Tocopherol metabolism, oxidation and recycling under high light stress in Arabidopsis

Summary Tocopherols are synthesized and accumulated by all plants and many cyanobacteria. The quenching and scavenging of reactive oxygen species and lipid peroxy radicals by tocopherols can result in the formation of various tocopherol oxidation compounds. A targeted GC/MS profiling method was developed to quantify all tocopherols and pathway intermediates, and 23 potential α‐ and γ‐tocopherol oxidation products. This method was used to study the response of wild‐type Arabidopsis (Col) and the tocopherol biosynthetic mutants vte1 , vte2 and vte4 during 12 h low‐ and high‐light treatments (LL and HL, 90 and 1500 μmol photon m −2  sec −1 , respectively) and a subsequent 12 h dark recovery period. All tocopherols and pathway intermediates exhibited HL‐dependent increases except 2,3‐dimethyl‐6‐phytyl‐1,4‐benzoquinone (DMPBQ) in vte1 and β‐tocopherol in Col. Profiling of potential tocopherol oxidation products during HL treatment indicated the presence of only α‐tocopherolquinol (α‐TQH 2 ) in Col and only γ‐tocopherolquinol (γ‐TQH 2 ) in vte4 , both of which accumulated to similar levels and with similar kinetics the two genotypes. However, during dark recovery, the level of α‐TQH 2 in Col decreased several times faster than that of γ‐TQH 2 in vte4 , suggesting the presence of biochemical processes with higher specificity for α‐TQH 2 . 14 C‐labeled α‐tocopherolquinone (α‐TQ) applied to isolated Col chloroplasts was converted to 14 C‐α‐tocopherol, demonstrating the existence of a plastid‐based system for recycling oxidized α‐tocopherol. The accumulation of 14 C‐trimethylphytylbenzoquinone (TMPBQ) by isolated vte1 plastids treated with 14 C‐labeled α‐TQ is consistent with the tocopherolquinone‐recycling pathway utilizing a yet to be identified plastid‐localized dehydratase that converts tocopherolquinone to TMPBQ.