The presence of dehydroascorbate and dehydroascorbate reductase in plant tissues

作者：Christine Helen Foyer, Philip M. Mullineaux · 发表于：FEBS Letters · 年份：1998 · DOI：10.1016/s0014-5793(98)00281-6 · 被引用次数：90 · 研究领域：Plant Stress Responses and Tolerance、Photosynthetic Processes and Mechanisms、Plant Micronutrient Interactions and Effects

Ascorbate, an essential antioxidant in plant tissues, is oxidised to dehydroascorbate (DHA) via successive reversible single electron transfers with monodehydroascorbate (MDHA) as a free radical intermediate. Rapid regeneration of ascorbate from its oxidised forms is required to support antioxidant capacity. MDHA radicals have a relatively short lifetime and disproportionate at neutral pH values and above to DHA and ascorbate. MDHA radicals can be reduced directly to ascorbate by reduced ferredoxin and by NAD(P)H-dependent monodehydroascorbate reductases, which are found in several cellular locations. DHA can be reduced directly by reduced glutathione at alkaline pH values and also by enzymes which catalyse this conversion (dehydroascorbate reductases, DHAR). It has recently been argued that DHA detected in chloroplast extracts is artefactual, that in vivo DHA levels are negligible and that this metabolite is formed purely artefactually during extraction of plant tissues [1]. This hypothesis was largely based on the observation that, at concentrations thought to exist in the chloroplast, DHA could cause oxidative inactivation of two enzymes known to be regulated by the thioredoxin system [1]. The authors therefore concluded that DHA accumulation must be avoided [1]. This conclusion is erroneous, however, since it does not take into account the dynamic nature of the regulation of the thiol-mediated enzymes of the chloroplasts. It is well established that the stromal enzymes re...