Relationship between Flower Formation and Elongation of Internodes under an Effect of Temperature in Paddy Rice Plants

The experiments were carried out to study relationship between flower formation and elongation of internode in cereals. In the present report, especially, the effects of temperature on flower formation and elongation of internode in paddy rice plants are concerned. In the experiments, rice varieties NORIN No.11, RIKU No.132 and ZUIHO were used as materials. Seeds of each variety were sowed several times in a thermo-controlled green house (18-25°C) and in the open air (15-30°C), respectively. The time of flower formation was indicated by the double-ridge stage of main shoot apex. But, we have no suitable index for elongation of internodes. So the formation of vacant space (inside the tissue of the node) was taken for a sign of elongation of internodes. Dissected stem tips were fixed in F.A.A., and were embedded in paraffin wax. Serial sections cut (at about 15 μ) of them were stained with 1% gentian violet solution. In an early stage of vegetative growth, we observed none of the nodes in the shoot apex. However, small cell bands were observed below the growing point of the apex nearly at the middle stage of vegetative growth. The authors termed it node formation (Plate B). Moreover, the small cell bands splitted then and there appeared so-called vacant spaces among those bands. (Plate C). Finally, visible elongation of internodes was observed. The elongation of internodes in highly thermo-sensitive varieties began at an earlier stage than that in low thermo-sensitive varieties. Namcly, the elongation of internodes in NORIN No.11 occurred at 6-leaves stage, while that in RIKU No.132 and in ZUIHO took place at 10-leaves stage. We observed no alteration in the time of these stages by applying high or low temperatures. So, it could be concluded that temperature has no influence on the node formation in paddy rice, though the growth of plant was remarkably delayed at lower temperatures. On the contrary, the flower formation in high thermo-sensitive varieties (NORIN No.11) were delayed by low temperatures. But, the flower formation in low thermo-sensitive varieties is rather photo-controlled than thermo-controlled. Thus we may conclude that there is no close relations between flower formation and beginning of elongation of internodes in paddy rice plants, though visible elongation of internodes is stimulated by flower formation