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Published on April 25, 2008; 10.1104/pp.108.117614

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Received February 25, 2008
Accepted April 18, 2008

Tocotrienols, the unsaturated forms of vitamin E, can function as antioxidants and lipid protectors in tobacco leaves

Michel Matringe , Brigitte Ksas , Pascal Rey , and Michel Havaux *

CEA/Grenoble, iRTSV, Laboratoire de Physiologie Cellulaire Vegetale, 17 rue des Martyrs, F-38054 Grenoble cedex 9, France ; CEA, DSV, iBEB, Laboratoire d'Ecophysiologie Moleculaire des Plantes, 13108 Saint-Paul-lez-Durance, France, and CNRS, UMR Biologie Vegetale et Microbiologie Environnementales, 13108 Saint-Paul-lez-Durance, France, and Universite Aix-Marseille, 13108 Saint-Paul-lez-Durance, France

* Corresponding author; email: michel.havaux{at}cea.fr.

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 plants that co-expressed the yeast prephenate dehydrogenase gene (PDH) and the Arabidopsis hydroxyphenylpyruvate dioxygenase gene (HPPD) to study in vivo the antioxidant function of those compounds. In young leaves of wild-type and transgenic tobacco plants, the majority of vitamin E was stored in thylakoid membranes, while plastoglobules contained mainly {delta}-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 {alpha}-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 PSII photoinhibition and lipid peroxidation being maintained low relative to wild-type leaves. Very young leaves of wild-type tobacco plants turned yellow during chilling stress, because of a strongly reduced level of chlorophylls and carotenoids, and this phenomenon was attenuated in transgenic HPPD-PDH plants. While sugars accumulated similarly in young WT 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 oxy-radical scavenging. Our results demonstrate that tocotrienols can function in vivo as efficient antioxidants protecting membrane lipids from peroxidation.






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