Characterization of an Arabidopsis mutant deficient in γ-tocopherol methyltransferase
2003
Bergmuller, E. | Porfirova, S. | Dormann, P.
Alpha-tocopherol (vitamin E) is synthesized from γ-tocopherol in chloroplasts by γ-tocopherol methyltransferase (γ-TMT; VTE4). Leaves of many plant species including Arabidopsis contain high levels of α-tocopherol, but are low in γ-tocopherol. To unravel the function of different forms of tocopherol in plants, an Arabidopsis plant (vte4-1) carrying a functional null mutation in the gene γ-TMT was isolated by screening a mutant population via thin-layer chromatography. A second mutant allele (vte4-2) carrying a T-DNA insertion in the coding sequence of γ-TMT was identified in a T-DNA tagged mutant population. In vte4-1 and vte4-2 leaves, high levels of γ-tocopherol accumulated, whereas α-tocopherol was absent indicating that, presumably, these two mutants represents null alleles. Over-expression of the γ-TMT cDNA in vte4-1 restored wild-type tocopherol composition. Mutant plants were very similar to wild type. During oxidative stress (high light, high temperature, cold treatment) the amounts of α-tocopherol and γ-tocopherol increased in wild type, and γ-tocopherol in vte4-1. However, chlorophyll content and photosynthetic quantum yield were very similar in wild type and vte4-1, suggesting that α-tocopherol can be replaced by γ-tocopherol in vte4-1 to protect the photosynthetic apparatus against oxidative stress. Fatty acid and lipid composition were very similar in WT, vte4-1 and vte1, an Arabidopsis mutant previously isolated which is completely devoid of tocopherol. Therefore, a shift in tocopherol composition or the absence of tocopherol has no major impact on the amounts of specific fatty acids or on lipid hydrolysis.
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