Induction of chitinase and β-1,3-glucanase activity in sunflower suspension cells in response to an elicitor fromPhytophthora megaspermaf. sp.glycinea(Pmg). Evidence for regulation by ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC)

Abstract

In heterotrophic cell suspensions of sunflower (Helianthus annuus L. cv. Spanners Allzweck) the effect of Pmg elicitor, a fungal elicitor preparation from Phytophthora megasperma f. sp. glycinea, on the induction of chitinase and /?-1 ,3-glucanase activity was studied in relation to changes in ethylene biosynthesis. Dose-response experiments with Pmg elicitor showed that the onset of the induction of intracellular chitinase and /M ,3-glucanase activity coincided or followed a transient rise in ethylene and particularly endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) levels within 5 h of application. Treatment with 5 /*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 treated cells. During further incubation, ethylene formation and, to a lesser degree, ACC levels declined and the ACC/ethylene ratio increased to 56:1 in elicitor-treated cells. On a protein basis, the activities of /M ,3-glucanase and chitinase increased approximately 5-fold and 8-fold, respectively, 48 h after elicitor application. Additional treatment with the ACC synthesis inhibitor aminoethoxyvinylglycine (AVG) decreased elicitorinduced enzyme activities and the levels of both ethylene and ACC. Elicitor effects on chitinase and /M ,3-glucanase activities could be fully restored when ACC was additionally applied. Concomitantly, the ACC/ ethylene ratio increased. Neither treatments with ACC alone, which simultaneously increased internal ACC and ethylene levels, nor treatments with AVG alone, which simultaneously reduced ACC and ethylene levels, could generally stimulate chitinase or /M ,3-glucanase activities in the cells. It is suggested that ACC functions as a promoting factor in the induction of chitinase and /M ,3-glucanase activity triggered by Pmg elicitor and appears to reverse an inhibiting influence of ethylene.