Changes in Aliphatic Glucosinolates Synthesis during Early Seedling Growth and Insect Herbivory in Radish (Raphanus sativus L.)

Glucosinolates, which are abundant in Brassicaceae crops as secondary metabolites, play an important role in both plant growth and self-defense. The present study was carried out to find out the temporal relationship between aliphatic glucosinolates content in tissue and level of expression of the genes involved in the biosynthesis during early seedling growth and herbivory of S. exigua in radish. The major glucosinolates found in radish were glucoraphenin in seed and glucoraphasatin in tissues other than seed. Glucoraphenin content was high in radish seeds, showing 7-fold compared to the level of glucoraphasatin, and decreased fast during germination. Glucoraphasatin in radish seedlings increased abruptly up to 7 days during germination, ranging 8.5 to 10.8 mg/g dry weight, thereafter, decreased consistently. RT-PCR study of the genes involved in the biosynthesis of glucosinolates in radish revealed that the expression of CYP79F1, CYP83A1 are gradually increased after germination, however, the glucoraphenin sharply decreased. Herbivory with S. exigua increased the amount of glucoraphasatin by 1.3 fold in all three cultivars tested.