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

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Abstract
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.