Studies on the acidic wall proteins that activate the wall glucanases in maize coleoptiles.

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Exo- and endoglucanases purified from the cell walls of maize coleoptiles mediate a specific degradation of cell wall β-(1,3)(1,4)-glucans. We now suggest that there is a possible role for apoplastic chitinase in the cell wall glucan-glucanase interaction resulting in an acceleration of these reactions. The acidic wall protein fraction which had been isolated from maize coleoptiles is capable of endochitinase activity. Moreover, this purified maize acidic chitinase strongly stimulates both exo- and endoglucanases in catalyzing the hydrolysis of β-(1,3)(1,4)-glucans. Selected chitinases from other sources exhibited similar behavior in β-glucan hydrolysis in the presence of glucanases. However, we found no evidence to suggest that chitinases alone were responsible of significant hydrolysis of β-glucans in the absence of glucanases. These results suggest that the wall chitinase(s) may cause small but significant changes in either the glucanase glycopeptide structure or that it might act to modify certain conformational elements of the glucan structure.In cereal plants, auxin stimulates cell elongation, a process that is closely tied to metabolic modification of cell wall glucans. The precise nature of the chitinase interaction with the cell wall structural changes mediated by glucanases and the relationship to auxin action will be the focus of future experiments.