ARE ETHYLENE AND 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID INVOLVED IN THE INDUCTION OF CHITINASE AND BETA-1,3-GLUCANASE ACTIVITY IN SUNFLOWER CELL-SUSPENSION CULTURES

Auxin-dependent, heterotrophic suspension cells of sunflower (Helianth us annuus L. C.K. Spanners All-zweck) showed, on a cell-protein basis, a seven-fold increase in chitinase activity, which began 5 d after tr eatment with 10(-5) mol . L-1 of the triazole-type growth retardant BA S 111..W In proportion to this increase, chitinase activity appeared t o be excreted into the culture medium. The intracellular activity of b eta-1,3-glucanase, assayed fluorimetrically with laminarin as the subs trate, was only slightly enhanced. Dose-response experiments with BAS 111..W showed that the onset of the induction of chitinase activity co incided with an inhibition of ethylene formation and an accumulation o f endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) as a result o f blocking the conversion of ACC to ethylene. Other nitrogen-heterocyc lic growth retardants (e.g. tetcyclacis, ancymidol), the triazole-type fungicide BAS 480..F, salicylic acid, CoCl2 and 2,4-dichlorophenoxyac etic acid, which also increased the ACC/ethylene ratio, similarly indu ced chitinase activity. In contrast, aminoethoxy vinylglycine, which s imultaneously lowered endogenous ACC and ethylene formation, did not s timulate chitinase activity. However, after addition of BAS 111..W and ACC, an accumulation of endogenous ACC was accompanied by a strong in duction of the enzymatic activity. This effect did not correlate with changes in the cell culture growth nor in the cellular contents of imm unoreactive abscisic acid, 3-indoleacetic acid, gibberellins or cytoki nins. Furthermore, ethephon, which chemically generates ethylene, led to a slight reduction in ACC levels and tended to decrease chitinase a ctivity relative to the control. In conclusion, it is hypothesized tha t the induction of chitinase activity in sunflower cell suspensions is antagonistically regulated by ethylene and ACC. At least at higher pr oduction rates, ethylene appears to function as an inhibiting factor w hereas ACC may be a promoting one. The stimulation of chitinase and be ta-1,3-glucanase activity, caused by the retardant BAS 111..W and the fungicide BAS 480..F, is discussed as an additional effect of both com pounds which possibly leads to an increased resistance of plants to fu ngal infections.