Ascorbate in the apoplast of elongating plant cells

Abstract

It was shown that basipetal retardation of cell elongation in the growth zone of etiolated maize mesocotyls correlates with a steep decrease in the apoplastic ascorbic acid (ASC) concentration (50 μM → 10 μM) and ascorbate redox state (17% → 5%). Exogenous ASC (0.3 mM) not only inhibits peroxidase-dependent oxidation of phenols in vitro. It also exerts a highly specific effect on the secretion of peroxidases by stimulating the release of some isoforms while inhibiting the release of others to the cell walls. This effect points to the hypothetic signaling function of apoplastic ascorbate. Previously, we described a basipetal decrease in hydrogen peroxide concentration in the apoplast (from 5.1 to 2.0 μM) and a two-times increase in cell wall peroxidase potential activity (Sharova et al., 2012). Summarizing found gradients, we can assume that the conditions in the apoplast of the upper mesocotyl segment are favorable for the occurrence of the Fenton reaction (high ASC and hydrogen peroxide concentrations) and unfavorable for the oxidation of phenols (high ASC concentration and low potential peroxidase activity), which contributes to cell wall extensibility and rapid cell elongation.