Tolerance of Arabidopsis thaliana to the Allelochemical Protocatechualdehyde

We investigated the effects of the secondary metabolite protocatechualdehyde (PCA, 3,4-dihydroxybenzaldehyde) on stress markers, including fluorescence parameters and the concentrations of pigments, free radicals, protein, and lipid peroxides, in adult plants of Arabidopsis thaliana. The content of proline, carotenoids, and chlorophylls a and b peaked 9?h after administration of 3?mM PCA (the highest concentration used in this study), although malonyldialdehyde and dry mass contents peaked 24?h following PCA treatment. Leaf staining revealed peak production of O₂ ^? between 30 and 90?min post-treatment and peak production of H₂O₂ between 1 and 9?h post-treatment. Several effects, including the observed furling of leaf margins (leaf rolling), the increases in proline content and dry to fresh weight ratio, and the oxidative burst, are reminiscent of the plant response to drought. Early dehydration in PCA-treated plants was confirmed by decreases in leaf water potential, relative water content, and stomatal opening in the first hours of treatment. Thus, PCA seems to be either inducing water deficiency stress (probably through action in the roots) or directly triggering antidrought defenses. In either case, plants showed tolerance to the concentrations employed in this study, with most of the parameters observed having recovered control values within a week of treatment.