Localization of glyoxylate-cycle marker enzymes in peroxisomes of senescent leaves and green cotyledons

摘要

Crude particulate homogenates from leaves of barley (Hordeum vulgareL.), rice (Oryza sativaL.), leaf-beet (Beta vulgarisvar.ciclaL.) and pumpkin (Cucurbita pepoL.) cotyledons were separated on sucrose density gradients. The peroxisomal fractions appeared at a buoyant density of 1.25 g·cm−3and contained most of the activities of catalase (EC 1.11.1.6), and hydroxypyruvate reductase (EC 1.1.1.81) on the gradients. In peroxisomal fractions from detached leaves and green cotyledons incubated in permanent darkness we detected the presence of isocitrate lyase (EC 4.1.3.1) and malate synthase (EC 4.1.3.2), key enzymes of the glyoxylate cycle, andβ-oxidation activity (except in pumpkin). As proposed by H. Gut and P. Matile (1988, Planta176, 548–550) the glyoxylate cycle may be functional during leaf senescence, and the presence of two key enzymes indicates a transition from leaf peroxisome to glyoxysome; for pumpkin cotyledons in particular a double transition occurs (glyoxysome to leaf peroxisome during greening, and leaf peroxisome to glyoxysome during senesc