ROS metabolism and ripening of fleshy fruits

The ripening of fleshy fruit is a complex physiological process that involves drastic changes at phenotypic, genomic, proteomic, and biochemical levels, where the different subcellular compartments undergo biochemical and metabolic reorganizations, the shift of chloroplasts to chromoplasts being perhaps the best example. In this process, the unripe fruits become an edible ripe product in which the metabolism of reactive oxygen species (ROS) has a relevant leading role. ROS are involved in the regulation of the ripening of climacteric and non-climacteric fruits due to their functions as signaling molecules in coordination with other compounds, including phytohormones (ethylene), nitric oxide (NO), hydrogen sulfide (H2S), and melatonin. ROS metabolism is also very relevant during postharvest storage of fruits, where it can exert a dual effect since it can trigger oxidative damage contributing to the loss of fruit quality but, on the other hand, it can exert a protective role against pathogens. From an anthropic point of view, there are different categories of fleshy and edible fruits, with many representatives possessing high content of antioxidant properties. Their nutraceutical properties can improve human health, especially considering fruits are predominantly eaten fresh, consequently maintaining their antioxidant properties at consumption, which could be lost otherwise by cooking.