Plant Cell Advance Online Publication
Published on September 29, 2006; 10.1105/tpc.105.039404
Received November 14, 2005
Returned for revision July 27, 2006
Accepted August 24, 2006
Tocopherols Play a Crucial Role in Low-Temperature Adaptation and Phloem Loading in Arabidopsis
Hiroshi Maeda 1, Wan Song 2, Tammy L. Sage 3, and Dean DellaPenna 4*
1 Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824; Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824; Cell and Molecular Biology Program, Michigan State University, East Lansing, Michigan 48824
2 Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824; Genetics Program, Michigan State University, East Lansing, Michigan 48824
3 Department of Botany, University of Toronto, Toronto, Ontario, Canada M5S 3B2
4 Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824; Cell and Molecular Biology Program, Michigan State University, East Lansing, Michigan 48824; Genetics Program, Michigan State University, East Lansing, Michigan 48824
* To whom correspondence should be addressed. E-mail: dellapen{at}msu.edu.
To test whether tocopherols (vitamin E) are essential in the protection against oxidative stress in plants, a series of Arabidopsis thaliana vitamin E (vte) biosynthetic mutants that accumulate different types and levels of tocopherols and pathway intermediates were analyzed under abiotic stress. Surprisingly subtle differences were observed between the tocopherol-deficient vte2 mutant and the wild type during high-light, salinity, and drought stresses. However, vte2, and to a lesser extent vte1, exhibited dramatic phenotypes under low temperature (i.e., increased anthocyanin levels and reduced growth and seed production). That these changes were independent of light level and occurred in the absence of photoinhibition or lipid peroxidation suggests that the mechanisms involved are independent of tocopherol functions in photoprotection. Compared with the wild type, vte1 and vte2 had reduced rates of photoassimilate export as early as 6 h into low-temperature treatment, increased soluble sugar levels by 60 h, and increased starch and reduced photosynthetic electron transport rate by 14 d. The rapid reduction in photoassimilate export in vte2 coincides with callose deposition exclusively in phloem parenchyma transfer cell walls adjacent to the companion cell/sieve element complex. Together, these results indicate that tocopherols have a more limited role in photoprotection than previously assumed but play crucial roles in low-temperature adaptation and phloem loading.
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