Relation between Nitrogen and Ribulose-1,5-bisphosphate Carboxylase in Rice Leaves from Emergence through Senescence

The relation between N content and ribulose-l,5-bisphosphate (RuBP) carboxylase protein was examined in the 12th leaf blade of rice. Plants were grown under different amounts of N after the emergence of the 12th leaf blade. RuBP carboxylase protein increased with leaf N during leaf expansion. The synthesis of RuBP carboxylase predominated during this period, and changes in the amounts of carboxylase synthesized until leaf death paralleled changes in the N influx to the leaves. When the carboxylase reached its maximum content, the proportion of RuBP carboxylase to leaf N was 27 to 28% irrespective of N treatment. As the leaf senesced, however, this proportion differed significantly with the treatment. It was higher in the N-deficient leaf than in the N-sufficient leaf. This was due to different patterns of RuBP carboxylase degradation for the treatments during senescence. RuBP carboxylase was degraded actively during the early stage of senescence in the N-sufficient leaf, whereas its degradation proceeded almost constantly in the N-deficient leaf during senescence.