Increase in aliphatic glucosinolates synthesis during early seedling growth and insect herbivory in radish (Raphanus sativus L.) plant

Abstract

In an effort to establish a model system to examine the biosynthesis of aliphatic glucosinolates in radish tissues, changes in the glucosinolates content and associated gene expression patterns during seed germination and feeding of beet army worms (Salix exingua) to the radish leaf tissues were investigated. Radish cultivars, 'Taebaek', 'Baekja', and 'Gwandong-yeorum', were chosen to represent the genotypes of high, intermediate, and low in their glucosinolate contents, respectively. The major glucosinolates found in radish were glucoraphenin in seeds and glucoraphasatin in young seedlings. A rapid loss in glucoraphenin content was observed immediately after seed germination along with a sharp increase in glucoraphasatin content. Partial sequences of the genes involved in the biosynthesis of glucosinolates in radish were determined using random primers manufactured based on the sequence of Brassica rapa. The RT-PCR study revealed that the expression of CYP79F1 and CYP83A1 were maintained at a high level for 14 days after germination, followed by a significant decrease, substantiating the decrease in the amount of glucosinolates. Feeding army worm on radish seedlings has resulted in an increase of the glucoraphasatin content by 1.4 folds in all three cultivars tested. Expression of CYP79F1 and CYP83A1 in the leaves were up-regulated, substantiating the increase in glucosinolates content, as compared to the control. This result suggested that there was a positive correlation between the glucosinolates contents and the expressions of CYP79F1 and CYP83A1 genes.