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 annuusL. cv. Spanners Allzweck) the effect of Pmg elicitor, a fungalelicitor preparation from Phytophthora megasperma f. sp. glycinea,on the induction of chitinase and ß-1,3-glucanaseactivity was studied in relation to changes in ethylene biosynthesis.Dose-response experiments with Pmg elicitor showed that theonset of the induction of intracellular chitinase and ß-1,3-glucanaseactivity coincided or followed a transient rise in ethyleneand particularly endogenous 1-aminocyclopropane-1-carboxylicacid (ACC) levels within 5 h of application. Treatment with5 µg ml^–1 elicitor stimulated ethylene and ACC levels1.6-fold and 4-fold, relative to control, respectively. Themolar ratio of ACC to ethylene changed from approximately 3:1in controls to 9:1 in treated cells. During further incubation,ethylene formation and, to a lesser degree, ACC levels declinedand the ACC/ethylene ratio increased to 56:1 in elicitor-treatedcells. On a protein basis, the activities of ß-1,3-glucanaseand chitinase increased approximately 5-fold and 8-fold, respectively,48 h after elicitor application. Additional treatment with theACC synthesis inhibitor aminoethoxyvinyiglycine (AVG) decreasedelicitor-induced enzyme activities and the levels of both ethyleneand ACC. Elicitor effects on chitinase and ß-1,3-glucanaseactivities could be fully restored when ACC was additionallyapplied. Concomitantly, the ACC/ ethylene ratio increased. Neithertreatments with ACC alone, which simultaneously increased internalACC and ethylene levels, nor treatments with AVG alone, whichsimultaneously reduced ACC and ethylene levels, could generallystimulate chitinase or ß-1,3-glucanase activitiesin the cells. It is suggested that ACC functions as a promotingfactor in the induction of chitinase and ß-1,3-glucanaseactivity triggered by Pmg elicitor and appears to reverse aninhibiting influence of ethylene. Key words: 1-Aminocyclopropane-1-carboxylic acid, chitinase, ß-1,3-glucanase, ethylene, Helianthus cellsuspension cultures, Phytophthora megasperma-elicitor