Elicitor-induced Changes of Enzyme Activities Related to Isoflavone and Pterocarpan Accumulation in Chickpea (Cicer arietinum L.) Cell Suspension Cultures

Abstract

The extractable activities of thirteen enzymes of primary and secondary metabolism have been measured in chickpea (Cicer arietinum L.) cell suspension cultures after treatment with an elicitor from the fungus Ascochyta rabiei (Pass.) Lab. The cell culture, derived from the A. rabiei resistant cultivar ILC 3279, constitutively accumulated the isoflavones biochanin A and formononetin together with their 7-O-glucosides and the 7-O-glucoside-6″-malonates. After elicitor application the cells rapidly form the pterocarpan phytoalexins medicarpin and maackiain. Among the enzymes of primary metabolism only the glucose 6-phosphate dehydrogenase exhibited a significant increase in activity with a maximum four hours after application of the elicitor. In phenylpropane metabolism the activities of phenylalanine ammonia lyase and chalcone synthase were enhanced by the elicitor and exhibited highest levels after four hours. In contrast the chalcone isomerase activity was not influenced by the elicitor. A substantial enhancement occurred with the isoflavone 7-O-glucosyltransferase activity eight hours after elicitor application. The results suggest that in this cell culture the elicitor-induced biosynthesis of pterocarpan phytoalexins was accompanied with a rapid and transient increase of those enzyme activities which are located at branching points of related pathways, i.e. pentose phosphate cycle, general phenylpropane metabolism, flavonoid formation and isoflavone conjugation.