Fluctuation of Endogenous Gibberellin Levels in the Early Development of Rice

The endogenous gibberellins (GAs) of rice were analyzed during seed germination and during the regeneration of plant lets from embryogenic cells. Four 13-hydroxylated (13-OH) GAs (GA53, GA19, GA20, and GA1) were identified by combined gas chromatography-selected ion monitoring (GC-SIM) from the seeds at every stage of germination examined. A significant increase in their level was observed at the time shoot elongation started. No GA was detected in the embryogenic cells before transferring into a regeneration medium, while the occurrence of 13-OH GAs was confirmed by full-scan GC-MS or GC-SIM during the regeneration of plantlets. These results indicate that the early-13-hydroxylation pathway of GA biosynthesis operated during embryo development and seed germination.