Hydrolysis of Conjugated Gibberellins by β-Glucosidases from Dwarf Rice ( Oryza sativa L. cv. «Tan-ginbozu»)

Abstract

Dwarf rice (Oryza sativa L. cv. «Tan-ginbozu») is widely used for gibberellin conjugate bioassay. Soluble and particulate fractions from seeds and seedlings of this variety showed hydrolytic activity toward [(3)H]GA-O-Glc. The soluble fraction from mature seeds exhibited the highest [(3)H]GA-O-Glc/pNP-β-Glc hydrolysis ratio which decreased during the early germination phase. The soluble β-glucosidases from mature seeds were efficiently separated by CMSephadex C-50 column chromatography. It was found that the most active β-glucosidase CM 1 from seeds hydrolyses GA(8)-O-2-Glc 8 times faster than GA(3)-O-3-Glc and GA(3) Glc ester. In shoots of 4-d-old etiolated seedlings a soluble β-glucosidase (CM 4) is present which showed a 200 times faster hydrolysis of GA(8)-O-2-Glc as compared to GA(3)-O-3-Glc. Both the β-glucosidase CM 4 and the main β-glucosidase component CM 5 possessed relatively high GA(3) Glc ester hydrolysing activity. Our enzymatic findings demonstrate that in dwarf rice bioassay (leaf application) the GA-OGlc with equatorially arranged glucosyl residues (O-2-glucosides of GA(8), GA(26), GA(27), and GA(29)) and GA Glc esters are hydrolysed by the concerted action of the endogenous a-glucosidases CM 4 and CM 5 from shoots.