Vegetative Proliferations of Floral Spikelets in Oryza sativa L. : VIII. Influence of temperature on the proliferation of spikelets.

Abstract

This experiment was carried out to make clear the influence of the height and diurnal range of temperature on the morphology of spikelets in normal rice plant, cultivars Akibare and Reimei, and on the type of proliferation in their mutant strains, both of which have been cultivated in green house or phytotron under natural daylength of summer and winter. It was observed on the normal strains that from about eight to twenty nine percent of spikelets botained in winter in green house and phytotron of low temperature developed their glumes; remarkable elongation and multi-venation of empty glume and lemma or differentiation of awn, contrasting the ones in summer having scarcely such develped one. On the mutant strain induced from cultivar Akibare, it was observed that in winter every spikelets in green house and phytotron developed the same kind of glumes as in normal strains, although in summer relatively fewer ones in green house did those glumes than in phytotron. As for the mutant strain of cultivar Reimei, it was clarified that in summer most part of spikelets in phytotron of low temperature differentiated pistil-type (P-type) proliferation in contrast with most of them in green house did spikelet-type (S-type) one, and in winter about twenty seven percent of spikelets in phytotron of low temperature did leafyshoot-type (L-type) one which was hardly observed in other experimental conditions of this study, besides most part of them in not only phytotron but also green house did P-type one. Considering that the proliferation progressed gradually to vegetative characteristics as the type changed from S-type to L-type going through P-type, results mentioned above suggested that small diurnal range of temperature particularly under lower one might promote more effectively the changing type of the proliferation into vegetative than larger diurnal one. Comparing those results with those of the effect of gibberellin and/or naphthalene acetic acid on the proliferation which had been reported previously by the authors, it was considered that proliferative changes induced by low temperature, its small diurnal range and short day seemed to have similar physiological back ground with that induced by those growth substances. Some discussions were undertaktaken on the fact that phenomena of spikelet proliferations in Gramineae had been observed mostly in Festucoid than Panicoid by many workers.