Effects of Gibberellin on the Morphogenesis in Rice Plants : 2. Morphological abnormalities which appeared in spilkelets.

Abstract

It was found that various morphological abnormalities as shown in figures 1-14 were caused by gibberellin in rice spikelets when it was applied to rice plants at the concentration of 100 ppm, mixed in nutrient solution at the stage of young panicle differentiation. The morphogenetic effects of gibberellin on the spikelet formation are summarized as followings: (1) multiplication of organs which constitute a spikelet, (2) fusion of organs, (3) deformation of organs in shape and size, (4) appearance of the extraordinally swelled tissue or organ and (5) occurrence of disorder in the relative position of organs on the axis. Concerning to the multiplication of organs, it was not chaotic but showed some tendency to revelate an ancient type of spikelet in gramineae, that is, a structure having multiple florets in one spikelet. Based on the tendency above mentioned and some other phenomena, these are, development of the bract leaf and the third stigma which are degenerate and do not develop under the common cultivating condition, the remaining behavior of empty glumes to the axis when the mature grain falls away as shown in figure 1, etc., gibberellin-like substances were seemed to have close contacts with the manifestation of degenerate or degenerating characters in rice plants. Comparing the gibberellin induced abnormalities with those which are said to be genetic and single gene recessive characters in some special varieties-some examples are shown in figures 15-17, and which are caused by a cool water (13-15°C) treatment as shown in figures 18 and 19, it is considered that gibberllin may have some physiological role in the express of genetic characterst in these varieties and in the occurrence of abnormal spikelets under an unusual low temperature, because they have close resembrances in many faces.