Cell Type Identity in Arabidopsis Roots Is Altered by Both Ascorbic Acid-Induced Changes in the Redox Environment and the Resultant Endogenous Auxin Response

Redox plays a critical role in controlling many cellular processes of plant growth and development. To understand the effect of changes in redox on cell-type determination in the root meristem, we examined the influence of a strong reducing agent - ascorbic acid (AA) - on both the expression patterns of several cell type-specific promoters and the endogenous auxin sensitivity of auxin-responsive DR5::GUS transgenic plants. AA treatment altered the regular expression of columella-specific markers. Moreover, when the same treatment was applied to the DR5::GUS lines, normal expression of the GUS reporter was completely abolished in the auxin maximum, while exogenous auxin restored AA-driven depletion of that maximum. Interestingly, the level of DHA (dehydroascorbate, an oxidized form of AA) in the AA-treated roots was greatly increased. This indicates that changes in cell-type specificity and the sensitivity to endogenous auxin may result from an increase in the cellular DHA that is metabolized from exogenously supplied AA. Therefore, we propose that redox changes in the root meristem alter auxin homeostasis, perhaps causing a change in cell types within the root meristem.