Exo- and endoglucanases of maize coleoptile cell walls: their interaction and possible regulation

Glucanase-mediated degradation of beta-(1,3)(1,4)-glucans has been attribut ed to auxin-induced cell wall loosening and thus tissue growth in cereal pl ants, but the regulatory mechanisms for the auxin-enhancement of glucanase activities in situ are not fully understood. Here, we report evidence for p ossible mechanisms which might account for auxin-induced changes in glucana se activities. A likely cause for acceleration of wall glucan degradation i s the change in the ratio of exo- and endoglucanases. The combined enzymes synergistically promote beta-(1,3)(1,4)-glucan hydrolysis. In addition, the se enzyme activities are enhanced by other enzymic and non-enzymic proteins and are also partially stimulated by divalent cations such as Ca2+ and Mg2 + at certain pH values. The acceleration of glucan degradation mediated by auxin may be mediated by changes and/or interactions of any of these factor s in situ. (C) 2000 Elsevier Science B.V. All rights reserved.