| Research Abstract |
Signal transduction in response of plant cells to fungal infection and its elicitor and regulatory aspects of the signal transduction by host-selective pathogenicity-determinants in relation to pathogen-reception were determined and discussed. Potato tuber tissues hypersensitively reacted to infection with an incompatible race of Phytophthora infestans and its hyphal wall components (HWC) with a transient enhancement of a superoxide-generating system (SOX), phospholipase A_2, lipoxygenase and lipid-peroxidation in association with following production of phytoalexin. G-protein, Ca^<++>, calmodulin (CaM), Ca^<++>/Cam dependent protein kinase were shown to be involved in the activation of SOX by using inhibitors. The in vitro activation of SOX in plasmamembrane fraction of potato tissues was stimulated by HWC-treatment in the presence of Ca^<++>, ATP and soluble protein fraction. Suspension cultured cells of several Slanaceous plants responsed to HWC, showing an immediate movement of Ca^
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<++> from membrane and activation of superoxide generation l min later. Ca^<++> chelator and channel-blocker suppressed the occurrence of these HWC-stimulated phenomena in the cells. A water soluble glucan (WSG) isoalted from Phytophthora mycelia or germination fluid also suppressed the occurrence of HWC-stimulated Ca^<++> relaese and SOX-activation in susceptible, but not resistant, host cells. The role of WSG was enphasized as a host-selective factor to suppress the signal transduction for the active response of plant cells to elicitor or infection. Modes of action of host-selective toxins, AF-and AL-toxins from Alternaria alternata strawberry and tomato pathotypes, respectively, were investigated. Af-toxin acted on a putative receptor on plasamamembrane of the susceptible clones, inducing pathogen-reception. AL-toxin was proposed to acte against phosphoethanolamine transferase of the susceptible tomato cultivas, causing a membrane dissociation by a inhibition of phosphatidylethanolamine synthesis. A host selective toxin isolated Bipolaris zeicola race 3, BZR toxin was characterized by 4 co-toxins which were synergistically active as susceptibility-inducer in the fungal hosts. Less
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