Non-specific glycopeptide elicitors of Cladosporium fulvum: evidence for involvement of active oxygen species in elicitor-induced effects on tomato cell suspensions

Abstract

The responses of cell suspension cultures, produced from tomato lines near isogenic for resistance genes Cf4 and Cf5, to glycopeptide non-specific elicitors (NSE) of Cladosporium fulvum race 4 were investigated to determine if active oxygen (AO) species were involved in the initial host reaction, as reported for the fungal produced specific elicitors present in intracellular washing fluids from C. fulvum infected leaves. Cells treated with NSE showed increases in: (1) malonaldehyde (a product of lipid peroxidation), (2) cytochrome c reducing activity which was inhibited by superoxide dismutase (SOD) (an assay for superoxide), (3) activity of extracellular peroxidases, (4) extracellular phenolic compounds, and (5) oxygen uptake. The addition of catalase, SOD, ascorbate (a scavenger of superoxide), mannitol (a scavenger of the hydroxyl radical), KGN and salicyl hydroxamic acid (SHAM) (both inhibitors of peroxidases) prior to NSE-treatment reduced the elicitor-induced increases in malonaldehyde and extracellular phenolics. Catalase was an effective inhibitor of the induced increases in oxygen uptake and cytochrome c reducing activity. The TLC profiles of phenolic compounds induced by both NSE and specific elicitors were similar. NSE-induced effects differed from those caused by specific elicitors by the failure to detect luminol-dependent chemiluminescence (LDC) (an assay for several AO species) and the increase, rather than decrease, in oxygen uptake.