Effects of sulfate application and shading on myrosinase activity and S-methyl-L-cysteine sulfoxide content in radish (Raphanus sativus L.) roots

Abstract

Myrosinase (thioglucoside glucohydrolase, EC 3. 2. 3. 1) in radish roots is an enzyme catalyzing formation of volatile 4-methylthio-3-butenyl isothiocyanate (MTB-ITC) from 4-methylthio-3-butenyl glucosinolate (MTB glucosinolate). S-Methyl-L-cysteine sulfoxide (SMCS) is a precursor of MTB glucosinolate. The amount of MTB-ITC is one of the factors evaluating the quality of radish roots. We examined effects of sulfate application and shading on the myrosinase activity and SMCS content in the radish roots. It is suggested that radish roots contained enough amounts of myrosinase to yield MTB-ITC from the MTB glucosinolate, although shading decreased the activity. On the other hand, SMCS content in the roots increased with an increasing sulfate application and by shading. Therefore, it is presumed that sulfate application and shading contribute to MTB-ITC formation through an increase in SMCS content.