β-Galactosidase and α-L-Arabinofuranosidase Activities and Gene Expression in European and Chinese Pear Fruit During Ripening

Abstract

Substantial decreases in cell wall bound galactosyl and arabinosyl residues are two of the most evident cell wall compositional changes that occur during fruit ripening. The roles of β-galactosidase (β-Gal) and α-L-arabinofuranosidase (α-Af), the enzymes responsible for these respective losses, were investigated and compared in European (Pyrus communis L. ‘La France’) and Chinese (Pyrus bretschneideri Rehd. ‘Yali’) pear fruits which exhibit different softening characteristics during ripening. The increase in the activities of β-Gal and α-Af during ripening in both types of pear fruit correlated well with an increase in climacteric ethylene production, and a concomitant decrease in flesh firmness in ‘La France’ fruit. However, there was no noticeable decrease in ‘Yali’ flesh firmness even after 28 days of storage at room temperature. In both fruit types, enzyme activity and the accumulation of transcripts hybridizing with PpGAL1, PpGAL4, PpARF2, and PcARF1 increased with fruit ripening. Increases in gene expression and enzyme activities in ‘Yali’ fruit with no detectable softening during ripening indicate that β-Gal and α-Af may not mediate difference in fruit softening between two pears, but that they could play some role(s) in cell wall changes, perhaps in cooperation with other cell wall-modifying enzymes such as polygalacturonase.