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Activities of NADH-Cyt c reductase and Cyt c oxidase, two enzymes involved in the electron-transport chain in plastids, mitochondria and microsomes in apple trees, Malus pumita Mill., were measured throughout the course of a year. In August, as growth and enlargement of twigs ceased, the activities of NADH-Cyt c reductase and Cyt c oxidase in organellar fractions of the living bark and flower buds began to rise. In the flower buds, the increase in the activities of the two enzymes in the mitochondrial and microsomal fractions continued until December. The levels of the two activities remained high during wintering and then the activities increased again in early April, prior to the onset of budding. In the plastid fraction the two activities continued to increase until mid-May. In the living bark, the two activities in the organellar fractions exhibited a tendency to decrease transiently in October; and thereafter they continued to increase until April. In the xylem, the activities of the two enzymes in the organellar fractions reached basal levels by late August or early September. Subsequently, the activity of NADH-Cyt c reductase did not change significantly during the winter, whereas that of Cyt c oxidase exhibited a transient increase from mid-December to early February. These changes in the living bark, xylem and flower buds were correlated with changes in the fine structures of these cells; microsomes, mitochondria and plastids in the wintering cells were more plentiful in midwinter than in summer. These results suggest that the increased activity of the electron-transport chain in winter participates not only in the metabolism required for wintering and growth in spring, but also results in an enhanced flow of electrons via the univalent pathway of reduction of oxygen that produces various species of active oxygen in the non-photosynthetic tissues.

Seasonal Variation in the Activities of NADH-Cytochrome c Reductase and Cytochrome c Oxidase in Plastids, Mitochondria and Microsomes in Apple Trees.