Specific Roles of α- and γ-Tocopherol in Abiotic Stress Responses of Transgenic Tobacco

Abstract

Tocopherols are lipophilic antioxidants that are synthesized exclusively in photosynthetic organisms. In most higher plants, a-and g-tocopherol are predominant with their ratio being under spatial and temporal control. While a-tocopherol accumulates predominantly in photosynthetic tissue, seeds are rich in g-tocopherol. To date, little is known about the specific roles of a-and g-tocopherol in different plant tissues. To study the impact of tocopherol composition and content on stress tolerance, transgenic tobacco (Nicotiana tabacum) plants constitutively silenced for homogentisate phytyltransferase (HPT) and g-tocopherol methyltransferase (g-TMT) activity were created. Silencing of HPT lead to an up to 98% reduction of total tocopherol accumulation compared to wild type. Knockdown of g-TMT resulted in an up to 95% reduction of a-tocopherol in leaves of the transgenics, which was almost quantitatively compensated for by an increase in g-tocopherol. The response of HPT and g-TMT transgenics to salt and sorbitol stress and methyl viologen treatments in comparison to wild type was studied. Each stress condition imposes oxidative stress along with additional challenges like perturbing ion homeostasis, desiccation, or disturbing photochemistry, respectively. Decreased total tocopherol content increased the sensitivity of HPT:RNAi transgenics toward all tested stress conditions, whereas g-TMT-silenced plants showed an improved performance when challenged with sorbitol or methyl viologen. However, salt tolerance of g-TMT transgenics was strongly decreased. Membrane damage in g-TMT transgenic plants was reduced after sorbitol and methyl viologen-mediated stress, as evident by less lipid peroxidation and/or electrolyte leakage. Therefore, our results suggest specific roles for a-and g-tocopherol in vivo.

Modeling of Dolichol Mass Spectra Isotopic Envelopes as a Tool to Monitor Isoprenoid Biosynthesis

“…The consumption of reducing equivalents by the MEP pathway is more efficient than by MVA (3 versus 2 mol of NADPH is used to produce 1 mol of IPP, respectively; Gruchattka et al, 2013). Finally, an enhanced demand for MEP-derived products, such as the antioxidants tocopherols and carotenoids and/or the phytohormone ABA, also could provide the driving force for the induction of this pathway (Abbasi et al, 2007).…”

Irrigation with Diluted Seawater Improves the Nutritional Value of Cherry Tomatoes

“…This is presumably mediated by the higher in vivo lipid antioxidant activity of γ-tocopherol, which reduced the extent of lipid oxidative membrane damage and pigment loss following oxidative stress in transgenic tobacco plants silenced for γ-tocopherol methyltransferase (γ-TMT). Anyway, γ-tocopherol might not be able to influence cellular signaling like R-tocopherol does and to substitute the latter to ensure a better plant survival in salt stress conditions (27). According to these authors, R-tocopherol appears to provide a better protection of macromolecules from salt-induced denaturation than γ-tocopherol.…”

“…Also, wild-type tobacco plants displayed a >6-fold increase in total tocopherol content from around 70 ng cm 2 in the controls to about 400 ng cm 2 in 400 mM NaCl treated plants (27). The total tocopherol content was closely correlated with the concentration of sodium chloride in the growing medium, with R-tocopherol contributing to >90% of the tocopherol pool (27). Like photosynthetic tissues, tomato berries (6) accumulate predominantly R-tocopherol (Figure 4), whereas tobacco seeds are rich in γ-tocopherol (27).…”

Wild edible plants: Nutritional and toxicological characteristics, retrieval strategies and importance for today's society

“…These strong antioxidants halt the lipid peroxidation chain reaction through donation of the chromanol ring phenolic hydrogen, thus maintain the integrity of the long-chain PUFA of the cell membranes (Niki, 2014). These antioxidants are involved in the non-enzymatic plant protection mechanism against the abiotic stress-induced oxidative damage, being synthesized in response to these adverse conditions (Abbasi et al, 2007;Pinela et al, 2016a). In humans, vitamin E plays a vital role in the fight against various diseases and health conditions such as oxidative stress, inflammatory and degenerative processes, cardiovascular disease and different types of cancer, mainly due to its antioxidant capacity (Galli et al, 2017;Niki, 2014).…”