| Research Abstract |
REGULATION OF ATPASE AND SIGNAL TRANSDUCTION FOR PEA DEFENSE RESPONSES BY THE SUPPRESSOR AND ELICITOR FORM MYCOSPHAERELLA PINODES
A pea pathogen, Mycosphaerella pinodes, secretes a polysaccharide elicitor (MW = ca.70,000) and glycopeptide suppressors for defense responses of pea plants in its pycnospore germination fluid. Recently, the structures of two suppressors, Supprescin A and B, were determined as GalNAc-Ser-Ser-Gly and Gal-GalNAc-Ser-Ser-Gly-Asp-Glu-Thr, respectively (Plant Cell Physiol.33 : 663-667, 1992). Though these suppressors inhibited the production of pisatin, a major phytoalexin of pea plants, only Supprescin B inhibited the ATPase activity in vitro. The mode of action of two suppressors and the eleven synthesized peptides on the ATPase activity in isolated pea plasma membranes was analyzed. Supprescin B and eight kinds of peptides inhibited the activity. They were classified into three groups in a manner of ATPase-inhibition such as competitive, non-competitive and a m
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ixed type of both. In the next, the effect of fungal signals on the transmembrane signaling for pea defense responses was investigated with the elicitor and a partially purified suppressor including Supprescin A and B.In vivo and in vitro, the elicitor rapidly activated several enzymes associated with polyphosphoinositide (PI) metabolism, especially, phosphatidylinosotol- and phosphatidylinositol-monophosphate kinases, and phospholipase C with 5 and 30 sec, respectively. However, the concomitant presence of suppressor inhibited these activations. Several inhibitors for pisatin production, such as K252a, neomycin or orthovanadate, also brock the activation of PI-metabolism induced by the elicitor. These results suggest that the activation of PI-metabolism is an indispensable process during the elicitation of defense response of pea plants. A metabolite in PI-metabolism, PIP2, enhanced the ATPase activity and an inhibitor of PLC, neomycin, reduced it. On the other hand, an inhibitor of P-type ATPase, orthovanadate, suppressed the PI-metabolism. These findings strongly suggest that a "cross-talk" between the ATPas Less
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