The leaf carbon and nitrogen metabolism characteristics and their relationships with nitrogen utilization efficiency(NUE) at jointing stage were investigated with Xiuhui 2 (low NUE), R8312 (medium NUE) and Wuyou 244 (high NUE) as materials under the lower nitrogen level (58 mg/kg). The results showed that the contents of sucrose and soluble sugar in the leaves of different rice genotypes were Wuyou 244 > R8312 > Xiuhui 2, the ratio of starch content to soluble sugar content and the ratio of starch content to sucrose content were Xiuhui 2>R8312>Wuyou 244, significantily differed among genotypes. The starch content and the ratio of sucrose content to soluble sugar content were not genotypically specific. The total nitrogen content (TNC), protein nitrogen content (PNC), PNC/TNC, RC(Rubisco content)/PNC and RC/TNC in the leaves of different rice genotypes exhibited significant differences, showing an increasing trend of Wuyou 244 < R8312 < Xiuhui 2 for the former two indices and a trend of Xiuhui 2>R8312>Wuyou 244 for the latter three; RC was not genotypicallyspecific. The contents of chlorophyll and carotenoid, activity of PSⅡ, carboxylation efficiency, activities of carbonic anhydrase, acid invertase and sucrose phosphate synthase in the leaves of Wuyou 244 with high NUE were significantly higher than those of the other genotypes. The activities of nitrate reductase, glutamine synthetase and glutamate synthase and glutamate dehydrogenase in the leaves of Wuyou 244 with high NUE were also significantly higher than those of the other genotypes. Statistical analyses indicated that the leaves of rice genotype with high NUE had the distinguished characteristics of higher soluble sugar content, sucrose content, RC/TNC and RC/PNC, their physiological base were higher glutamine synthetase activity and primary PSⅡ activity.
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