Original language | English |
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Title of host publication | Encyclopaedia of Applied Plant Sciences |
Publisher | Academic Press |
Publication status | Published - 6 Sept 2016 |
Abstract
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.
Keywords / Materials (for Non-textual outputs)
- cell wall
- collenchyma
- Cytoplasm
- epidermis
- nucleus
- organalles
- parenchyma
- protoplast
- sclerenchyma
- xylem