Abstract
Plant central metabolism generates reactive oxygen species (ROS), which are key regulators that mediate signalling pathways involved in developmental processes and plant responses to environmental fluctuations. These highly reactive metabolites can lead to cellular damage when the reduction-oxidation (redox) homeostasis becomes unbalanced. Whilst decades of research have studied redox homeostasis in leaves, fundamental knowledge in fruit biology is still fragmentary. This is even more surprising when considering the natural profusion of fruit antioxidants that can process ROS and benefit human health. In this review, we explore redox biology in fruit and provide an overview of fruit antioxidants with recent examples. We further examine the central role of the redox hub in signalling during development and stress, with particular emphasis on ascorbate, also referred to as vitamin C. Progress in understanding the molecular mechanisms involved in the redox regulations that are linked to central metabolism and stress pathways will help to define novel strategies for optimising fruit nutritional quality, fruit production and storage.
Highlights
Reduction-oxidation processes are a major consequence of the presence of ground-state oxygen gas (O2, constituting c.a. 20.8% of the atmosphere) as a natural oxidant on Earth
This study revealed that higher ASC in ripening orange was associated with an augmented expression of four genes involved in ASC biosynthesis, encoding GDPd-mannose-3′,5′-epimerase (EC 5.1.3.18), GDP-l-galactosephosphorylase (EC 2.7.7.69), l-galactose dehydrogenase (EC 1.1.1.316) and l-galactono-1,4-lactone dehydrogenase (EC 1.3.2.3), together with attenuated activities of ASC oxidase and ASC peroxidase, which are involved in ASC degradation
Antioxidant mechanisms (e.g. ASC total pool and redox state, ASC-GSH cycle) are important actors throughout fruit growth, which is further evidence for the idea that reactive oxygen species (ROS) act as metabolic by-products requiring a finely tuned homeostasis (Figure 4)
Summary
Reduction-oxidation (redox) processes are a major consequence of the presence of ground-state oxygen gas (O2, constituting c.a. 20.8% of the atmosphere) as a natural oxidant on Earth. Due to low photosynthetic metabolism in fruit, one could predict different contributions than for leaves, which further depends on the plant species that exhibit diverse biochemical pathways able to scavenge and process cellular ROS.
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