cDNA cloning of radish (Raphanus sativus) myrosinase and tissue-specific expression in root

Two cDNA clones of myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1) we re isolated from radish (Raphanus sativus) seedlings. Both clones were iden tified as MB (B type myrosinase) from their sequence homology at the amino acid level to MBs cloned from other Brassicaceae species. The tissue distri bution of gene expression and enzyme activity of myrosinase corresponded we ll to the site of glucosinolate accumulation in different tissues of radish . The myrosinase-glucosinolate system was localized in the cotyledons in th e seedlings and in the peel of the root in the mature plant. Tissue printin g analysis showed that myrosinase mRNA and activity were localized in the e pidermis and vascular cambium that were present in the peripheral part of t he root but few signals were detected in the parenchyma inside of the vascu lar cambium, Since the myrosinase-glucosinolate system is known to be a def ense system in higher plants, the localization of the myrosinase-glucosinol ate system in the peel of the root may act to protect the sink organ from t he attack of herbivores or pathogens in soil.