Tocochromanol functions in plants: antioxidation and beyond

Evaluation of RPLC stationary phases for tocopherol and tocotrienol positional isomer separation: Method development and profiling

Reversed-phase separation of tocopherols (Ts) and tocotrienols (Ts) using C18 stationary phases results in the coelution of β and γ positional isomers, leading to identification errors. This study investigates the potential of alternative stationary phase chemistries to effectively resolve tocochromanols, specifically focusing on the critical pair of β and γ positional isomers. Initial screening of seven different stationary phases (C18, C18-PFP, C30, PFP, 5PYE, πNAP, and RP-Amide) was conducted. Linear solvent strength (LSS) studies were performed to assess the impact of the organic modifier (methanol) and temperature on the chromatographic performance parameters. Five columns were found to be suitable for the tocochromanol separation and two different chromatographical conditions per column were proposed. Elution order of tocochromanols was unique for 5PYE, πNAP and C30 columns in comparison to RP-Amide and PFP. Method development for the quantitative analysis of four tocopherol and four tocotrienol homologues was performed. The optimised method employed the RP-Amide (150 × 4.6 mm, 2.6 μm dp) superficially porous particle column, mobile phase of methanol:water of 92:8, v/v, with a flow rate of 1.0 mL/min, column oven temperature of 40 °C and fluorescence detection (λex 295 nm, λem 330 nm). The analysis run time was 10.5 min with 13.6 MPa back pressure. The method was validated and the obtained LOQs were found to be 1.30-3.13 μg/mL. The method developed was successfully applied for the determination of tocochromanols in twenty samples with unique tocochromanol profiles. Principal component analysis illustrated three distinct groups based on the tocochromanol profile.

Complexity of responses to ionizing radiation in plants, and the impact on interacting biotic factors

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

Overexpression of tocopherol biosynthesis genes in guayule (Parthenium argentatum) reduces rubber, resin and argentatins content in stem and leaf tissues

Natural rubber produced in stems of the guayule plant (Parthenium argentatum) is susceptible to post-harvest degradation from microbial or thermo-oxidative processes, especially once stems are chipped. As a result, the time from harvest to extraction must be minimized to recover high quality rubber, especially in warm summer months. Tocopherols are natural antioxidants produced in plants through the shikimate and methyl-erythtiol-4-phosphate (MEP) pathways. We hypothesized that increased in vivo guayule tocopherol content might protect rubber from post-harvest degradation, and/or allow reduced use of chemical antioxidants during the extraction process. With the objective of enhancing tocopherol content in guayule, we overexpressed four Arabidopsis thaliana tocopherol pathway genes in AZ-2 guayule via Agrobacterium-mediated transformation. Tocopherol content was increased in leaf and stem tissues of most transgenic lines, and some improvement in thermo-oxidative stability was observed. Overexpression of the four tocopherol biosynthesis enzymes, however, altered other isoprenoid pathways resulting in reduced rubber, resin and argentatins content in guayule stems. The latter molecules are mainly synthesized from precursors derived from the mevalonate (MVA) pathway. Our results suggest the existence of crosstalk between the MEP and MVA pathways in guayule and the possibility that carbon metabolism through the MEP pathway impacts rubber biosynthesis.

Coordinated Transcriptome and Metabolome Analyses of a Barley hvhggt Mutant Reveal a Critical Role of Tocotrienols in Endosperm Starch Accumulation

Tocotrienols and tocopherols (vitamin E) are potent antioxidants that are synthesized in green plants. Unlike ubiquitous tocopherols, tocotrienols predominantly accumulate in the endosperm of monocot grains, catalyzed by homogentiate geranylgeranyl transferase (HGGT). Previously, we generated a tocotrienol-deficient hvhggt mutant with shrunken barley grains. However, the relationship between tocotrienols and grain development remains unclear. Here, we found that the hvhggt lines displayed hollow endosperms with defective transfer cells and reduced aleurone layers. The carbohydrate and starch contents of the hvhggt endosperm decreased by approximately 20 and 23%, respectively. Weighted gene coexpression network analyses identified a critical gene module containing HvHGGT, which was strongly associated with the hvhggt mutation and enriched with gene functions in starch and sucrose metabolism. Metabolome measurements revealed an elevated soluble sugar content in the hvhggt endosperm, which was significantly associated with the identified gene modules. The hvhggt endosperm had significantly higher NAD(H) and NADP(H) contents and lower levels of ADPGlc (regulated by redox balance) than the wild-type, consistent with the absence of tocotrienols. Interestingly, exogenous α-tocotrienol spraying on developing hvhggt spikes partially rescued starch accumulation and endosperm defects. Our study supports a potential novel function of tocotrienols in grain starch accumulation and endosperm development in monocot crops.

