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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Tocotrienols, the Unsaturated Forms of Vitamin E, Can Function as Antioxidants and Lipid Protectors in Tobacco Leaves^[W]

Commissariat à l'Energie Atomique/Grenoble, Institut de Recherches en Technologies et Sciences pour le Vivant, Laboratoire de Physiologie Cellulaire Végétale, F–38054 Grenoble cedex 9, France (M.M.); Commissariat à l'Energie Atomique, Direction des Sciences du Vivant, Institut de Biologie Environnementale et de Biotechnologie, Laboratoire d'Ecophysiologie Moléculaire des Plantes, 13108 Saint-Paul-lez-Durance, France (B.K., P.R., M.H.); CNRS, UMR Biologie Végétale et Microbiologie Environnementales, 13108 Saint-Paul-lez-Durance, France (B.K., P.R., M.H.); and Université Aix-Marseille, 13108 Saint-Paul-lez-Durance, France (B.K., P.R., M.H.)

Vitamin E is a generic term for a group of lipid-soluble antioxidant compounds, the tocopherols and tocotrienols. While tocotrienols are considered as important vitamin E components in humans, with functions in health and disease, the protective functions of tocotrienols have never been investigated in plants, contrary to tocopherols. We took advantage of the strong accumulation of tocotrienols in leaves of double transgenic tobacco (Nicotiana tabacum) plants that coexpressed the yeast (Saccharomyces cerevisiae) prephenate dehydrogenase gene (PDH) and the Arabidopsis (Arabidopsis thaliana) hydroxyphenylpyruvate dioxygenase gene (HPPD) to study the antioxidant function of those compounds in vivo. In young leaves of wild-type and transgenic tobacco plants, the majority of vitamin E was stored in thylakoid membranes, while plastoglobules contained mainly -tocopherol, a very minor component of vitamin E in tobacco. However, the vitamin E composition of plastoglobules was observed to change substantially during leaf aging, with -tocopherol becoming the major form. Tocotrienol accumulation in young transgenic HPPD-PDH leaves occurred without any significant perturbation of photosynthetic electron transport. Tocotrienols noticeably reinforced the tolerance of HPPD-PDH leaves to high light stress at chilling temperature, with photosystem II photoinhibition and lipid peroxidation being maintained at low levels relative to wild-type leaves. Very young leaves of wild-type tobacco plants turned yellow during chilling stress, because of the strongly reduced levels of chlorophylls and carotenoids, and this phenomenon was attenuated in transgenic HPPD-PDH plants. While sugars accumulated similarly in young wild-type and HPPD-PDH leaves exposed to chilling stress in high light, a substantial decrease in tocotrienols was observed in the transgenic leaves only, suggesting vitamin E consumption during oxygen radical scavenging. Our results demonstrate that tocotrienols can function in vivo as efficient antioxidants protecting membrane lipids from peroxidation.

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.117614

^* Corresponding author; e-mail michel.havaux{at}cea.fr.

Received February 25, 2008; accepted April 18, 2008; published April 25, 2008.