ELICITOR AND SUPPRESSOR EFFECTS ON PHOSPHOLIPASE-C IN ISOLATED PLASMA-MEMBRANES CORRELATE WITH ALTERATIONS IN PHENYLALANINE AMMONIA-LYASE ACTIVITY OF WHEAT LEAVES

Injection of Pgt(DEAE)-elicitor prepared from germ tubes of Puccinia g raminis f.sp. tritici into the intercellular space of wheat leaves ind uced an 8-fold increase in phenylalanine ammonia-lyase (PAL; EC 4.3.1. 5) activity within 24 h. The elicitor activity could be significantly suppressed to about 40 % of its level in the elicitor-treated controls by simultaneous application of an intercellular washing fluid fractio n (IWFG2) of susceptible stem rust infected wheat leaves. Additional e xperiments revealed an obvious correlation between the effects of the elicitor/suppressor-preparations on the wheat leaf PAL activity and on the plasma membrane associated phospholipase C activity (PLC; EC 3.1. 4.3) hydrolyzing phosphatidylinositol 4,5-bisphosphate (PIP2). Apparen tly, the Pgt(DEAE)-elicitor Stimulated the PLC activity slightly betwe en 9 and 36 % over the control level, while the IWFG2-fraction inhibit ed PIP2 cleavage substantially to about 50 % of the controls. Our resu lts point to an involvement of the phosphoinositide metabolism in the Pgt-elicitor mediated wheat/stem rust-interaction. In contrast, when u sing a chitin-derived elicitor preparation (COS), different results we re obtained, indicating that COS may act through a different mechanism .