Genetic improvement of tocotrienol content enhances the oxidative stability of canola oil

Background

Tocotrienols and tocopherols, which are synthesized in plastids of plant cells with similar functionalities, comprise vitamin E to serve as a potent lipid-soluble antioxidant in plants. The synthesis of tocopherols involves the condensation of homogentisic acid (HGA) and phytyl diphosphate (PDP) under the catalysis of homogentisate phytyltransferase (HPT). Tocotrienol synthesis is initiated by the condensation of HGA and geranylgeranyl diphosphate (GGDP) mediated by homogentisate geranylgeranyl transferase (HGGT). As one of the most important oil crops, canola seed is regarded as an ideal plant to efficiently improve the production of vitamin E tocochromanols through genetic engineering approaches. However, only a modest increase in tocopherol content has been achieved in canola seed to date.

Methods

In this study, we transformed barley HGGT (HvHGGT) into canola to improve total tocochromanol content in canola seeds.

Results and discussion

The results showed that the total tocochromanol content in the transgenic canola seeds could be maximally increased by fourfold relative to that in wild-type canola seeds. Notably, no negative impact on important agronomic traits was observed in transgenic canola plants, indicating great application potential of the HvHGGT gene in enhancing tocochromanol content in canola in the future. Moreover, the oil extracted from the transgenic canola seeds exhibited significantly enhanced oxidative stability under high temperature in addition to the increase in total tocochromanol content, demonstrating multiple desirable properties of HvHGGT.

Improved production and quality of peppers irrigated with regenerated water by the application of 24-epibrassinolide

Water shortage for crop irrigation is reducing agricultural production worldwide and the use of sewage treatment plant (STP) water to irrigate horticultural fields is a solution to avoid the use of drinkable water in agriculture. In this study, two different genotypes of pepper (Red Cherry Small and Italian green) were irrigated with STP water, as an alternative to potable water. Moreover, the foliar application of a molecule with biostimulant properties (24-epibrassinolide; EBR) was tested as a strategy to ameliorate the production and quality of fruits. Both genotypes differed on their tolerance to the suffered oxidative stress due to their different salinity tolerance, but fruit commercial weight was reduced by 49% on the salt sensitive and by 37% on the salt tolerant. Moreover, ascorbic acid was also decreased by 37% after STP water irrigation in the Red Cherry Small peppers. However, EBR applications alleviated STP watering stress effects improving pepper plants fruit production and quality parameters, such as ascorbic acid and capsaicinoids. These results have important economic and environmental relevance to overcome present and future water deficiencies in the agricultural sector derived from climate change, guaranteeing the maintenance of production in peppers irrigated with STP water for a more sustainable agriculture following relevant circular economy actions.

Vitamin E biofortification: Maximizing oilseed tocotrienol and total vitamin E tocochromanol production by use of metabolic bypass combinations

