| Research Abstract |
Rice (Oryza sativa L. cv. Koshihikari) and azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) seedlings were grown under various temperature conditions and the mechanism inducing the difference in growth rate was analyzed. When both seedlings which had been grown in the dark at 30℃ were transferred to the temperature range of 10-50℃ and grown further, the growth rate of rice coleoptiles and azuki bean epicotyls was maximum at 40℃ and 30℃, respectively. The cell wall extensibility was also the highest at such temperatures, and became smaller as the temperature increased or decreased. There were close correlations between the growth rate and the extensibility of both materials. On the other hand, the cellular osmotic concentration of rice coleoptiles and azuki bean epicotyls was lower at the temperatures where the growth rate was high. These results suggest that the growth rate of plant shoots is mainly determined by the mechanical properties of the cell wall in the moderate, physiol
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ogical temperature range.
In rice coleoptiles, the levels of cell wall polysaccharides per unit length were the highest, whereas the molecular mass of the hemicellulosic polysaccharides was the lowest at 40℃. The activity of (1→3), (1→4) -β-D-glucan degradation was the highest at 40℃, and decreased as the temperature increased or decreased from this temperature range. These data suggest that in rice coleoptiles temperature regulates the cell wall extensibility mainly by affecting the activity of (1→3), (1→4) -β-glucan degradation. On the other hand, in azuki bean epicotyls, there were no clear changes in the levels of cell wall polysaccharides per unit length of epicotyls, or the molecular masses of the pectin or the HC-I polysaccharides, irrespective of temperature. However, the molecular mass of the HC-II polysaccharides was the lowest at 30℃. Xyloglucan-degrading activity in azuki bean epicotyls was highest at 30℃, and decreased as the temperature increased or decreased from this temperature range. Thus, in azuki bean epicotyls temperature in the moderate, physiological range was shown to regulate the cell wall extensibility mainly by affecting the activity of xyloglucan degradation. Less
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