Vegetative Proliferations of Frolal Spikelets in Oryza sativa L. : II. The proliferative structure in the spikelets of the mutant strain induced by X-ray irradiation

Abstract

The present study was undertaken to determine the fundamental structure of the proliferations common to the Spikelet-type having spikelet-like organ(s) in it and the Leafy-shoot-type having leafy shoot composed of a number of leafy glumes alternately, and to determine the type of proliferations by the analysis of positional relation between rachilla and the proliferative axis. Results obtained were as follows; 1) The number of empty glumes was increased generally, followed by the increase of the veins in them. 2) Both lower and upper lemma, the latter was corresponding to palea due to its position, had a variety of axillary organs in their axillae, and the frequency of their organ differentiation was increased acropetally. 3) In the half number of the S-type proliferation, the form of the shoot apex was vegetative, showing the transformation into the L-type one. 4) The organs had a 1/2 phyllotaxis in both S-type and L-type proliferations. 5) The L-type proliferation had spikelet-like organs similar to the S-type one at the basal portion of the S-type one. 6) Adventitious roots were recognized at the basal portion of proliferated spikelets and leafy-shoots. As mentioned above, the type of proliferations found in this experiment was recognized to be diaphysis which was induced by the apical growth of the shoot apex of rachilla, judging from that the phyllotaxis were the same both in the rachilla and proliferative axis, and the proliferative axis were situated on the extention line of the rachilla and corresponded to the main axis as seen from the upper lemma position. The proliferative structure common to the S-type and the L-type were, therefore, as follows: 1) development of the proliferative axis by apical growth of rachilla differentiating more spikelet-like organs than usual, 2) spikelet-organs were differentiated on the tip of the proliferative axis, 3) their organs were arranged with a 1/2 phyllotaxis from rachilla to the proliferative axis consistently. The proliferation of this experiment, therefore, was grasped as a process of the vegetativation caused by the development of rachilla, and the L-type proliferation was seemed to be a transformed type of the S-type of which the shoot apex continued to differentiate vegetative glumes indefinitely. From the point of the morphogenesis of spikelets, those proliferations were considered to be results of a conversion of growth stage from the differentiation-stage of glumes into that of rachis or spikelet just before the time of differentiation of stamen or pistil. Some discussions were given of the development of the proliferative-body into an independent plantlet, and the signicance of the initiation of adventitious roots.