|Title of host publication||Encyclopaedia of Applied Plant Sciences|
|Publication status||Published - 6 Sep 2016|
Ripening in ‘climacteric’ fruits (most commercial species) is induced by a burst of endogenous ethylene. What triggers this burst remains uncertain. The ‘climacteric’ is a sudden increase in ethylene and CO2 output. Ripening makes fruits attractive to animals. Chlorophylls are degraded and non-green pigments (carotenoids and/or anthocyanins) are synthesised, increasing the fruit’s visibility against a leafy background. Starch, organic acids and tannins decrease; sugars and aromas increase — all increasing palatability. Cellular membranes become permeabilised, allowing protoplasmic solutes into the apoplast; the fruit becomes a more oxidising environment, containing H2O2 and hydroxyl radicals. Wall-polysaccharide-modifying enzymes increase, especially endo-polygalacturonases, cellulases, xyloglucan endotransglucosylase/endohydrolases, -galactosidases, pectin-methylesterases and pectate lyases. These enzymes, and -expansins, loosen the wall and/or middle lamella, softening the fruit. Also, apoplastic hydroxyl radicals and calcium-chelators may solubilise wall polysaccharides, promoting softening. Ripening is a robust phenomenon: knocking out any individual player (e.g. endo-polygalacturonase) usually does not prevent normal softening.
- cell wall