Effect of Plant Growth Regulators on Growth of Rice Tiller Bud and Changes of Endogenous Hormones

The objectives of this study were to investigate the changes in plant hormones during tiller bud growing in rice (Oryza sativa L.) and the mechanism that underlies the effect of hormonal regulation on tiller bud growth. Rice cultivars Yangdao 6 (indica) and Nanjing 44 (japonica) were used to investigate the effects of exogenous abscisic acid (ABA, 50 mg L⁻¹), gibberellic acid 3 (GA₃, 50 mg L⁻¹), and α-naphthalene acetic acid (NAA, 50 mg L⁻¹) on tiller bud outgrowth and the changes of endogenous hormones. After foliar spray of the exogenous hormones, the tiller bud growth was completely inhibited in treatments of GA₃ and NAA applies; but exogenous ABA application slowed down the growth rate of tiller bud. Both exogenous GA₃ and NAA increased the ABA contents in tiller node and tiller bud and decreased the zeatin + zeatin riboside (Z+ZR) contents. Exogenous GA₃ increased the IAA content in tiller node; besides, the variation of IAA and Z+ZR occurred earlier than that of ABA. Suggestively, these 3 endogenous hormones are closely associated with tiller bud growth, of which only IAA and Z+ZR play key roles, although ABA can affect the growth velocity of tiller bud. Exogenous hormones regulate tiller bud growth through changing the contents of endogenous ABA, IAA, and Z+ZR in rice plant.