Fluctuation of the endogenous IAA level in rice during its life cycle.

Abstract

Endogenous auxins in the shoots and ears of rice were investigated. Indole-3-acetic acid (IAA) and indole-3-carboxylic acid (ICA) was identified by GC-MS, the endogenous level of IAA being much higher than that of ICA. To analyze the fluctuation of endogenous IAA level throughout the life cycle of rice, a rapid and effective procedure, using HPLC and a fluorescence detector, was developed. The level of IAA in shoots was 10 —26ng/g fr. wt., while that in ears was 10 to 100 times higher. The level of IAA conjugate in ears was also much higher than that in shoots. These results show that the biosynthesis of IAA occurs at an early stage of seed development, and it is also suggested that IAA may play a role in regulating the reproductive growth of rice.