected to gene expression analysis with fourteen gene specific primers of starch synthesis. Results indicate that grain filling was initiated simultaneously in multiple branches. Amylose and amylopectin quantities increased with the increase in individual grain weight. However, the pattern of regression lines of amylose and amylopectin percentages with increase in individual grain weight varied among the varieties. Gas exchange parameters like photosynthetic rate, stomatal conductance, intercellular CO