β-Glucosidases potentially involved in cyanogenesis during infection of white clover by Stemphylium sarciniforme

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Abstract
White clover (Trifolium repens L.) and Stemphylium sarciniforme (Cav.) Wilt. each produced a β-glucosidase which hydrolyzed linamarin and cyanogenic glucosides in crude extracts of white clover. The relative activities of these β-glucosidases were determined at 0, 48, and 96 h after inoculation of three white clover selections that differed in the presence or absence of cyanogenic β-glucosides (G) and β-glucosidase (E), i.e., G+E+, G+E−, and G−E−. The β-glucosidase from white clover precipitated from aqueous solution at 50% saturation with ammonium sulfate was cationic at pH 5.0 and had equal activity on linamarin and amygdalin. The β-glucosidase from S. sarciniforme precipitated from solution at 75% saturation with ammonium sulfate was anionic at pH 7.1 and was three times more active on amygdalin than on linamarin. The amount of host β-glucosidase activity in the G+E+ white clover inoculated with S. sarciniforme decreased 39% in the interval 48 to 96 h. β-Glucosidase with activity on white clover substrates was not extracted from either the G+E− or G−E− selections before or after inoculation. Pathogen β-glucosidase was detected first in all selections at 48 h and had increased by 96 h to 160, 290, and 260%, respectively, in the G+E+, G+E−, and G−E− selections.