Vegetative Proliferations of Floral Spikelets in Oryza sativa L. : V. Seasonal change of the type of proliferations which differentiate in the spikelets of a mutant induced by X-ray irradiation

The study was carried out to make clear the seasonal change of the type of proliferations differentiated in the spikelets of a mutant induced by X-ray irradiation. Results obtained were as follows: 1. Morphological changes seen in the spikelets of the mutant: (1) The number of vascular bundles had increased both in empty glumes and lemma than usual, and additional differentiation of glumes was too recognized through all seasons. (2) The degenerating tendency of stamens appeared presenting a striking contrast to the increase of glumes mentioned above. (3) Most of spikelet-type (S-type) proliferation occurred from July to October and leafyshoot-type (L-type) one occurred from January to March, showing a striking difference in the type of proliferations by seasons. (4) Especially on December that is the intermediate period when the type of proliferations transformed from the S-type into the L-type, pistilate organs increased remarkablly in a spikelet and the pistil-type (P-type) proliferation appeared. 2. Spikelets obtained from normal strain had also various morphological abnormalities, suffering from the influence of low temperature. 3. Refering to the seasonal change of day length through a year, the S-type proliferation occurred on the decreasing period of day length, the L-type one on the increasing period of it, and appearance of the P-type proliferation coincided with the transition period of day lengh from shortening to lengthening one. From the facts above mentioned, we might be able to draw following schemes on the influence of temperature and day length upon the type of proliferations : a. Moderate (or high) temperature + day length inclining to short day → the S-type proliferation b. Low temperature + short day → the P-type proliferation c. Low temperature + day length inclining to long day → the L-type proliferation Since the stage enhanced the differentiation of pistilate organs most remarkablly was followed by that of vegetative proliferation, it was considered that both the P-type proliferation and the L-type one were seemed to be a series of phenomena having a common physiological back ground, and the change of the type of proliferations might be induced by the enhancement of endogenous auxin level. On the significance of the development of proliferations in the spikelets, some discussions were undertaken from the point of the mode of propagations in rice plant.