The Positional Effects of Auxin and Cytokinin on the Regulation of Rice Tiller Bud Growth

Auxin and cytokinin (CTK) play important roles in the regulation of rice (Oryza sativaL.) tiller bud growth. Auxin inhibits bud growth and CTK promotes growth; however, little is known about the positional effects of these hormones in the regulation of rice tiller bud growth. In the present study, indole‐3‐acetic acid (IAA) and 6‐benzylaminopurine (6‐BA) (a synthetic CTK) were applied to different leaves and roots at the tillering and heading stages of rice development, and the growth of rice tiller buds on the unelongated and elongated internodes was measured. Additionally, hormonal variations of the plants were examined and recorded. The objectives of the present study were to investigate the positional effects of auxin and CTK on the regulation of rice tiller bud growth. The results indicate that IAA has a notable positional effect on the regulation of rice tiller bud growth, and the positional effect of IAA was closely related to its polar transport. An increase in leaf IAA levels inhibited the growth of tiller buds located at unelongated nodes; however, growth of tiller buds at elongated nodes was inhibited only when IAA levels were increased in the upper‐stem leaves or the leaves at which the tiller bud was located. Contrary to IAA, 6‐BA had no positional effect on rice tiller bud growth. Application of 6‐BA to different leaves and roots significantly promoted the growth of rice tiller buds at both unelongated and elongated nodes.