Abstract
In the first experiment, ultrastructure of the chloroplasts was observed by an electron microscope from rice seedlings grown in controlled nursery environments under combinations of seeding density and temperature. Large amounts of starch grains were accumulated in chloroplasts of the uppermost fully expanded leaves grown under the combination of lower seeding density (9 cm2/seed) and lower temperature (25.1°C day max./11.3°C night min.), while the chloroplasts from the combination of higher seeding density (2 cm2/seed) and higher temperature (29.5°C day max./11.3°C night min.) had smaller starch grains. Chloroplasts from leaves grown under the lower seeding density and lower temperature had well-formed grana consisting of more number of overlapping thylakoids than those from the higher seeding density and higher temperature. In the second experiment, the effects of temperature and light intensity were studied on accumulation of starch grains and on formation of grana in chloroplasts of the uppermost fully expanded leaves. At the lower temperature (21.7°C day max./11.5°C night min.), increased amounts of starch grains were accumulated in the chloroplasts, but the grana were little affected by the lower temperature. Chloroplasts from leaves grown under the lower light intensity (60% shade in glasshouse) had many rudimentary grana consisting of 2-4 overlapping thylakoids. Consequently, the total number of grana thylakoids per chloroplast section was markedly reduced at the lower light intensity.
