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BIOSYNTHESIS OF ASCORBIC ACID IN PLANTS: A Renaissance.
Nicholas Smirnoff1, Patricia L Conklin, Frank A Loewus
1School of Biological Sciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter, EX4 4PS, United Kingdom; e-mail: N.Smirnoff@exeter.ac.uk, Boyce Thompson Institute for Plant Research at Cornell University, Tower Road, Ithaca, NY 14853; e-mail: plc3@cornell.edu, Institute of Biological Chemistry, Washington State University, P.O. Box 646340, Pullman, WA 99164-6340;
Annual Review of Plant Physiology and Plant Molecular Biology
|May 5, 2001
Summary
Scientists have uncovered the plant biosynthesis pathway for L-ascorbic acid (vitamin C), a crucial antioxidant. This discovery clarifies how plants produce vitamin C, differing from mammalian routes.
Area of Science:
- Biochemistry
- Plant Science
- Molecular Biology
Background:
- L-ascorbic acid (vitamin C) is a vital antioxidant, yet its plant biosynthesis pathway remained largely unknown for decades.
- Early studies indicated plant vitamin C production differs significantly from mammalian pathways.
- The identification of an Arabidopsis thaliana mutant in 1996 spurred new research into plant ascorbic acid biosynthesis.
Purpose of the Study:
- To elucidate the previously elusive biosynthetic pathway of L-ascorbic acid in plants.
- To identify key intermediates and enzymes involved in plant vitamin C production.
- To provide a foundation for future research on ascorbate metabolism and its physiological roles in plants.
Main Methods:
- Utilized radioisotopic labeling studies to trace metabolic pathways.
- Employed biochemical and molecular genetic evidence, including the analysis of Arabidopsis thaliana mutants.
- Investigated enzymes responsible for the final conversion steps in the pathway.
Main Results:
- A novel plant ascorbic acid biosynthesis pathway was discovered, distinct from the mammalian route.
- Key intermediates identified include GDP-D-mannose, L-galactose, and L-galactono-1,4-lactone.
- The terminal enzyme converting L-galactono-1,4-lactone to ascorbate has been a focus of research.
Conclusions:
- The newly discovered pathway provides a comprehensive understanding of plant vitamin C biosynthesis.
- Further research on related enzymes, mutants, and comparative studies in algae and fungi will deepen insights.
- Understanding the biosynthetic pathway will accelerate research into the control and physiological functions of ascorbate in plants.