ELICITOR-INDUCED METABOLIC CHANGES IN CELL-CULTURES OF CHICKPEA (CICER-ARIETINUM L) CULTIVARS RESISTANT AND SUSCEPTIBLE TO ASCOCHYTA-RABIEI .1. INVESTIGATIONS OF ENZYME-ACTIVITIES INVOLVED IN ISOFLAVONE AND PTEROCARPAN PHYTOALEXIN BIOSYNTHESIS

Cell-suspension cultures of Ascochyta rabiei-resistant (ILC 3279) and -susceptible (ILC 1929) chickpea (Cicer arietinum L.) cultivars were compared with regard to their elicitor-induced accumulation of pterocarpan phytoalexins and increases in the activities of biosynthetic enzymes. The growth performances and protein patterns of the two cell-culture lines were essentially identical. Treatment of cell cultures with a polysaccharide elicitor from A. rabiei induced fivefold-higher amounts of the phytoalexins medicarpin and maackiain in the cells of the resistant than in the susceptible cultivar. Glucose 6-phosphate dehydrogenase and eight enzymes representing the general phenylpropanoid pathway, the flavonoid-forming steps and the pterocarpanspecific branch of phytoalexin biosynthesis were found to be elicitor-induced. Phenylalanine ammonia-lyase and chalcone synthase reached sharp, transient optima some 8 h after elicitor application in the cells of both cultivars. The activities of isoflavone 2′- and 3′-hydroxylases were only induced in cells of the resistant cultivar with a maximum after 8 h. Cinnamic acid 4-hydroxylase, chalcone isomerase, 2′-hydroxyisoflavone reductase and pterocarpan synthase showed a later or no sharp optimum. The isoflavone-specific 7-O-glucosyltransferase was not induced in either cell-culture line. Cells of the susceptible cultivar failed to induce significant activities of isoflavone 2′-hydroxylase and these cells produced only very low amounts of phytoalexins. Isoflavone 2′-hydroxylase is postulated to be the main limiting enzyme for pterocarpan biosynthesis in cells of the susceptible cultivar. The pterocarpan biosynthetic pathway in chickpea cells represents a suitable model for investigations of differential gene activation in connection with the expression of antimicrobial defence reactions. © 1990 Springer-Verlag.