Ripening is not just the random deterioration of biological processes in the fruit. Specific biochemical processes are activated during fruit ripening that account for the changes that are collectively known as ripening. It is now known that the plant hormone ethylene plays a central role in tomato fruit ripening. When synthesis of ethylene is blocked, using chemical inhibitors of the enzymes of ethylene synthesis, tomato fruits will not ripen. The enzyme that catalyzes the first step is ACC synthase, and the second step is catalyzed by ACC oxidase.
Ethylene then acts as a hormone to regulate the ripening process.
Ethylene is also involved in other facets of plant growth, including seedl germination and seedling growth, leaf abscission, petal senescence, responses to environmental stress. In fruit ripening, ethylene activates the expression of many genes. These gene products, usually proteins, are then responsible for the specific changes that occur during ripening. It is clear that there are a number of steps at which the biotechnologist could intervene to modify fruit ripening, as indicated below. The first method to reduce the synthesis of ethylene that I will describe has been developed by a relatively small biotech company in Oregon called Agritope.