| Abstract: | Plant growth, leaf protein and chlorophyll content, and chloroplastultrastructure as affected by nitrogen (N) were examined infour rice (Oryza sativa L.) cultivars grown in culture solutionunder controlled conditions. Increasing N concentration generallyincreased height and shoot dry weight of all cultivars. Cultivardifferences were significant at normal N level (40 ppm). Amongcultivars, IR8 was most responsive to increasing N, having thesignificantly highest shoot dry weight and protein content.Total chlorophyll and protein contents varied with cultivarand N, but chlorophyll a/b ratio remained constant. At the ultrastructurallevel, chloroplasts had generally well-developed grana and stromalamellae at 40 ppm.N. Chloroplasts at high N had from one tofour times as many grana as the N-deficient chloroplasts. Nitrogendeficiency reduced the size of the chloroplast, grana-stromalamellae and resulted in fewer poorly stacked grana. Increasingthe N level (120 ppm) above the normal level did not significantlyaffect chloroplast size of any cultivar, except for IR8 whichhad the largest chloroplast. A reduction in the number of starchgrains was observed in IR8, but more were present in ER36 underN-deficient conditions. The size of starch grains was not affectedby N and did not differ among cultivars. Plastoglobuli appearedto be larger under N-deficient conditions. Nitrogen had no effecton the number of plastoglobuli but cultivar differences existed.The highly N-responsive IR8 (based on dry weight) had the largestchloroplast which increased with N level. The increase in chloroplastsize accounted for the increase in both chlorophyll and proteincontents and, consequently, dry weight. Key words: Oryza sativa L., chloroplast, chlorophyll, protein |
