Studies on the Starch Contained in the Tissues of Rice Plant : 12. The effect of air-temperature on the growth, nitrogen and Carbohydrate Constituents.

Abstract

Using two constant-temperature greenhouses of 27° and 17°C respectively, the rice plants were grown under the following four temperature regimes. HH : Grown at 27° continuously. HL : Grown at 27°by day and 17° by night. LL : Grown at 17° continuously. LH : Grown at 17° by day and 27° by night. The treatments, each of 15 days long, were given at three growth stages: (1) the stage of tillering, (2) early panicle development and (3) later panicle development. When treatments ended, the plants of half pots were harvested immediately for chemical analysis and the other half pots were placed out of doors until the plants matured. Besides these, both germinated seeds and maturing plants were treated under warmer and cooler air temperatures, till the former reached to several leaves stage and the latter to the end of maturation. The results obtained are summarized as follows: (1) The plants in HH plot were tallest with the largest area of leaf-blades and the highest speed of leaf emergence, but their dry weight was less than that of HL plants, mainly due to a small number of tillers. The LL treatment depressed the growth of plant in terms of plant height, leaf emergence rate, leaf area and dry weight. The growth of HL and LH plots was intermediate between those of LL and HH. (2) Heading was most advanced in HH plot, and delayed under LL and LH, especially when the LH treatment was given at the stage of early panicle development. (3) The matured kernels decreased in number at LL and LH almost equally in case of the second treatment, however, at the later stage of panicle development which included the pollen formation, the continuously low temperature might have severely damaged the pollen resulting in extremely poor fertilization and fruiting. The LH treatment also heavily decreased the fruiting percentage. (4) In the vegetative stage of growth, the greatest amount of transitory starch was stored in the culm and leaf-sheath in LL plot, followed by the HL and LH. The HH plant had the least of it. During the ripening period, much starch remained in the culm and leaf-sheath when treated under cool temperature presumably because the movement of sugars into grains was inhibited or delayed due to failure of fertilization or lower rate of translocation. (5) The total and soluble nitrogen content were highest in the plants of LL plot, followed by those of HL, LH and HH respectively. As a whole, the plants grown continuously at lower temperature had a higher carbohydrate and nitrogen content than the plants grown under warmer temperature conditions. The plants grown continuously under warmer temperature had a least content of them. However, in young seedlings which depend their growth mostly on the reserves of the seeds, the consumption of endosperm starch and the growth of seedlings seems to be proportionally controlled by air temperatures, resulting in the least storage of transitory starch in the stem or leaf-sheath. (6) The significance of starch contained in the culm and leaf-sheath are discussed in relation to the growth and the ripening of rice plant.