Abstract
Developmental analyses were investigated on the occurrence of the abnormal spikelets caused by low temperature about 14-18°C using rice cultivars "Sachikaze" and "Rikuu 132". The various morphogenetic abnormalities of spikelets were induced by the low temperature when they were treated at the stage of their primordial differentiation, from 3 to 2 weeks before heading time. The increments of florets in a spikelet were observed frequently in the panicles which were treated at the earlier stage of their development and on the other hand the increments of floral organs in a spikelet were observed frequently in the panicles which were treated at the later stage of their development. Since the increments of florets and floral organs had also been clarified to be induced by gibberellin treatment, it was considered that the level of gibberellin-like substances is enhanced in the meristematic regions of spikelet primordia by low temperature and they brought about different influences in the morphogenesis of spikelets depending upon the developmental stages when they were set under low temperature conditions.
