ASSOCIATION BETWEEN ION FLUXES AND DEFENSE RESPONSES IN PEA AND COWPEA TISSUES

The glycopeptide elicitor from a pea pathogen, Mycosphaerella pinodes, induced rapid alkalinization and increases in levels of Na+ and K+ io ns in the extracellular solution upon contact with pea and cowpea tiss ues, The presence of monensin, nigericin, lidocaine, quinidine or phen ytoin together with the elicitor markedly inhibited these changes, whe reas the presence of valinomycin, gramicidin D, tetraethylammonium, Cs Cl and aminopyridine did not. The production of phytoalexins in pea an d cowpea tissues was also strongly inhibited by the simultaneous prese nce of the former reagents but not of the latter reagents. Inhibitory effects on the production of phytoalexins were diminished when monensi n, nigericin or a Na+-channel blocker was applied 3 h after the start of treatment with elicitor, Furthermore, orthovanadate and neomycin, w hich suppress defense responses in both tissues, also inhibited the ab ove mentioned changes. By contrast, the species-specific suppressor fr om M. pinodes inhibited the elicitor-induced release of Na+ and K+ ion s from pea tissues, but, conversely, by itself it elicited either the defense response or the release of Na+ and K+ ions from cowpea tissues . The results indicate that these ion-related changes, in particular t he efflux of Na+ and K+ ions, might be closely associated with the sig nal transduction system for defense responses at the tissue level.