Cytokinin concentration gradient in the developing grains and upper leaves of rice (Oryza sativa) during grain filling

摘要

Changes in cytokinin activity in the flag, first, second, and third leaves and in the developing grain of rice (Oryza sativaL.) were studied using the soybean callus bioassay in relation to the movement of photosynthate during different developmental stages. Cytokininlike activity in leaves was highest at the 85th day after transplantation. The flag leaf maintained higher cytokinin activity than other upper leaves. In grains high cytokininlike activity during the 1st week after anthesis is correlated with the grain setting and cell division period. The concentration gradient of cytokininlike substances in the upper parts of the plant was highest in the panicle after anthesis. The data suggest that the developing rice grains attract most of their photoassimilate from their nearest neighbours, the metabolically active flag, first, and second leaves.