JXB Advance Access first published online on June 22, 2007
This version published online on August 11, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm124
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Light regulation of ascorbate biosynthesis is dependent on the photosynthetic electron transport chain but independent of sugars in Arabidopsis
1Department of Advanced Bioscience, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara, 631-8505 Japan
2Department of Food and Nutritional Science, College of Bioscience and Biotechnology, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi, 487-8501 Japan
3Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane, 690-8504 Japan
To whom correspondence should be addressed. E-mail: shigeoka{at}nara.kindai.ac.jp
It has been known that leaves exposed to high light contain more L-ascorbic acid (AsA) than those in the shade. However, the mechanism of the light regulation of the AsA pool size in plants is largely unknown. In this work, the relationship between gene expression levels related to AsA biosynthesis and photosynthesis have been studied. When 2-week-old Arabidopsis plants grown under a 16 h daily photoperiod were moved into the dark, the AsA level in the leaves was decreased by 91% in 72 h, whereas it increased by 171% in the leaves of plants exposed to continuous light during the same period. Among the several enzymes of the AsA biosynthesis pathway, the transcript levels of GDP-D-mannose pyrophosphorylase, L-galactose 1-P phosphatase, L-galactono-1,4-lactone dehydrogenase, and the VTC2 gene were down-regulated in the dark. Treatment with inhibitors of photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and atrazine, arrested a rise in the AsA pool size accompanying the decrease in the transcript levels of the genes of the above enzyme in the leaves. When the plants were transferred to a medium containing 0.5% (w/v) sucrose, the photosynthesis activities and the leaf AsA levels were lowered even under exposure to light compared with those in plants on the medium without sucrose. In contrast, the AsA level in leaves of the sugar-insensitive Arabidopsis mutant abi4/sun6 was unaffected by external sucrose. No significant difference in the expression profiles for AsA biosynthesis enzymes was observed between the wild-type and mutant plants by sucrose feeding. The results suggest that photosynthetic electron transport of chloroplasts is closely related to AsA pool size regulation in leaves.
Key words: Arabidopsis thaliana, ascorbate, abi4/sun6 mutant, sugar, photosynthesis
* These authors contributed equally to this work.
This is a new version of Open Access Copyright line.
Received 15 December 2006; Revised 25 April 2007 Accepted 10 May 2007
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