Ethylene and fruit softening

This review is concerned with the mechanisms controlling fruit softening. Master genetic regulators switch on the ripening programme and the regulatory pathway branches downstream, with separate controls for distinct quality attributes such as colour, flavour, texture, and aroma. Ethylene plays a critical role as a ripening hormone and is implicated in controlling different facets of ripening, including texture change, acting through a range of transcriptional regulators, and this signalling can be blocked using 1-methylcyclopropene. A battery of at least seven cell-wall-modifying enzymes, most of which are synthesized de novo during ripening, cause major alterations in the structure and composition of the cell wall components and contribute to the softening process. Significant differences between fruits may be related to the precise structure and composition of their cell walls and the enzymes recruited to the ripening programme during evolution. Attempts to slow texture change and reduce fruit spoilage by delaying the entire ripening process can often affect negatively other aspects of quality, and low temperatures, in particular, can have deleterious effects on texture change. Gene silencing has been used to probe the function of individual genes involved in different aspects of ripening, including colour, flavour, ethylene synthesis, and particularly texture change. The picture that emerges is that softening is a multi-genic trait, with some genes making a more important contribution than others. In future, it may be possible to control texture genetically to produce fruits more suitable for our needs.