Tocopherols mutual balance is a key player for maintaining Arabidopsis thaliana growth under salt stress

Abstract

Enhanced channeling carbon through pathways: shikimate/chorismate, benzenoid-phenylopropanoid or 2-C-methyl-D-erythritol 4-phosphate (MEP) provides a multitude of secondary metabolites and cell wall components and allows plants response to environmental stresses. Through the biosynthetic pathways, different secondary metabolites, like tocopherols (TCs), are bind to mutual dependencies and metabolic loops, that are not yet fully understood. We compared, in parallel, the influence of α- and γ-TCs on metabolites involved in osmoprotective/antioxidative response, and physico-chemical modification of plasma membrane and cell wall. We studied Arabidopsis thaliana Columbia ecotype (WT), mutant vte1 deficient in α- and γ-TCs, mutant vte4 over-accumulating γ-TC instead of α-TC, and transgenic line tmt over-accumulating α-TC; exposed to NaCl. The results indicate that salt stress activates β-carboxylation processes in WT plants and in plants with altered TCs accumulation. In α-TC-deficient plants, NaCl causes ACC decrease, but does not change SA, whose concentration remains higher than in α-TC accumulating plants. α/γ-TCs contents influence carbohydrates, poliamines, phenolic (caffeic, ferrulic, cinnamic) acids accumulation patterns. Salinity results in increased detection of the LM5 galactan and LM19 homogalacturonan epitopes in α-TC accumulating plants, and the LM6 arabinan and MAC207 AGP epitopes in α-TC deficient mutants. Parallel, plants with altered TCs composition show decreased both the cell turgor and elastic modulus determined at the individual cell level. α-TC deficient plants reveal lower values of cell turgor and elastic modulus, but higher cell hydraulic conductivity than α-TC accumulating plants. Under salt stress, α-TC shows stronger regulatory effect than γ-TC through the impact on chloroplastic biosynthetic pathways and ROS/osmotic-modulating compounds.

Keywords: Arabinogalactan protein and pectic epitopes; Carbohydrates; Elastic modulus of cell wall; Hydraulic conductivity of plasma membranes and turgor pressure; Phenolic compounds; Poliamines; α- and γ-tocopherols.