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 graminis f.sp. tritici into the intercellular space of wheat leaves induced 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 fraction (IWFG2) of susceptible stem rust infected wheat leaves. Additional experiments 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). Apparently, the Pgt(DEAE)-elicitor Stimulated the PLC activity slightly between 9 and 36 % over the control level, while the IWFG2-fraction inhibited PIP2 cleavage substantially to about 50 % of the controls. Our results point to an involvement of the phosphoinositide metabolism in the Pgt-elicitor mediated wheat/stem rust-interaction. In contrast, when using a chitin-derived elicitor preparation (COS), different results were obtained, indicating that COS may act through a different mechanism.