Development of Enzymes of the Glyoxylate Cycle during Senescence of Pumpkin Cotyledons

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The presence and activities of isocitrate lyase (EC 4.1.3.1) and malate synthase (EC 4.1.3.2) were studied during senescence of pumpkin cotyledons (Cucurbita sp. Amakuri Nankin). After incubation of detached cotyledons in permanent darkness, the activities appeared and increased up to the eighth day and then declined, while the activities of catalase (EC 1.11.1.6), glycolate oxidase (EC 1.1.3.1), and hydroxypyruvate reductase (EC 1.1.1.81) decreased dramatically. After fractionation of cell organelles by sucrose density gradient, we detected isocitrate lyase and malate synthase activities in peroxisomal fractions. The activity of the two key enzymes of the glyoxylate cycle also increased during senescence in vivo and we confirmed the presence of the two enzymes in the peroxisomal fractions after sucrose gradient centrifugation. At every point examined, the level of malate synthase was demonstrated by immunoblotting. It is concluded that the development of isocitrate lyase and malate synthase activities represents the transition from leaf peroxisomes to glyoxysomes and that such a phenomenon is associated with senescence.
日本植物生理学会の論文