Characteristics of tomato cell wall degradation in vitro: implications for the study of fruit-softening enzymes

The in vitro degradation of green tomato (Lycopersicon esculentum L.) cell walls by an extract of ripe fruits was characterized. The susceptibility of isolated walls to enzymolysis varied considerably among the different cultivars tested. Wall solubilization in vitro appeared to be nearly as extensive as that which accompanies fruit ripening. The solubilized material was primarily polyuronide; smaller amounts of neutral sugar were released. Gel filtration chromatography indicated that an endopolygalacturonase was the only enzyme in the citrate extract able to hydrolyze isolated cell walls. However, this polygalacturonase in vitro did not lead to the substantial (40-60%) decrease in wall galactose which was observed in situ. This difference between in vitro and in situ wall modification is discussed in terms of the possible involvement of other wall hydrolases in fruit softening.