Changing Activities During Senescence and Sites of Synthesis of Photosynthetic Enzymes in Leaves of the Labiate,Perilla frutescens(L.) Britt.

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Abstract
The changing activities of several regulatory enzymes of the photosynthetic carbon reduction cycle accompanying ageing of the third leaf pair of Perilla frutescens fall into two distinct categories: firstly, enzymes which reach maximum activity prior to the completion of leaf expansion followed by a rapid decline (phosphoribulokinase, ribulose-l,5-diphosphate carboxylase, and NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase); secondly, enzymes which maintain high activity beyond completion of leaf expansion and decline only at a late stage in senescence (phosphoglycerate kinase, NADH-linked glyceraldehyde-3-phosphate dehydrogenase, alkaline fructose-1,6-diphosphatase, and ribose-5-phosphate isomerase). The introduction of the ribosomal inhibitors D-threo chloramphenicol, lincomycin, D-2-(4-methyl-2,6-dinitroanilino)-N-methyl propionamide, and cycloheximide to illuminated, detached shoot systems of 2-d-darkened Perilla plants has suggested that synthesis of ribulose diphosphate carboxylase, NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase, and possibly phosphoribulokinase, is mediated by 70 S-based chloroplastic ribosomes. A chloroplastic site of synthesis of these three photosynthetic enzymes is consistent with their early deterioration during leaf ageing.

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