Abstract
Vacuoles and leucoplasts were isolated from red beet (Beta vulgaris L.) taproots and compared in terms of ascorbic acid concentration and ascorbate oxidase (AO) activity. The total amount of ascorbic acid (AAtot) was greater in vacuoles than in the plastids. The content of oxidized form of ascorbic acid, i.e., dehydroascorbic acid (DHA), was also higher in vacuoles than in the leucoplasts. However, the content ratios of reduced ascorbic acid (AA) to its oxidized form (AA : DHA) were similar in vacuoles and leucoplasts. The studied organelles displayed a relatively high AO activity. The oxidation of AA was catalyzed by ascorbate oxidase in vacuoles, whereas it was mediated by ascorbate oxidase and polyphenol oxidase in leucoplasts. The oxidases catalyzing AA oxidation are presumed to regulate the redox state of ascorbic acid in these organelles.
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