Vitamin E tocochromanols are generated in plants by prenylation of homogentisate using geranylgeranyl diphosphate (GGDP) for tocotrienol biosynthesis and phytyl diphosphate (PDP) for tocopherol biosynthesis. Homogentisate geranylgeranyl transferase (HGGT), which uses GGDP for prenylation, is a proven target for oilseed tocochromanol biofortification that effectively bypasses the chlorophyll-linked pathway that limits PDP for vitamin E biosynthesis. In this report, we explored the feasibility of maximizing tocochromanol production in the oilseed crop camelina (Camelina sativa) by combining seed-specific HGGT expression with increased biosynthesis and/or reduced homogentisate catabolism. Plastid-targeted Escherichia coli TyrA-encoded chorismate mutase/prephenate dehydrogenase and Arabidopsis hydroxyphenylpyruvate dioxygenase (HPPD) cDNA were co-expressed in seeds to bypass feedback-regulated steps and increase flux into homogentisate biosynthesis. Homogentisate catabolism was also suppressed by seed-specific RNAi of the gene for homogentisate oxygenase (HGO), which initiates homogentisate degradation. In the absence of HGGT expression, tocochromanols were increased by ∼2.5-fold with HPPD/TyrA co-expression, and ∼1.4-fold with HGO suppression compared to levels in non-transformed seeds. No further increase in tocochromanols was observed in HPPD/TyrA lines with the addition of HGO RNAi. HGGT expression alone increased tocochromanol concentrations in seeds by ∼four-fold to ≤1400 μg/g seed weight. When combined with HPPD/TyrA co-expression, we obtained an additional three-fold increase in tocochromanol concentrations indicating that homogentisate concentrations limit HGGT's capacity for maximal tocochromanol production. The addition of HGO RNAi further increased tocochromanol concentrations to 5000 μg/g seed weight, an unprecedented tocochromanol concentration in an engineered oilseed. Metabolomic data obtained from engineered seeds provide insights into phenotypic changes associated with "extreme" tocochromanol production.

How do barley plants with impaired photosynthetic light acclimation survive under high-light stress?

MAIN CONCLUSION

WHIRLY1 deficient barley plants surviving growth at high irradiance displayed increased non-radiative energy dissipation, enhanced contents of zeaxanthin and the flavonoid lutonarin, but no changes in α-tocopherol nor glutathione. Plants are able to acclimate to environmental conditions to optimize their functions. With the exception of obligate shade plants, they can adjust their photosynthetic apparatus and the morphology and anatomy of their leaves to irradiance. Barley (Hordeum vulgare L., cv. Golden Promise) plants with reduced abundance of the protein WHIRLY1 were recently shown to be unable to acclimatise important components of the photosynthetic apparatus to high light. Nevertheless, these plants did not show symptoms of photoinhibition. High-light (HL) grown WHIRLY1 knockdown plants showed clear signs of exposure to excessive irradiance such as a low epoxidation state of the violaxanthin cycle pigments and an early light saturation of electron transport. These responses were underlined by a very large xanthophyll cycle pool size and by an increased number of plastoglobules. Whereas zeaxanthin increased with HL stress, α-tocopherol, which is another lipophilic antioxidant, showed no response to excessive light. Also the content of the hydrophilic antioxidant glutathione showed no increase in W1 plants as compared to the wild type, whereas the flavone lutonarin was induced in W1 plants. HPLC analysis of removed epidermal tissue indicated that the largest part of lutonarin was presumably located in the mesophyll. Since lutonarin is a better antioxidant than saponarin, the major flavone present in barley leaves, it is concluded that lutonarin accumulated as a response to oxidative stress. It is also concluded that zeaxanthin and lutonarin may have served as antioxidants in the WHIRLY1 knockdown plants, contributing to their survival in HL despite their restricted HL acclimation.

α-Tocopherol application as a countermeasure to UV-B stress in bread wheat (Triticum aestivum L.)

The source of energy for all photoautotrophic organisms is light, which is absorbed by photosynthetic processes and used to transform carbon dioxide and H2O into organic molecules. The majority of UV-B light (280 to 320 nm) is absorbed by stratospheric ozone layer, although some of it does reach at the Earth's surface. Because of the sedentary lifestyle of plants, this form of abiotic stress is unavoidable and can induce growth and even cell death. Ten-day-old calli generated from mature Kirik wheat embryos were subjected to UV-B radiation for 0, 2, 4, and 6 h to examine the function of exogenous α-tocopherol, a lipophilic antioxidant, in wheat tolerance to UV-B radiation stress. The calli were then moved to a callus medium containing α-tocopherol (0, 50, and 100 mg/l) and cultivated there for 20 days after being subjected to UV-B stress. For plant regeneration, embryogenic calli were put on a medium for plant regeneration after 30 days. The findings of this investigation demonstrated that an increase in UV-B exposure period resulted in a substantial drop in the relative growth rate of callus, the rate of embryogenic callus, the rate of responding embryogenic callus, and the number of plants in each explant. On the other hand, with the application of α-tocopherol, all these parameters improved, and the best result was observed in the application of 100 mg/l of α-tocopherol in terms of plant regeneration under UV-B stress.

