Short- and long-term effects of dehydroascorbate in Lupinus albus and Allium cepa roots

Administration of I mM dehydroascorbate (DHA) results in a rapid and large increase in cellular ascorbate (AA) content in both Lupinus albus L. and Al lium cepa L. root tips. Uptake of DHA from the medium occurs at a high rate within 10-12 h of incubation, and is slowed down thereafter. In the first few h, DHA reduction to AA is apparently correlated to GSH depletion and sl ightly higher DHA reductase activity. DHA incubation also seems to induce n ew GSH synthesis. Longer DHA incubation (24 h) affects root growth by inhib iting cell proliferation. At this stage, an apparently generalised oxidatio n of SH-containing proteins is observed in DHA-treated roots. Treatment wit h I MM L-galactono-gamma -lactone, the last precursor of AA biosynthesis, r esults in an increase in AA content similar to that obtained with DHA, but stimulates growth and affects the redox state of SH-containing proteins in the opposite way. A possible multi-step mechanism of DHA reduction/removal is suggested and the hypothesis that DHA inhibits cell cycle progression by affecting the redox state of SH-containing proteins is discussed.