Developmental and genetic regulation of ß-glucosidase (linamarase) activity in flax seedlings

Abstract

The electrophoretic bands that represent the ß-glucosidase linamarase were used to characterize the developmental profiles for linamarase activity in germinating seedlings and young plants of two inbred types of flax (Linum usitatissimum). In flax and some other cyanogenic species, this enzyme hydrolyzes the cyanogenic compounds linamarin and lotaustralin in the penultimate step of a process that releases hydrogen cyanide. The linamarase profiles demonstrated that the activities of the four main electrophoretic bands changed in concert, and that activity changed systematically during early germination and during cotyledon expansion. In contrast, in young seedlings, linamarase activity was maintained at a constant level in the lower region of the hypocotyl and in the fully expanded cotyledons. One plant type had lower activity than the other and the plant-type difference in activity was more apparent at some developmental stages than others. The F2 progeny of crosses between the plant types demonstrated that the plant-type difference in activity, in fully expanded cotyledons, was controlled primarily by a single locus with two alleles and incomplete dominance. There were also indications of a secondary effect that was associated with plant height. The developmental and genetic regulation of flax linamarase activity are discussed in the context of findings for linamarase in other species with linamarin-based cyanogenic systems.