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Eukaryotic Cell, November 2009, p. 1648-1657, Vol. 8, No. 11
1535-9778/09/$08.00+0     doi:10.1128/EC.00124-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Replacement of {alpha}-Tocopherol by β-Tocopherol Enhances Resistance to Photooxidative Stress in a Xanthophyll-Deficient Strain of Chlamydomonas reinhardtii{triangledown}

Anchalee Sirikhachornkit, Jai W. Shin,{dagger} Irene Baroli,{ddagger} and Krishna K. Niyogi*

Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102

Received 30 April 2009/ Accepted 21 August 2009

Tocopherols (vitamin E) comprise a class of lipid-soluble antioxidants synthesized only in plants, algae, and some cyanobacteria. The majority of tocopherols in photosynthetic cells is in the {alpha} form, which has the highest vitamin E activity in humans, whereas the β, {gamma}, and {delta} forms normally account for a small percentage of total tocopherols. The antioxidant activities of these forms of tocopherol differ depending on the experimental system, and their relative activities in vivo are unclear. In a screen for suppressors of the xanthophyll-deficient npq1 lor1 double mutant of Chlamydomonas reinhardtii, we isolated a vte3 mutant lacking {alpha}-tocopherol but instead accumulating β-tocopherol. The vte3 mutant contains a mutation in the homolog of a 2-methyl-6-phytyl-1,4-benzoquinone methyltransferase gene found in plants. The vte3 npq1 lor1 triple mutant with β-tocopherol survived better under photooxidative stress than did the npq1 lor1 mutant, but the vte3 mutant on its own did not have an obvious phenotype. Following transfer from low light to high light, the triple mutant showed a higher efficiency of photosystem II, a higher level of cell viability, and a lower level of lipid peroxide, a marker for oxidative stress, than did the npq1 lor1 mutant. After high-light transfer, the level of the photosystem II reaction center protein, D1, was also higher in the vte3 npq1 lor1 mutant, but the rate of D1 photodamage was not significantly different from that of the npq1 lor1 mutant. Taken together, these results suggest that the replacement of {alpha}-tocopherol by β-tocopherol in a xanthophyll-deficient strain of Chlamydomonas reinhardtii contributes to better survival under conditions of photooxidative stress.

* Corresponding author. Mailing address: Department of Plant and Microbial Biology, University of California, 111 Koshland Hall, Berkeley, CA 94720-3102. Phone: (510) 643-6602. Fax: (510) 642-4995. E-mail: niyogi{at}nature.berkeley.edu

{triangledown} Published ahead of print on 28 August 2009.

{dagger} Present address: University of Maryland Baltimore College of Dental Surgery, 650 West Baltimore Street, Baltimore, Maryland 21201.

{ddagger} Present address: IPAustralia, P.O. Box 200, Woden ACT 2606, Australia.

Eukaryotic Cell, November 2009, p. 1648-1657, Vol. 8, No. 11
1535-9778/09/$08.00+0     doi:10.1128/EC.00124-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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