Localized increases of polyphenol concentration and antioxidant capacity in relation to the differential accumulations of copper and cadmium in roots and in shoots of sunflower

Abstract

In this study, we examined the relevance of polyphenols in the response of sunflower plants to acute Cu and Cd stresses. More specifically, we aimed to correlate spatially and temporally the accumulation of polyphenols with the occurrence of oxidative stress, and to estimate their contribution to the antioxidant capacities. Under our experimental conditions, the presence of Cu and Cd (75 µmol·L–1) in the nutrient solution caused oxidative damage, as detected by the accumulation of malondialdehyde, in roots of Cu-treated plants and in leaves of Cd-treated plants; in the latter, significant inhibition of photosynthesis also occurred. These effects were in agreement with the preferential accumulation of Cu in the roots and the greater translocation of Cd to the shoots. This oxidative damage was associated with a concerted plant response, characterized by stimulation of phenylalanine ammonia-lyase, ascorbate peroxidase, and guaiacol peroxidase activities, and by the accumulation of polyphenols whose concentrations were closely correlated (R2 = 0.95) to the total antioxidant capacity of plants extracts. Globally, the co-occurrence of oxidative damages and polyphenol accumulation, and the correlations among polyphenol concentrations, total antioxidant capacities, and stimulations of the peroxidases support the involvement of polyphenols in protection against oxidative damage generated by Cu and Cd in plants.