Are ethylene and 1-aminocyclopropane-1-carboxylic acid involved in the induction of chitinase and ?-1,3-glucanase activity in sunflower cell-suspension cultures?

Abstract

Auxin-dependent, heterotrophic suspension cells of sunflower (Helianthus 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 treatment with 10−5 mol·L−1 of the triazole-type growth retardant BAS 111.W. In proportion to this increase, chitinase activity appeared to be excreted into the culture medium. The intracellular activity of β-1,3-glucanase, assayed fluorimetrically with laminarin as the substrate, was only slightly enhanced. Dose-response experiments with BAS 111.W showed that the onset of the induction of chitinase activity coincided with an inhibition of ethylene formation and an accumulation of endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) as a result of blocking the conversion of ACC to ethylene. Other nitrogen-heterocyclic growth retardants (e.g. tetcyclacis, ancymidol), the triazole-type fungicide BAS 480.F, salicylic acid, CoCl2 and 2,4-dichlorophenoxy-acetic acid, which also increased the ACC/ethylene ratio, similarly induced chitinase activity. In contrast, aminoethoxy vinylglycine, which simultaneously lowered endogenous ACC and ethylene formation, did not stimulate chitinase activity. However, after addition of BAS 111.W and ACC, an accumulation of endogenous ACC was accompanied by a strong induction of the enzymatic activity. This effect did not correlate with changes in the cell culture growth nor in the cellular contents of immunoreactive abscisic acid, 3-indoleacetic acid, gibberellins or cytokinins. Furthermore, ethephon, which chemically generates ethylene, led to a slight reduction in ACC levels and tended to decrease chitinase activity relative to the control. In conclusion, it is hypothesized that the induction of chitinase activity in sunflower cell suspensions is antagonistically regulated by ethylene and ACC. At least at higher production rates, ethylene appears to function as an inhibiting factor whereas ACC may be a promoting one. The stimulation of chitinase and β-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 compounds which possibly leads to an increased resistance of plants to fungal infections.