Cell-suspension cultures of two chickpea (Cicer arietinum L.) cultivars, resistant (ILC 3279) and susceptible (ILC 1929) to the fungus Ascochyta rabiei (Pass.) Lab., showed differential accumulation of the phytoalexins medicarpin and maackiain, and transient induction of related enzyme activities after application of an A. rabiei-derived elicitor. The chalcone-synthase (CHS) activity (EC 2.3.1.74) which is involved in the first part of phytoalexin biosynthesis exhibited a maximum 8–12 h after elicitation in the cells of both cultivars. Concomitant with the fivefold-higher phytoalexin accumulation, CHS activity increased twofold in the cells of the resistant cultivar. The maximum of the elicitor-induced CHS-mRNA activity was determined 4 h after onset of induction in the cultures of both cultivars, although in cells of cultivar ILC 3279 this mRNA activity was induced at a level twofold higher than that in cells of the susceptible race ILC 1929. Investigations of CHS isoenzymes by two-dimensional gel electrophoresis of immunoprecipitated in-vitro-translated protein indicated the presence of five proteins. In the cells of both cultivars only two of the isoenzymes were induced after elicitor treatment. Analysis of the total in-vitro-translated proteins by two-dimensional gel electrophoresis showed that the constitutively expressed patterns of mRNA activities in the cell cultures of the two cultivars were identical. After elicitation, considerably more translatable mRNAs were induced in the cells of cultivar ILC 3279. The few induced proteins, and their respective mRNA activities, which could be detected in the cells of the susceptible cultivar, all existed in the cells of the resistant cultivar, too. One highly induced protein (Mr 18 kDa) found in the cells of cultivar ILC 3279 reached its maximum mRNA activity 6 h after elicitor application. The amount of this protein was hardly increased in the cells of the susceptible cultivar. This protein appears to be excreted from the cells into the growth medium.

Plants possess sophisticated mechanisms to defend themselves against pathogenic microorganisms. In addition to various constitutively formed, preinfectional mechanisms, the wide range of active defence reactions is of greatest importance (Keen 1986; Collinge and Slusarenko 1987; Fritig et al. 1987). Such reactions are induced after perception of a chemical signal provided by the invading pathogen. The de novo synthesis and differential accumulation in the plant of antimicrobial phytoalexins (Bailey and Mansfield 1982) in incompatible and compatible plant — pathogen interactions play crucial roles in the specificity of host resistance (Dixon 1986; Wood 1986).

Cell suspension cultures of two chickpea (Cicer arietinum L.) cultivars, resistant and susceptible towards the chickpea pathogen Ascochyta rabiei, were compared with regard to elicitor-induced changes in phytoalexin and isoflavone accumulation. The elicitor was isolated from fermentergrown mycelium of A. rabiei and it mainly consisted of glucose, mannose and N-acetylgalactosamin. Time course and dose response studies on elicitor action demonstrated that the cell culture of the resistant cultivar ILC 3279 accumulated large amounts of the pterocarpan phytoalexins medicarpin and maackiain within 8 h. The cell culture of the susceptible cultivar ILC 1929 accumulated only small amounts of the phytoalexins some 12 h after elicitor treatment. Growth of the cell cultures and the accumulation of isoflavones and isoflavone conjugates were not altered by elicitor treatment except for a higher accumulation of formononetin 7-O-glucoside-6″-O-malonate in cell culture ILC 3279 subsequent to the maximum of phytoalexin accumulation.

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.