Comparative investigations of the glucosinolate-myrosinase system in Arabidopsis suspension cells and hypocotyls.

Glucosinolates are secondary metabolites derived from amino acids. Upon hydrolysis by myrosinases, they produce a variety of biologically active compounds. In this study, the glucosinolate-myrosinase system was characterized in Arabidopsis suspension cells. A total of seven glucosinolates were identified and the myrosinase activity was determined. Plant suspension cells have been used as model systems in many areas of study. To investigate whether the glucosinolate-myrosinase system in suspension cells works similarly to that in planta, 10-day-old seedling hypocotyls were used for comparative studies. A total of 16 glucosinolates were identified in hypocotyls. The two types of samples were also treated with methyljasmonate (MeJA)--a signaling compound induced by herbivore attack and wounding to initiate plant defense processes. The glucosinolate levels and their responses to MeJA varied greatly with the age of the cells. Two-day-old cells were most responsive, with the levels of all seven glucosinolates induced by MeJA, while in 4-day-old cells only the levels of indole glucosinolates were increased. In hypocotyls, the levels of indole glucosinolates and aliphatic glucosinolates (especially 4-methylsulfinylbutyl- and 8-methylsulfinyloctylglucosinolates) were significantly increased by MeJA treatment. The transcript levels of several genes involved in glucosinolate biosynthesis were induced in both suspension cells and hypocotyls after MeJA treatment. Myrosinase levels and activities were also monitored. The molecular bases underlying the differences of glucosinolate metabolism in the suspension cells and hypocotyls were discussed.