Release of phytoalexins and related isoflavonoids from intact chickpea seedlings elicited with reduced glutathione at root level

Induction of phytoalexin formation in roots of chickpea (Cicer arietinum L. ) seedlings treated with the reduced form of glutathione (GSH) was investig ated. Accumulation of phytoalexins and constitutive isoflavonoids upon GSH treatment was assessed by high performance liquid chromatography analysis o f extracts from roots and liquid incubating media of seedlings, whereas the requirement for concurrent de novo synthesis of induced compounds was asse ssed in elicitation studies conducted in the presence of key enzyme inhibit ors of the phenylpropanoid pathway and/or [U-C-14]-L-phenylalanine. The res ults indicate that: (a) GSH elicits the formation not only of the pterocarp an phytoalexins medicarpin and maackiain, but also that of the constitutive isoflavones biochanin A and formononetin and, in seedlings older than 4 d, that of the isoflavanones homoferreirin and cicerin. (b) GSH-induced secon dary metabolites do not accumulate in plant root tissue; rather, they are r eleased into the surrounding external medium. (c) Phytoalexins and isoflavo noids induced by GSH are de novo synthesized from early phenylpropanoid pat hway precursors rather than derived from pre-existing conjugate forms or im mediate precursors. (d) Because of metabolic competence and/or proximity, o nly a small proportion of root cells is responsive to GSH elicitation, henc e the very small amounts or absence of induced compounds detected in root t issue samples. (C) 2001 Editions scientifiques et medicates Elsevier SAS.