REDOX STATE OF ASCORBIC-ACID IN THE APOPLAST OF STEMS OF KALANCHOE-DAIGREMONTIANA

The aqueous phase of cell walls in stems of Kalanchoe daigremontiana H amet et Perrier de la Bathie (apoplast) contained ascorbic acid (AA) a nd dehydroascorbic acid (DHA). Ratios of AA/(AA + DHA) were 0.31 +/- 0 .12 (so: n=4), whereas those of whole stems (tissues plus apoplast) we re > 0.9. The amounts of (AA + DHA) in the stems were 1 970 +/- 190 (s o, n=4) nmol g(-1) fresh weight and those in the apoplast were 14 +/- 2 (so, n=4) nmol g(-1) fresh weight of stems. Ratios of AAI(AA + DHA) differed in different tissues of the stems. The ratios of AAI(AA + DHA ) of apoplast plus symplast were in the following order: pith similar or equal to epidermis plus cortex > vascular bundle system, and those of apoplast were: pith > epidermis plus cortex > vascular bundle syste m. Ratios of AA/(AA + DHA) In the apoplast of the different tissues de creased to about 1/3 of the original values after wounding, while the amounts of (AA + DHA) remained largely unaffected. In contrast, solubl e apoplastic peroxidase activities increased 30- to 70-fold on woundin g. Hydrogen peroxide infiltrated into stems caused a rapid oxidation o f AA. Coniferyl alcohol was oxidized by peroxidase in intercellular wa shing fluid and by cell wall-bound peroxidase. The oxidation of conife ryl alcohol by peroxidase in intercellular washing fluid was completel y inhibited as long as AA was present in reaction mixtures. The oxidat ion of the coniferyl alcohol by cell wall-bound peroxidase was partial ly inihibited by AA and the degree of inhibition was dependent upon th e concentration of AA. The possible functions of AA in the apoplast ar e discussed in relation to the control of peroxidase-dependent oxidati on of phenolics.