Galactose metabolism and ethylene production during development and ripening of tomato fruit

Abstract

During tomato fruit growth, a steady decline in cell wall galactosyl residues was accompanied by an increase in soluble galactose and occurred in both ‘Rutgers’ and non-ripening mutant rin fruit. However, after maturation and a cessation in the net decrease in galactosyl residues between the mature green and breaker stages of ripeness, ‘Rutgers’ fruit exhibited an abrupt, ripening-related decrease in cell wall galactosyl residues and increase in soluble galactose; rin fruit did not. The net decrease in pericarp cell wall galactosyl residue content occurred significantly before an increase in internal ethylene concentration, however, the increase in soluble galactose did not. Mutant rin fruit showed a constant rate of galactosyl residue loss throughout ontogeny and no increase in soluble galactose occurred. Galactokinase, UDP-galactose pyrophosphorylase, and UDP-galactose-4′-epimerase activities were detected in tomato fruit throughout development and senescence. However, no significant difference in the activities of the three enzymes was found between ‘Rutgers’ and rin fruit. Results show that the decrease in galactosyl content occurs separate from the increase in ethylene evolution and that the resulting increase in monomeric galactose is most likely due to an increase in the rate of galactosyl solubilization from the cell wall, rather than from a decrease in ability to metabolize solubilized galactose.