Shading the whole vines during young fruit development decreases ascorbate accumulation in kiwi

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Abstract
We investigated how different lighting conditions affected the levels of ascorbate (AsA), sugar contents, the mRNA expression of genes involved in AsA biosynthesis and recycling and enzyme activity in kiwi fruits. Shaded leaves had dramatically less AsA as well as altered transcript levels and enzyme activities. In contrast, fruits that had been covered directly at various developmental stages showed no changes in those parameters. Fruits had significantly less AsA content before 40 days after anthesis (DAA) when whole vines were shaded only from 0 to 40 DAA, whereas transcript levels of most related genes (except those for GDP-L-galactose-1-phosphate phosphorylase and GDP-mannose pyrophosphorylase) followed a parallel trend. When the shading was removed after 40 DAA, values for the ripening fruits returned to those measured for the control. Such a response, however, was not observed when shading treatments were delayed until after 40 DAA. Fruits were also smaller at harvest when vines were shaded at the earliest time point. The present results suggest that lighting conditions can indirectly affect the capacity of biosynthesis and recycling of AsA in young fruits of kiwi, and this regulation might occur via the interaction of signal from leaves and development of fruit.

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