Regulation of POD activity by pelargonidin during vegetative growth in radish (Raphanus sativus L.)

• POD activities were higher in the tissues containing more pelargonidin in three radish cultivars.
• Significant positive correlations were observed between POD activity and pelargonidin content during the growth of three radish cultivars.
• The expression levels of anthocyanin biosynthesis genes were constitutive in the flesh but decreased in the skin during the growth of Man Tang Hong radish.
• The expression kinetics of POD gene Rsprx1 was similar to those of anthocyanin biosynthesis genes in Man Tang Hong radish.

Peroxidase (POD) can degrade anthocyanin in planta. Either positive or negative correlation between POD activity and anthocyanin content has been reported in plants. Given the occurrence of conflicting results, we investigated the relationship between POD activity and anthocyanin content during vegetative growth of three radish (Raphanus sativus L.) cultivars (Man Tang Hong, Da Hong Pao and Si Ji Da Gen). Significant positive correlations were observed between POD activity and pelargonidin content in the flesh throughout the vegetative growth stage and in the skin from 50 to 90 days after sowing in all three cultivars. A high-level constitutive expression of genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS) directly involved in anthocyanin biosynthesis was observed in the flesh, while, the expression of these genes was decreased in the skin with the growth of cultivar Man Tang Hong. The expression of anthocyanin biosynthesis genes requires coordinated transcripts of a bHLH transcription factor, Transparent Testa 8 (RsTT8), and a MYB transcription factor. RsMYB was mainly expressed in the flesh of Man Tang Hong, while RsTT8 was expressed in both the skin and flesh of Man Tang Hong. The expression kinetics of POD gene Rsprx1 was similar to those of anthocyanin biosynthesis genes in Man Tang Hong during growth. These results indicated that the activity and expression of POD can be regulated by anthocyanin content in the plant during development.