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.
Highlights
The fast growth of plants is achieved by the mechanism of cell extension growth
We found only a few publications in which the concentration and redox state of ascorbate in the apoplast were examined in the context of shoot extension growth
In the apoplast of pine hypocotyls, the average sum of ASC + didehydroascorbic acid (DHA) was low, approximately 10 μM (1–4 nmol/g FW, 0.2–0.4 ml of apolastic fluid was extracted from 1 g fresh wt by infiltration/centrifugation technique), redox state was high, approximately 75% (Sanchez et al, 1997)
Summary
The fast growth of plants is achieved by the mechanism of cell extension growth. At the extension stage, which lasts from several hours to several days, plant cells osmotically absorb water, form a central vacuole with a high concentration of osmotically active substances, and hugely increase in size. Over the long history of growth investigation, it has been firmly established that regulation of growth rate mainly occurs through modifications in cell walls’ extensibility. Metabolism of cell walls is strongly dependent on continuous secretion of proteins, polysaccharides, sugars, organic and amino acids, and various phenolic compounds. Many of these compounds participate in hydrolytic and oxidative reactions. Some of these reactions make it possible to rapidly increase (or decrease) wall extensibility and rapidly accelerate (or decelerate) cell extension (Sharova, 2004)
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