Glucose Oxidase, a Potential Contributor towards Flower Colour Modification in the Capitula of Carthamus tinctorius L.

Abstract

Experiments were performed to demonstrate that glucose oxidase from Aspergillus niger conduces towards the flower colour modification in the capitula of Carthamus tinctorius L. For inducing the catalytic reaction, glucose oxidase displayed the absolute requirement for precarthamin, (β-D-glucose and atmospheric oxygen. The enzyme alone could also react with precarthamin to produce carthamin, however, the magnitude is very weak. No activity appeared in the reaction medium containing heat-inactivated enzyme sample even after the addition of glucose. The evidence was further corroborated in an incubation model, in which hydrogen peroxide and precarthamin is co-existent, instead of being added the enzyme and its substrate. The experimental model system showed a quite similar reaction pattern to that of the enzymatic process, indicating that a concomitant weight of red carthamin is accumulated as a major product of the hydrogen peroxide catalysis. On the basis of these assays, it was postulated that glucose oxidase may participate indirectly in the carthamin formation via the process of generating its by-product, hydrogen peroxide, which could react directly with precarthamin. The data are discussed in relation to flower colour modification induced characteristically in C. tinctorius capitula.