beta-Galactosidase and alpha-L-Arabinofuranosidase in Cell Wall Modification Related with Fruit Development and Softening

Fruit softening and textural changes are two important factors of fruit quality. The loss of galactosyl and arabinosyl residues from cell wall polysaccharides is observed in many fruit species during ripening. The release of neutral sugar residues could change wall polysaccharides properties of accessibility or reactivity for other cell wall hydrolases. beta-Galactosidase and alpha-L-arabinofuranosidase contribute to the loss of neutral sugar residues. Thus, the enzymes alter polysaccharide properties and might contribute to fruit softening or textural changes during ripening. beta-Galactosidase is composed of multiple isozymes and they are clearly distinguishable by their substrate specificity and expression pattern of the related gene. A transgenic experiment revealed that a beta-galactosidase isozyme plays an important role in tomato fruit softening. In addition to fruit softening, the contribution of beta-galactosidase to plant development is also indicated. alpha-L-Arabinofuranosidase genes constitute a gene family and the isozymes are expressed in various organs and stages. Moreover, several alpha-L-arabinofuranosidases possess beta-xylosidase activity in addition to alpha-L-arabinofuranosidase activity, therefore, substrate specificity against native polysaccharides is very complex. Arabinose containing polysaccharides seem to contribute to cell to cell adhesion but the crucial roles of alpha-L-arabinofuranosidase in fruit development or softening remain unclear. Further biochemical and physiological studies of the enzyme are required.