Serologically-related anionic peroxidases from petunia and cucumber can substitute flavonoid antioxidants

In this study we have investigated whether naturally occurring flavonoid-de ficient mutant Red Star of Petunia hybrida is capable of metabolizing H2O2 by invoking other antioxidant enzyme system. We demonstrated that reduced f lower pigmentation due to a reduction in the chalcone synthase mRNA express ion results in strong H2O2 accumulation accompanied by the induction of a s pecific set of anionic peroxidase (PRX), serologically-related to main cucu mber srPRX. We found correlation between rate of H2O2 accumulation and qual itative, as well as quantitative changes in the srPRX expression which seem s to be determined by flower phenotype. In detached flower buds cultured in vitro both abscisic acid and anther extirpation prevented anthocyanin pigm entation, and thus flavonoid biosynthesis, resulting in a marked accumulati on of immunoprecipitable srPRX. In contrast, pigmented flowers cultivated u nder the same conditions did not accumulate corresponding srPRX. The result s suggest that a specific set of anionic PRX can substitute for the absence of flavonoid antioxidants.