Abstract
Lowland rice plants (Norin-17) of early and sermi-late cultivations, and the ears of the same variety of late cultivation were treated during night time with high (30°C) and low (20°C) temperature (15°C -30°C for the ear treatment) for certain periods in various stages of kernel development. Investigations on maturation, fruiting and specific gravities of the seeds, and some microscopic observations on bran layer and starchy tissue of the kernels were conducted. The results are summmarized as follows: 1) High night temp. accelerated the kernel development and maturation. 2) Chalky kernels and partially-chalky kernels markedly occured in the plots of high night temp. around 1O days after flowering. That was presumably due to an unbalance in supply and demand of nutrients, and to increased consumption of storage foods in the weak kernels, which were caused by high temp. 3) Both high and low night temp. 5 to 15 days after flowering caused milky-white kernels which considered to be due to the temporary hindrance of ripening. Many of milky-white kernels due to hindrance in early ripening stages had an opaque part (white-core-like but different from that of white-core kernel in shape and location) in their tissues. 4) Measurements on specific gravities of paddy, brown rice and parts of kernel revealed insufficiency of storage matter accumulation in the outer parts of kernel under high night temp. conditions. But as for the inner parts, they had larger s.g. values than those from low temp. plots, indicating good accumulation in these parts in earlier stages of seed development. 5) High night temp. in early stages of seed growth increased aleurone cells and thickness of bran layer on back side of kernel. Low temp. decreased these measurements. 6) On the cross sections of kernels from high night temp. plots a well-ar-ranged radial starch tissue (characteristic of Koshitsu-Mai) was observed. 0n the other hand, remarkable development of flatish cells along the dorso-ventral diameter of kernel (typical for Nanshitsu-Mai) was noticed in the kernels from low night temp. plots
