Distribution of β-Thioglucosidase Activity in Intact Plants, Cell and Tissue 6Brassica napus L.

Abstract

Distribution of myrosinase activity in extracts from seeds, intact plants, cell cultures and regenerated callus and plants of Brassica napus L. was determined by the rate of glucose formation from glucosinolate hydrolysis. Calli with shoots and regenerated plants were obtained from protoplasts or from explants. Of the seedling organs from Brassica napus L. cv. Niklas, hypocotyls showed the highest myrosinase activity. In cotyledons a nearly constant enzyme activity was determined over the first 6 d, followed by a gradual decline. Roots showed a fast decline in enzyme activity over the investigated period. Freshly-isolated protoplasts contained less myrosinase activity than the original intact tissue. The enzyme activity in developing calli generally decreased during the first culture periods. After the initial decline a low activity was found which was stable for a period of more than 2 years. The enzyme activity showed fluctuations when measured at different times after medium change. Protoplast calli with regenerated shoots showed a considerably higher myrosinase activity than calli without shoots. Myrosinase activity was also found in explant calli including explant calli from cotyledons and hypocotyls after induction of shoots. Myrosinase activity in seeds from 21 cultivars of Brassica napus, Brassica campestris, Sinapis alba and Raphanus sativus was tested and the highest myrosinase activity was found in seeds from the Sinapis alba cultivar Trico while the lowest activity was found in the Brassica campestris cultivar Rapido III. Leaf, stem and inflorescence from flowering regenerated or seed-grown plants contained a low but significant myrosinase activity. In contrast, roots showed a high myrosinase activity. The results obtained from regenerated plants indicate that the myrosinase system is stable in vitro culture, and that the glucosinolate-myrosinase system is active in calli tissue.