Ultrastructural changes in the pericarp of tomato (Lycpekon escudentun Mill) fruit were followed during ripening. Ethylene production was monitored by gas chromatography and samples analyzed at successive stages of the ripening process.Changes in the cytoplasm}c uktrastructure were not consistent with the suggestion that ripening is a 'senescence' pbenomenon. A large degree of ultrastructural organization, especially of the mitochondria, chromoplasts, and rough endoplasmic reticulum, was retained by ripe fruit.Striking changes in the structure of the cell wall were noted, begnning with dissolution of the middle lamella and eventual disruption of the primary cell wall. These changes were correlated with appearance of polygalacturonase (EC 3.2.1.15) isoenzymes. Application of purifli tomato polygalacturonase lsoenzymes to mature green fruit tissue duplicated the changes in the cell wall noted duing normal ripening. Possible roles of the polygalacturonase isoenzymes in cell wall disorganizadon are discussed.

No abstract