Characterization and function of wall-bound exo-β-glucanases of Lilium longiflorum pollen tubes

Two exo-beta-glucanases (LP-ExoI, 83 kDa and LP-ExoII, 71 kDa) were extracted and partially purified from the cell wall of Lilium longiflorum pollen tubes. Both LP-ExoI and LP-ExoII hydrolyzed laminarin (1,3-beta-glucan). These enzymes also exhibited some activity toward 1,3:1,4-beta-glucans of Hordeum vulgare and Cetraria islandica and the 1,6-beta-glucan of Umbilicaria papullosa. The pH for optimum activity for both exo-beta-glucanases was 5.5. Methylation analysis of the reaction products revealed that purified LP-ExoI decreased both 1,3- and 1,4-glucosyl linkages in hemicellulosic polysaccharides isolated from the cell wall of lily pollen tubes. D-gluconolactone and nojirimycin, inhibitors of glucosidase, inhibited activities of both exo-beta-glucanases, as well as growth of the lily pollen tubes. These results disclosed that the wall-bound exo-beta-glucanases play an important role in the regulation of lily pollen tube growth.