Elicitation and Suppression of Phytoalexin and Isoflavone Accumulation in Cotyledons of Cicer arietinum L. as Caused by Wounding and by Polymeric Components from the Fungus Ascochyta rabiei

Abstract

Shortly after sowing cotyledons of chickpea (Cicer arietinum) start to accumulate the isoflavones biochanin A and formononetin together with their 7‐0‐glucosides and their 7‐0‐glucoside‐6″‐malonates. The additional accumulation of the pterocarpan phytoalexins medicarpin and maackiain can be induced by wounding of the cotyledons. Treatment of sliced cotyledons with a crude elicitor fraction obtained from the growth medium or the mycelium of the chickpea pathogenic fungus Ascochyta rabiei (Pass.) Lab. leads to a dramatic increase in the level of numerous aromatic compounds, especially of the isoflavone aglyca and the phytoalexins. Accumulation of isoflavone conjugates is not altered by elicitor treatment as shown by time course studies, and dose‐response curves. A protein preparation (“suppressor”) isolated from the culture filtrate of the same fungus was shown to inhibit the accumulation of isoflavone aglyca, isoflavone conjugates and phytoalexins in the sliced cotyledons. The possible relevance of elicitor‐suppressor counteraction with regard to the defence mechanisms of the host plant is discussed.

Antimicrobial Phytoprotectants and Fungal Pathogens: A Commentary

“…The induction of phytoalexins may be circumvented or delayed by evading recognition by the surveillance system of the host plant. There is also evidence for some plant-fungus interactions to indicate that fungi may produce molecules that suppress plant defence responses, including phytoalexin biosynthesis (Zeigler and Pontzen, 1982;Kessman and Barz, 1986;Shiriashi et al, 1992).…”

Suppression of Bean Defense Responses by Pseudomonas syringae.

“…Thus, compatible bacterial pathogens may have evolved mechanisms to inhibit or suppress the induction of plant defense responses. A number of studies have indicated that funga1 pathogens produce such suppressors of plant defense responses (Doke et al, 1980;Ziegler and Pontzen, 1982;Kessmann and Barz, 1986;Yamada et al, 1989). Transposon insertion mutants of Xanthomonas campestris pathovars have been isolated that induce hypersensitive reactions on normally susceptible plants, suggesting that bac-teria1 plant pathogens might also produce suppressors (Daniels et al, 1984;Kamoun et al, 1992); however, to date, no suppressor has been isolated from a bacterial pathogen.…”

Expression of the 12-Oxophytodienoic Acid 10,11-Reductase Gene in the Compatible Interaction between Pea and Fungal Pathogen

“…Therefore, pathogens must overcome the host resistance induced by various elicitors to succeed in the infection , Shiraishi et al 1994. The molecules able to suppress the active resistance of host plants to such responses as hypersensitive cell death (Doke 1975, Storti et al 1988, superoxide generation (Doke 1983), and accumulation of phytoalexin (Shiraishi et al 1978, Doke et al 1979, Kessmann and Barz 1986 are called suppressors (reviewed by Shiraishi et al 1994, Shiraishi et al 1999.…”