Effect of N top-dressing on protein content in japonica and indica rice grains

The accumulation and distribution of N-15 in the protein and protein fractions of rice grains were investigated by N topdressing at three stages: panicle initiation, heading (HD), and HD+20 days. A traditional tall indica and a semidwarf japonica rice variety treated with two levels of basal N were used for the investigation. Topdressing of N increased crude protein and each protein fraction in the grain. The amount of increase was considerably greater in the indica than in the japonica variety. The top-dressed N-15 partitioned most effectively to the glutelin fraction when it was applied at the HD stage. On the other hand, N-15 applied at HD+20 days contributed more to increased prolamin. Topdressing of N was effective in obtaining rice grains with high quality protein (high glutelin content) in the indica variety, especially when N was top-dressed at HD and HD+20 days.