Changes in the Negative Gravitropic Response of Main Shoot in Relation to Growth Stages in Rice

Abstract

Plants were grown in pots containing soil. Every tiller was cut off when it emerged and only the main shoots were allowed to grow. Exp. 1. Plants in pots were artificially placed horizontally at different growth stages and the pots were kept in a horizontal position until the shoot kneeing was compoeted. The shoots were completely recovered by their kneeing abilities in the pulvini to a vertical position when the plants were placed horizonatlly between 7th leaf-stage (plants had 7 leaves on a main stem) and the time of panicle heading. Then the plants gradualy lost their kneeing ability during the time of grain ripening. With an increase of growth stages the position of the responded pulvinus was elevated and the number of pulvini that responded was decreased. The persistency of kneeing ability of each pulvinus of the elongated internode was longer than that of non-elongated internode. Exp. 2. The bending up of a shoot was increased when their panicles were cut off at the same time when lodging treatments started. However, it was decreased when the panicles were cut off 2-3 weeks before the lodging treatments. In addition the silica accumulation in the responded pulvinus was enhanced by the panicle removal. These results suggest that the increase in a panicle weight and the accelerated deposition of silica in the pulvinus depresses the movement of the rice shoot axes to upright position.