Effect of light period longer than critical day length after heading on the growth and development of rice under a controlled environment.

摘要

Rice varieties have been genetically modified to produce pharmaceutical proteins in seeds. Such production requires pharmaceutical proteins to be expressed in high concentrations and to remain stable. This can be achieved by controlling the growth environment by using a closed plant production system. In order to produce large amounts of pharmaceutical proteins, one must determine the environmental condition requited to increase the growth of plants or the concentration of pharmaceutical proteins in seeds. The present study focused on determining the conditions for optimizing the growth of plants. Rice is a short-day plant. When the light period is constantly controlled such that it becomes longer than the critical day length, flower formation is delayed and growth period is prolonged, with no effect on the promotion of photosynthesis. Therefore, if the light period is regulated to exceed the critical day length only after the heading stage, enhanced photosynthesis would be achieved without the inhibition of flowering. The present study investigated the effect of light period on the growth and development of rice after heading. Rice plants at 65 d after germination - just after heading - were grown in growth chambers for 46 d under 3 different light periods (12, 16, and 20 h d-1) under controlled environments. The number of tillers observed when the plants were grown under 16 and 20 h light d-1 was greater than that observed when the plants were grown under 12 h light d-1, but the highest number of ears were observed when the plants were grown under 12 h light d-1. The shoot dry weight of plants grown under 12 and 16 h light d-1 was greater than that of plants grown under 20 h light d-1. The ratio of seed dry weight to shoot dry weight and the number of ripe seeds also increased when the plants were grown under a shorter light period. These findings suggested that when the light period became increasingly longer than the critical day length, the rice plants showed a tendency to promote vegetative growth over reproductive growth even after the heading stage. In conclusion, after the heading stage, a light period shorter than the critical day length is suitable for the growth and development of rice.