Salt-Induced Modulation of Ion Transport and PSII Photoprotection Determine the Salinity Tolerance of Amphidiploid Brassicas

Brassica species show varying levels of resistance to salt stress. To understand the genetics underlying these differential stress tolerance patterns in Brassicas, we exposed two widely cultivated amphidiploid Brassica species having different genomes, Brassica juncea (AABB, n = 18) and Brassica napus (AACC, n = 19), to elevated levels of NaCl concentration (300 mM, half the salinity of seawater). B. juncea produced more biomass, an increased chlorophyll content, and fewer accumulated sodium (Na+) and chloride (Cl-) ions in its photosynthesizing tissues. Chlorophyll fluorescence assays revealed that the reaction centers of PSII of B. juncea were more photoprotected and hence more active than those of B. napus under NaCl stress, which, in turn, resulted in a better PSII quantum efficiency, better utilization of photochemical energy with significantly reduced energy loss, and higher electron transport rates, even under stressful conditions. The expression of key genes responsible for salt tolerance (NHX1 and AVP1, which are nuclear-encoded) and photosynthesis (psbA, psaA, petB, and rbcL, which are chloroplast-encoded) were monitored for their genetic differences underlying stress tolerance. Under NaCl stress, the expression of NHX1, D1, and Rubisco increased several folds in B. juncea plants compared to B. napus, highlighting differences in genetics between these two Brassicas. The higher photosynthetic potential under stress suggests that B. juncea is a promising candidate for genetic modifications and its cultivation on marginal lands.

Differential tissue-specific accumulation and function of tocochromanols in grape berries

Grape berries have been extensively studied in terms of antioxidant characterization, specifically in anthocyanin, total phenol, and tannin accumulation. However, very little is known about vitamin E composition and contents in this fruit. Aiming to examine the function of vitamin E during grape berries ripening, tocochromanol contents and composition were evaluated in berries and leaves of grapevines (Vitis vinifera L. cv. Merlot), from just before veraison to commercial harvest. We also determined the time-course evolution of tocochromanol accumulation in various fruit tissues, including the skin, pulp, and seeds, and measured the extent of primary and secondary lipid peroxidation, as well as fruit technological maturity parameters. Vitamin E accumulated at higher levels in leaves than in fruits, although the tissue-specific evaluation of tocochromanol contents revealed that berry skin is also rich in α-tocopherol whereas tocotrienols were present in seeds only. α-Tocopherol content decreased during ripening, more specifically in the skin, and it was accompanied by an increase in the extent of lipid peroxidation. Contents and variations in the levels of α-tocopherol, but not those of the other tocochromanols, were inversely related to changes in lipid peroxidation during fruit ripening, as indicated by tissue-specific variations in malondialdehyde contents. In conclusion, α-tocopherol is more abundant in leaves than fruit, yet it apears to exert a role in the modulation of the extent of lipid peroxidation in grape berries, more specifically in the skin, where α-tocopherol depletion and malondialdehyde accumulation may be related to an adequate progression of fruit ripening.

Chronic Ionizing Radiation of Plants: An Evolutionary Factor from Direct Damage to Non-Target Effects

In present times, the levels of ionizing radiation (IR) on the surface of Earth are relatively low, posing no high challenges for the survival of contemporary life forms. IR derives from natural sources and naturally occurring radioactive materials (NORM), the nuclear industry, medical applications, and as a result of radiation disasters or nuclear tests. In the current review, we discuss modern sources of radioactivity, its direct and indirect effects on different plant species, and the scope of the radiation protection of plants. We present an overview of the molecular mechanisms of radiation responses in plants, which leads to a tempting conjecture of the evolutionary role of IR as a limiting factor for land colonization and plant diversification rates. The hypothesis-driven analysis of available plant genomic data suggests an overall DNA repair gene families' depletion in land plants compared to ancestral groups, which overlaps with a decrease in levels of radiation exposure on the surface of Earth millions of years ago. The potential contribution of chronic IR as an evolutionary factor in combination with other environmental factors is discussed.

