Articles
ASCORBIC ACID ACCUMULATION, BIOSYNTHESIS AND RECYCLING DURING TOMATO FRUIT RIPENING
Article number
939_33
Pages
255 – 261
Language
English
Abstract
L-Ascorbic acid (AsA, vitamin C), is known for its vital role in plant antioxidant stress defence metabolism and for its important nutritional and health benefits for the consumer.
In the last decade, studies on plant AsA biosynthesis and metabolism in several plant species have indicated that biosynthesis proceeds primarily via a pathway involving L-galactose.
Alternative biosynthetic routes utilizing myo-inositol, D-galacturonate, and/or GDP-L-gulose have also been suggested, but their potential contribution in planta still has to be clarified.
However, our understanding of the genetic factors underlying the regulation or accumulation of AsA in plant species and different tissues particularly fruit during development is still far from complete.
In principle these differences could be due to variations in the relative AsA biosynthetic capacities, the rate of degradation and/or the capacity for AsA regeneration.
The aim of the present work therefore was to determine the relative contribution of these different processes in fruit of two tomato cultivars differing substantially in their AsA contents (Santorini and Ailsa Craig). Feeding experiments with nonlabelled and radiolabelled precursors of AsA biosynthesis were carried out at different ripening stages and these data compared to the changes in fruit AsA contents, and the activities of key related enzyme activities.
Results demonstrate that fruit AsA contents vary significantly between these cultivars throughout ripening and that the observed differences between the genotypes can at least partly be explained by the differences in the relative biosynthetic and recycling capacities of the tissues.
Interestingly though, the cultivar with the higher AsA and glutathione (GSH) contents exhibits a greater capacity for AsA recycling, but a lower rate of AsA biosynthesis.
These data support the importance of AsA-GSH recycling pathway in maintenance of AsA pools, and indicates the possible existence of feedback control of AsA biosynthesis during ripening.
In the last decade, studies on plant AsA biosynthesis and metabolism in several plant species have indicated that biosynthesis proceeds primarily via a pathway involving L-galactose.
Alternative biosynthetic routes utilizing myo-inositol, D-galacturonate, and/or GDP-L-gulose have also been suggested, but their potential contribution in planta still has to be clarified.
However, our understanding of the genetic factors underlying the regulation or accumulation of AsA in plant species and different tissues particularly fruit during development is still far from complete.
In principle these differences could be due to variations in the relative AsA biosynthetic capacities, the rate of degradation and/or the capacity for AsA regeneration.
The aim of the present work therefore was to determine the relative contribution of these different processes in fruit of two tomato cultivars differing substantially in their AsA contents (Santorini and Ailsa Craig). Feeding experiments with nonlabelled and radiolabelled precursors of AsA biosynthesis were carried out at different ripening stages and these data compared to the changes in fruit AsA contents, and the activities of key related enzyme activities.
Results demonstrate that fruit AsA contents vary significantly between these cultivars throughout ripening and that the observed differences between the genotypes can at least partly be explained by the differences in the relative biosynthetic and recycling capacities of the tissues.
Interestingly though, the cultivar with the higher AsA and glutathione (GSH) contents exhibits a greater capacity for AsA recycling, but a lower rate of AsA biosynthesis.
These data support the importance of AsA-GSH recycling pathway in maintenance of AsA pools, and indicates the possible existence of feedback control of AsA biosynthesis during ripening.
Authors
I. Mellidou, J. Keulemans, M.W. Davey, A. Kanellis
Keywords
vitamin C, biosynthesis, ascorbate-glutathione cycle, Solanum lycopersicum, radiolabelling, enzyme activities
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