INDUCTION OF CHITINASE AND BETA-1,3-GLUCANASE ACTIVITY IN SUNFLOWER SUSPENSION CELLS IN RESPONSE TO AN ELICITOR FROM PHYTOPHTHORA-MEGASPERMA F SP. GLYCINEA (PMG) - EVIDENCE FOR REGULATION BY ETHYLENE AND 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID (ACC)

In heterotrophic cell suspensions of sunflower (Helianthus annuus L. c v. Spanners Allzweck) the effect of Pmg elicitor, a fungal elicitor pr eparation from Phytophthora megasperma f. sp. glycinea, on the inducti on of chitinase and beta-1,3-glucanase activity was studied in relatio n to changes in ethylene biosynthesis. Dose-response experiments with Pmg elicitor showed that the onset of the induction of intracellular c hitinase and beta-1,3-glucanase activity coincided or followed a trans ient rise in ethylene and particularly endogenous 1-aminocyclopropane- 1-carboxylic acid (ACC) levels within 5 h of application. Treatment wi th 5 mu g ml(-1) elicitor stimulated ethylene and ACC levels 1.6-fold and 4-fold, relative to control, respectively. The molar ratio of ACC to ethylene changed from approximately 3:1 in controls to 9:1 in treat ed cells. During further incubation, ethylene formation and, to a less er degree, ACC levels declined and the ACC/ethylene ratio increased to 56: 1 in elicitor-treated cells. On a protein basis, the activities o f beta-1,3-glucanase and chitinase increased approximately 5-fold and 8-fold, respectively, 48 h after elicitor application. Additional trea tment with the ACC synthesis inhibitor aminoethoxyvinylglycine (AVG) d ecreased elicitor-induced enzyme activities and the levels of both eth ylene and ACC. Elicitor effects on chitinase and beta-1,3-glucanase ac tivities could be fully restored when ACC was additionally applied. Co ncomitantly, the ACC/ethylene ratio increased. Neither treatments with ACC alone, which simultaneously increased internal ACC and ethylene l evels, nor treatments with AVG alone, which simultaneously reduced ACC and ethylene levels, could generally stimulate chitinase or beta-1,3- glucanase activities in the cells. It is suggested that ACC functions as a promoting factor in the induction of chitinase and beta-1,3-gluca nase activity triggered by Pmg elicitor and appears to reverse an inhi biting influence of ethylene.