Ascorbate biosynthesis during early fruit development is the main reason for its accumulation in kiwi

Area of Science:

• Plant Physiology
• Biochemistry
• Molecular Biology

Background:

• Ascorbic acid (AsA) is a vital antioxidant and enzyme cofactor in plants.
• Its accumulation control at the expression level, particularly in sink tissues like fruit, remains unclear.
• Kiwifruit (Actinidia) is notable for its exceptionally high ascorbate content.

Purpose of the Study:

• To investigate the primary mechanism of ascorbate accumulation in developing kiwifruit.
• To determine if AsA accumulation results from fruit biosynthesis or import from foliage.
• To analyze the expression patterns of key AsA biosynthesis genes during fruit development.

Main Methods:

• Systematic investigation of AsA levels, biosynthetic capacity, and gene expression in developing kiwifruit (A. deliciosa cv. Qinmei).
• Monitoring of AsA recycling and localization across different fruit tissues and developmental stages.
• Analysis of gene expression in stem, leaf petioles, and fruit tissues.

Main Results:

• AsA content peaked at 30 days after anthesis (DAA), correlating with increased biosynthesis and decreased recycling.
• Expression of most AsA biosynthesis genes mirrored AsA accumulation patterns, with notable exceptions.
• L-galactose-1-phosphate phosphatase (GPP) expression strongly correlated with AsA accumulation rate, while transport into fruit via petioles was not observed.

Conclusions:

• Ascorbate accumulation in kiwifruit during early development is predominantly due to endogenous biosynthesis.
• GPP is identified as a potential key regulator of AsA biosynthesis in kiwifruit.
• GDP-L-galactose-1-phosphate phosphorylase is unlikely to be a major regulatory factor in this process.