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Redox state of ascorbic acid in the apoplast of stems of Kalanchoë daigremontiana

1993; Wiley; Volume: 89; Issue: 4 Linguagem: Inglês

10.1111/j.1399-3054.1993.tb05286.x

1399-3054

Umeo Takahama,

Natural product bioactivities and synthesis

The aqueous phase of cell walls in stems of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie (apoplast) contained ascorbic acid (AA) and dehydroascorbic acid (DHA). Ratios of AA/(AA + DHA) were 0.31 ± 0.12 (SD, n = 4), whereas those of whole stems (tissues plus apoplast) were >0.9. The amounts of (AA + DHA) in the stems were 1970 ± 190 (SD, n = 4) nmol g −1 fresh weight and those in the apoplast were 14 ± 2 (SD, n = 4) nmol g −1 fresh weight of stems. Ratios of AA/(AA + DHA) differed in different tissues of the stems. The ratios of AA/(AA + DHA) of apoplast plus symplast were in the following order: pith ⋍ epidermis plus cortex > vascular bundle system, and those of apoplast were: pith > epidermis plus cortex > vascular bundle system. Ratios of AA/(AA + DHA) in the apoplast of the different tissues decreased to about 1/3 of the original values after wounding, while the amounts of (AA + DHA) remained largely unaffected. In contrast, soluble apoplastic peroxidase activities increased 30‐ to 70‐fold on wounding. Hydrogen peroxide infiltrated into stems caused a rapid oxidation of AA. Coniferyl alcohol was oxidized by peroxidase in intercellular washing fluid and by cell wall‐bound peroxidase. The oxidation of coniferyl alcohol by peroxidase in intercellular washing fluid was completely inhibited as long as AA was present in reaction mixtures. The oxidation of the coniferyl alcohol by cell wall‐bound peroxidase was partially inihibited by AA and the degree of inhibition was dependent upon the concentration of AA. The possible functions of AA in the apoplast are discussed in relation to the control of peroxidase‐dependent oxidation of phenolics.