Identification of gibberellins in the rice plant and quantitative changes of gibberellin A19 throughout its life cycle.

The major endogenous gibberellin (GA) in shoots, roots and ears of the rice plant, Oryza sativa L. japonica cv. Nihonbare, was identified as GA19 by combined gas liquid chromatography-mass spectrometry (GC-MS) and GC-selected ion current monitoring (GC-SICM). Another GA present in these tissues in small quantity was tentatively identified as GA1 by GC-SICM, and GA4 may be present in the seeds (kernels) of 3rd-leaf-stage seedlings. Using GC-SICM, the GA19 content was quantified throughout the life cycle of rice plants. It was found to reach high levels (ca. 10-15 μg/kg fresh weight) in 3rd-leaf seedlings, at panicle initiation (shoots), and during heading and anthesis (ears). The levels of GA19 in Oryza sativa indica cv. T-136 underwent changes closely similar to those found in Nihonbare. The growth-promoting activity in rice of exogenous GA19 is generally considerably less than that of GA1. It therefore seems possible that GA19 functions as a "pool GA". The level of active GAs such as GA1 may be regulated by the rate of biosynthesis of GA19 or its metabolic conversions.