Abstract
Ascorbic acid (AsA) is an essential multifaceted phytonutrient for both the human diet and plant growth. Optimum levels of AsA accumulation combined with balanced redox homeostasis are required for normal plant development and defense response to adverse environmental stimuli. Notwithstanding its moderate AsA levels, tomatoes constitute a good source of vitamin C in the human diet. Therefore, the enhancement of AsA levels in tomato fruit attracts considerable attention, not only to improve its nutritional value but also to stimulate stress tolerance. Genetic regulation of AsA concentrations in plants can be achieved through the fine-tuning of biosynthetic, recycling, and transport mechanisms; it is also linked to changes in the whole fruit metabolism. Emerging evidence suggests that tomato synthesizes AsA mainly through the l-galactose pathway, but alternative pathways through d-galacturonate or myo-inositol, or seemingly unrelated transcription and regulatory factors, can be also relevant in certain developmental stages or in response to abiotic factors. Considering the recent advances in our understanding of AsA regulation in model and other non-model species, this review attempts to link the current consensus with novel technologies to provide a comprehensive strategy for AsA enhancement in tomatoes, without any detrimental effect on plant growth or fruit development.
Highlights
Vitamin C or ascorbic acid (AsA) is one of the most abundant water-soluble antioxidant molecules, essential for aerobic life, presents in most living organisms, including plants, animals, fungi, and protozoa [1,2,3,4]
Other primates, and a few other mammals including guinea pigs, and certain groups of bats and birds, have lost the ability to synthesize this low molecular weight molecule as a result of mutations in the coding sequence of GuLO [4,6]. This loss of capacity may serve as an evolutionary step towards the regulation of human cell redox homeostasis since the reaction catalyzed by GuLO in the biosynthetic pathway generates hydrogen peroxide (H2O2), a toxic Reactive Oxygen Species (ROS) that could eliminate the advantage of AsA biosynthesis [7]
The accumulation of AsA in this line is approximately 40% higher compared to M82, probably as a result of the enhanced metabolic flux through the D-galacturonate pathway, which is driven by cell wall and pectin degradation triggered by ethylene during the ripening process [58,59]
Summary
Vitamin C (vitC) or ascorbic acid (AsA) is one of the most abundant water-soluble antioxidant molecules, essential for aerobic life, presents in most living organisms, including plants, animals, fungi, and protozoa [1,2,3,4]. Other primates, and a few other mammals including guinea pigs, and certain groups of bats and birds, have lost the ability to synthesize this low molecular weight molecule as a result of mutations in the coding sequence of GuLO [4,6]. This loss of capacity may serve as an evolutionary step towards the regulation of human cell redox homeostasis since the reaction catalyzed by GuLO in the biosynthetic pathway generates hydrogen peroxide (H2O2), a toxic Reactive Oxygen Species (ROS) that could eliminate the advantage of AsA biosynthesis [7]. On the basis of these considerations, this review attempts to elucidate recent findings in the genetic factors underlying AsA accumulation in fruit species, focusing on tomato, for improved fruit quality and alleviation of abiotic stress
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