α-Tocopherol deficiency disrupts xanthophyll-cycle-dependent NPQ and high-light acclimation in Arabidopsis

Plants exposed to high light (HL) must dissipate excess excitation energy while preventing photooxidative damage to the photosynthetic apparatus. Tocopherols are major lipophilic antioxidants in chloroplasts, but whether replacement of α-tocopherol by γ-tocopherol preserves HL acclimation and NPQ-associated photoprotection remains unclear. Here, we investigated the response of Arabidopsis wild-type Col and the α-tocopherol-deficient mutant vte4-4, which accumulates γ-tocopherol instead of α-tocopherol, to acute HL stress. Under HL, vte4-4 showed more severe visible leaf damage than Col, together with higher malondialdehyde and jasmonic acid accumulation and a significant loss in the PSII reaction center protein D1. The mutant also displayed weaker induction of non-photochemical quenching (NPQ), stronger decreases in Fv/Fm and ΦEo, and more pronounced alterations in OJIP-derived parameters due to HL stress. Although vte4-4 increased the total VAZ pool under HL, its lower Z/(VAZ) and higher A/(VAZ) ratios respect to Col indicate a qualitative impairment in xanthophyll-cycle operation rather than defective pigment accumulation. This phenotype was associated with lower HL-induced PsbS accumulation, loss of VDE protein and low AsA/DHA ratio, suggesting a redox limitation affecting both photooxidative buffering and VDE-dependent zeaxanthin formation. Together, our results indicate that γ-tocopherol accumulation is not sufficient to sustain wild-type-like HL acclimation in the absence of α-tocopherol. We propose that α-tocopherol functions not only as a membrane antioxidant, but also as a component of the photoprotective network that supports efficient NPQ engagement and preserves PSII performance under high light stress.