CULTIVAR DIFFERENCES IN GROWTH AND CHLOROPLAST ULTRASTRUCTURE IN RICEAS AFFECTED BY NITROGEN

Plant growth, leaf protein and chlorophyll content, and chloroplast ul trastructure as affected by nitrogen (N) were examined in four rice (O ryza sativa L.) cultivars grown in culture solution under controlled c onditions. Increasing N concentration generally increased height and s hoot dry weight of all cultivars. Cultivar differences were significan t at normal N level (40 ppm). Among cultivars, IR8 was most responsive to increasing N, having the significantly highest shoot dry weight an d protein content. Total chlorophyll and protein contents varied with cultivar and N, but chlorophyll a/b ratio remained constant. At the ul trastructural level, chloroplasts had generally well-developed grana a nd stroma lamellae at 40 ppm N. Chloroplasts at high N had from one to four times as many grana as the N-deficient chloroplasts. Nitrogen de ficiency reduced the size of the chloroplast, grana-stroma lamellae an d resulted in fewer poorly stacked grana. Increasing the N level (120 ppm) above the normal level did not significantly affect chloroplast s ize of any cultivar, except for IR8 which had the largest chloroplast. A reduction in the number of starch grains was observed in IR8, but m ore were present in IR36 under N-deficient conditions. The size of sta rch grains was not affected by N and did not differ among cultivars. P lastoglobuli appeared to be larger under N-deficient conditions. Nitro gen had no effect on the number of plastoglobuli but cultivar differen ces existed. The highly N-responsive IR8 (based on dry weight) had the largest chloroplast which increased with N level. The increase in chl oroplast size accounted for the increase in both chlorophyll and prote in contents and, consequently, dry weight.