Subcellular Distributions of Isoenzymes in Fruits of a Normal Cultivar of Tomato and of the rin Mutant at Two Stages of Development

Fruits of tomato (Lycopersicon esculentum Mill.) cv. Rutgers and of a nearly isogenic stock containing the ripening inhibitor gene rin harvested at green (66% mature) and ripe (107% mature) stages were studied for the subcellular distribution of isoenzymes using isoelectric focusing. The enzymes studied were peroxidases, esterases, phosphatases, phosphorylase, malate dehydrogenases, and IAA oxidases. During ripening of normal fruit the activities in the supernatant fraction of all of these enzymes, except malate dehydrogenase, decreased. In the particulate fractions some enzymes decreased while others increased in activity. The rin gene inhibited only some of the changes which occurred during ripening of normal fruit. It is postulated that changes in the degree to which enzymes are bound to membranes comprise one of the mechanisms by which the activities of enzymes are controlled in tomato pericarp, and that these membranes remain intact during ripening.