Partial Purification and Characterization of Exo-and-Endo-1,3- β-DGlucanases from Atriplex Leaf Tissues, their Involvement in Cell Extension Growth and the Effects of Salinity

Abstract

Summary β -D-glucanase activity from Atriplex leaf tissues is represented by an endo-1,3- ]sB -D-glucanase(EC 3.2.1.39) and an exo-1,3- β -D-glucanase (EC 3.2.1.58). The latter form is always associated with a β -glucosidase activity, suggesting that it is a bifunctional enzyme. The exo-enzyme, extractable only with a high-salt concentration buffer is confined to walls whereas the endo form which is weakly bound, could have multiple sites, i.e. walls and membranes of endoplasmatic reticulum. During leaf development of plants grown without sodium chloride, exo-glucanase activity is closely correlated to the lamina thickening rate. In leaves from plants grown in solutions containing 340 mM NaCl the lamina thickening is increased while exo-1,3- β -glucanase activity is the same as that in plants cultivated without salt. Under both culture conditions endo-1,3- β -glucanase activity seems to remain more or less constant during lamina thickening. Gel filtration shows at least two forms of endo-glucanases: EG-1 and EG-2. Following ion exchange chromatography EG 1 is detected in the void volume while some of the EG-2 is eluted with 0.28 M NaCl (EG-2B) and the majority with 0.5 M NaCl (EG-2A). These various endoforms have the same affinity for laminarin but have different molecular weights, heat stabilities, and sodium chloride sensitivities in vitro . Culture at the highest salinity level induces a change in EG-1: EG-2 ratio due to a significant increase of EG-1 activity. The role of exo-1,3- β -glucanase in cell extension growth via cell wall remodeling is considered. The adaptative significance of endo-1,3- β -glucanase activity in salt-rich culture is discussed.