Changes in the Amounts of Ribulose Bisphosphate Carboxylase Synthesized and Degraded during the Life Span of Rice Leaf (Oryza sativa L.)

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In situ synthesis and degradation of ribulose bisphosphate carboxylase (RuBPCase) were studied quantitatively in the 12th leaf blade of the rice plant during the life span of the leaf. Levels of RuBPCase protein were determined by rocket immunoelectrophoresis. The amounts of RuBPCase synthesized and degraded were estimated using ^<15>N tracer. RuBPCase was scarcely recognized in the leaf when the tip of the leaf had just emerged from the 11th leaf sheath. Then it increased rapidly and reached its maximum content a week after the completion of leaf expansion. At this time RuBPCase accounted for 56% of the soluble leaf protein N (26% of the total leaf N). The total amount of RuBPCase synthesized up to this time was about 90% of the amount synthesized throughout the leaf's life. Degradation of RuBPCase started about the time when it reached the maximum content and proceeded at a faster rate during senescence than that of the remaining soluble protein. When the leaf had senesced completely, it contained little measurable RuBPCase although the total leaf N was about 30% of the maximum level. These results clearly suggest that RuBPCase is a major N component which is used as remobilized N for the growth of young tissues. Influx and efflux of N and the synthesis and degradation of RuBPCase are discussed in relation to leaf age.
日本植物生理学会の論文