CHARACTERIZATION OF METABOLIC CHANGES INVOLVED IN HYPERSENSITIVE-LIKE BROWNING REACTIONS OF CHICKPEA (CICER-ARIETINUM L) CELL-CULTURES FOLLOWING CHALLENGE BY ASCOCHYTA-RABIEI CULTURE FILTRATE

A putative protein in the culture filtrate of Ascochyta rabiei induced a rapid browning response in cell cultures derived from an A. rabiei resistant cultivar of chickpea (Cicer arietinum). Toluidine blue O staining showed massive deposition of phenolic material in the cell wall. Reduced fluorescence after fluorescein diacetate treatment revealed impaired cells, although the cells still showed plasmolysis and deplasmolysis indicating an intact plasma membrane and therefore viability. These reactions could not be detected in cell cultures derived from a susceptible chickpea cultivar. The cultivar-specific cell browning strictly correlated with rapid metabolism of several constitutive isoflavonoid malonylglucoside conjugates. The fate of the pterocarpan phytoalexin medicarpin was closely analysed. The level of medicarpin malonylglucoside decreased rapidly after culture filtrate application and simultaneously, medicarpin was found in alkaline hydrolysable form in cell wall components. Evidence that the active component in the culture filtrate is a protein was based on the observations that the browning inducing activity of the culture filtrate was destroyed by proteinase K and heat treatment. © 1994 Academic Press, Inc.