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Synthesis of L-ascorbic acid in the phloem
Robert D Hancock1, Diane McRae, Sophie Haupt
1Unit of Plant Biochemistry, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom. rhanco@scri.sari.ac.uk
BMC Plant Biology
|November 25, 2003
Summary
Plants synthesize vitamin C (L-ascorbic acid or AsA) in their phloem. This discovery reveals a new pathway for AsA distribution within plants and its accumulation in storage organs.
Area of Science:
- Plant Physiology
- Biochemistry
- Nutritional Science
Background:
- Plants are the primary dietary source of vitamin C (L-ascorbic acid, AsA).
- Mechanisms of AsA synthesis and regulation in plants are not fully understood.
- Variability in AsA content in plant storage organs remains unexplained.
Purpose of the Study:
- To investigate the possibility of AsA synthesis within plant phloem.
- To understand the role of phloem in AsA distribution within plants.
Main Methods:
- Aphid stylectomy and histochemical analysis to detect AsA in phloem sap.
- Enzyme activity assays in phloem exudates.
- Demonstration of AsA biosynthesis in isolated phloem strands using labeled precursors.
- Phloem uptake studies using radiolabeled intermediates and AsA in leaf discs.
Main Results:
- Evidence for AsA presence in the phloem sap of various crop species was found.
- Enzymes of the primary AsA biosynthetic pathway were detected in phloem exudates.
- AsA biosynthesis was confirmed in isolated phloem strands.
- Phloem demonstrated uptake of AsA pathway intermediates and AsA itself.
Conclusions:
- Active AsA biosynthesis occurs within the plant phloem.
- Phloem AsA synthesis is a crucial factor in whole-plant AsA distribution.
- Further research is needed to identify in vivo substrates and the contribution of phloem synthesis to storage organ AsA accumulation.