Glycosidases in Cell Wall-degrading Extracts of Ripening Tomato Fruits

Abstract

(14). The modification of cross-linking polymers could contribute to the loss of wall structure and fruit firmness that occurs during ripening. If this were so, softening could be at least partly attributable to the action of enzymes that cleave bonds between sugars other than galacturonic acid. In the work reported here, we studied the glycosidase activity of cell wall-degrading extracts of ripening tomato fruits. MATERIALS AND METHODSThe softening that occurs during the ripening of many fruits is presumably the result of enzymatic modifications of cell wall polysaccharides. The polysaccharide network of the wall contains bonds that are susceptible to a variety of hydrolytic enzymes. These enzymes include cellulase, polygalacturonase, and the enzymes that hydrolyze noncellulosic neutral polysaccharides.

Cell Wall Metabolism in Ripening Fruit (VI. Effect of the Antisense Polygalacturonase Gene on Cell Wall Changes Accompanying Ripening in Transgenic Tomatoes)

“…The slight decline in a-arabinosidase and a-galactosidase activities and marginal increase in P-galactosidase activity found (Fig. 1, B-D) are similar to those previously reported (Wallner and Walker, 1975;Campbell et al, 1990). Generally, glycosidase activities were similar in control and transgenic plants, supporting a specific effect of the antisense PG gene on PG.…”

Tomato Fruit Cell Wall

“…The PE fraction did not release any detectable carbohydrate derived from cell wall polymers when assayed with tomato fruit walls as substrate. Glycosidase activity was absent even after 1 h incubation of this fraction when assayed according to Wallner and Walker (30) D-mannoside were purchased from Koch-Light Laboratories, all others from Sigma Chemical Co.). The PE fraction contained some a-amylase.…”

“…Because mature green (MG) fruit tissue contains substantial PE activity, but no PG, it was feasible to exploit autolysis to deesterify native pectins (24,30). Frozen …”

The beta subunit of tomato fruit polygalacturonase isoenzyme 1: isolation, characterization, and identification of unique structural features.

“…The activity of the pectin-hydrolyzing cell wall enzyme polygalacturonase (PG; EC 3.2.1.15) increases dramatically during the ripening of many fruits and has been shown to be the primary enzymic activity responsible for cell wall polyuronide degradation in ripening tomato fruit (Wallner and Walker, 1975;Themmen et al, 1982;Huber, 1983;Brady et al, 1987;Smith et al, 1988;Giovannoni et al, 1989). In tomato, thecatalytic PG polypeptide is encoded by a single gene (the PG gene) whose expression and function have been extensively studied in recent years (reviewed in Giovannoni et al, 1990).…”