Partitioning of Absorbed Nitrogen to Chloroplast, Soluble Protein and Rubisco in Rice Leaves under Low Nitrogen Supply

Nitrogen (N) fractions such as chloroplast, total soluble protein and ribulose-1, 5-bisphosphate carboxylase (Rubisco) in rice leaves were determined for 8 cultivars of indica rice at two N supply levels. The conversion rates from absorbed N to chloroplast-N ranged from 78 to 84%, and the rates depended not on the exogenous N levels but on the cultivars. The amounts of total soluble protein and Rubisco increased linearly with increasing leaf N content, and their correlation coefficients were significantly high. The proportion of total soluble protein-N to total leaf N was different among cultivars, and their values varied from 59 to 75% in the control plot and from 43 to 61% in the low N plot. The Rubisco-N accounted for about 24 to 45% of total leaf N in the control plot and varied from only 5.8 to 27% in the low N plot depending on cultivars. The partitioning rate of total leaf N to the Rubisco-N was influenced most severely by low N supply among the N fractions examined.