Ripening of pepper fruit and reactive nitrogen species

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Pepper (Capsicum annuum, Solanaceae) fruits are consumed worldwide and are of great economic importance. In most species ripening is characterized by important visual and metabolic changes, the latter including emission of volatile organic compounds associated with respiration, destruction of chlorophylls, synthesis of new pigments (red/yellow carotenoids plus xanthophylls and anthocyanins), formation of pectins and protein synthesis. The involvement of nitric oxide (NO) in fruit ripening has been established, but more work is needed to detail the metabolic networks involving NO and other reactive nitrogen species (RNS) in the process. It has been reported that RNS can mediate post-translational modifications of proteins, which can modulate physiological processes through mechanisms of cellular signalling.

Effect of exogenous NO gas on the ripening of pepper fruits. NO (5 p.p.m.) was either applied or not applied to fruits at an early breaking point stage for 1 h. Then, peppers were incubated at room temperature for 3 d.
Effect of exogenous NO gas on the ripening of pepper fruits. NO (5 p.p.m.) was either applied or not applied to fruits at an early breaking point stage for 1 h. Then, peppers were incubated at room temperature for 3 d. Image from Chaki et al.

Chaki et al. examine the role of reactive nitrogen species (RNS) and find that an enhancement of nitrosothiols and nitroproteins during ripening is reversed by exposure to nitric oxide (NO), which delays the ripening process. A decrease in catalase in red fruit implies a lower capacity to scavenge hydrogen peroxide, thus promoting lipid peroxidation in ripe fruit, and the results suggest that this decrease is due not only to a lower content of catalase but also to its nitration. Thus RNS can mediate post-translational modifications of proteins, which can modulate physiological processes through mechanisms of cellular signalling.

This article appears in the special issue ROS and NO Reactions in Plants.


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