Background and Aims It has previously been shown that proanthocyanidins (PAs) in the seed coat of Arabidopsis thaliana have the ability to scavenge superoxide radicals (O₂⁻). However the physiological processess in PA-deficit seeds are not clear. It is hypothesized that there exist alternative ways in PA-deficient seeds to cope with oxidative stress.

Methods The content of hydrogen peroxide (H₂O₂) and its relevance to the activities of superoxide dismutase (SOD) catalase (CAT) and peroxidases was investigated in both wild-type and PA-deficit mutant seeds. A biochemical staining approach was used to detect tissue localizations of peroxidase activities in PA-deficit mutant seeds.

Key Results PA-deficient mutants possess significantly lower levels of H₂O₂ than the wild-type despite their higher accumulation of superoxide radicals. Screening of the key antioxidant enzymes revealed that peroxidase activity was significantly over-activated in mutant seeds. This high peroxidase activity was mainly confined to the seed coat zone. Interestingly neither ascorbate peroxidase nor glutathione peroxidase just the guaiacol peroxidases (class III peroxidases) was specifically activate