Increase in Enzyme Activities Related to Ascorbate Metabolism during Cold Acclimation in Poplar Twigs<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>

Abstract

Activities of ascorbate free radical reductase, ascorbate peroxidase, dehydroascorbate reductase, ascorbate oxidase and catalase in the twigs of poplar, Populus gelrica, were measured throughout a year. Activity levels of the first three enzymes were high during the wintering period of the life cycle, and the changes in the three enzyme activities occurred simultaneously. In fall, when the growth and enlargement of the tissues began to cease, the activities began to increase. In contrast to the activities of the above three enzymes, catalase activity began to increase as the growth and enlargement proceeded, and the activity dropped by early November. Ascorbate levels in the twigs were measured, and the living bark and the xylem tissue were found to contain similar levels of ascorbate (8 to 20 μmol and 2 to 14 μmol per gram dry weight, respectively). From these results, it was suggested that in the growing period, deleterious H2O2 produced in such organelles as the endoplasmic reticulum is decomposed by catalase, and that in winter, oxidation and reduction reactions of ascorbate function not only to detoxify the peroxide produced in the tissues, but also serve as a respiratory process to regenerate NADPH in the non-photosynthetic tissues of perennials.