Tocopherols in Cultivated Apple Malus sp. Seeds: Composition, Variability and Specificity

The seeds of 111 Malus sp. different fruit use (dessert and cider apples) cultivars/genotypes developed in 18 countries were analysed to evaluate composition of tocopherol homologues and identify crop-specific profile, including diploid, triploid, and tetraploid apple cultivars with and without scab-resistance to ensure high genetic diversity. The percentage of individual tocopherols was as follows: alpha-tocopherol (alpha-T) (38.36%), beta-tocopherol (beta-T) (40.74%), gamma-tocopherol (gamma-T) (10.93%), and delta-tocopherol (delta-T) (9.97%), represented by average measurements of 17.48, 18.56, 4.98, and 4.54 mg/100 g dry weight, respectively. The values of the variation coefficient showed high variability for delta (0.695) and gamma (0.662) homologue content, whereas measurements of alpha-T and beta-T were less variable (coefficient of variation 0.203 and 0.256, respectively). The unweighted pair group method with arithmetic mean (UPGMA) revealed three main cultivar groups characterised by almost equal content of all four tocopherol homologues (Group I), high concentrations of alpha-T and beta-T, but very low content of gamma-T and delta-T (Group II), and relatively high average content of alpha-T and beta-T, but higher gamma-T and delta-T content (Group III). Specific tocopherol homologues showed association with certain valuable traits, such as harvesting time (total content of tocopherols) and resistance to apple scab (alpha-T and total content of tocopherols). This study represents the first large-scale tocopherol homologue (alpha, beta, gamma, and delta) screening in apple seeds. The dominant tocopherol homologues in cultivated apple cultivars are alpha-T and beta-T, with the prevalence of alpha-T or beta-T depending on genotype. It is a unique finding due to the rare occurrence of beta-T in the plant world and is considered a unique feature of the species.

Metabolomic Analysis of Key Metabolites and Their Pathways Revealed the Response of Alfalfa (Medicago sativa L.) Root Exudates to rac-GR24 under Drought Stress

The rac-GR24, an artificial analog of strigolactone, is known for its roles in inhibiting branches, and previous studies have reported that it has a certain mechanism to relieve abiotic stress, but the underlying metabolic mechanisms of mitigation for drought-induced remain unclear. Therefore, the objectives of this study were to identify associated metabolic pathways that are regulated by rac-GR24 in alfalfa (Medicago sativa L.) and to determine the metabolic mechanisms of rac-GR24 that are involved in drought-induced root exudate. The alfalfa seedling WL-712 was treated with 5% PEG to simulate drought, and rac-GR24 at a concentration of 0.1 µM was sprayed. After three days of treatment, root secretions within 24 h were collected. Osmotic adjustment substances and antioxidant enzyme activities were measured as physiological indicators, while LS/MS was performed to identify metabolites regulated by rac-GR24 of root exudate under drought. The results demonstrated that rac-GR24 treatment could alleviate the negative effects from drought-induced on alfalfa root, as manifested by increased osmotic adjustment substance content, cell membrane stability, and antioxidant enzyme activities. Among the 14 differential metabolites, five metabolites were uniquely downregulated in plants in rac-GR24 treatment. In addition, rac-GR24 could relieve drought-induced adverse effects on alfalfa through metabolic reprogramming in the pathways of the TCA cycle, pentose phosphate, tyrosine metabolism, and the purine pathway. This study indicated that rac-GR24 could improve the drought resistance of alfalfa by influencing the components of root exudates.

Alpha-Tocopherol from people to plants is an essential cog in the metabolic machinery

SIGNIFICANCE

Protection from oxygen, a di-radical, became a necessity with the evolution of photosynthetic organisms about 2.7 billion years. α-Tocopherol plays an essential role in organisms from plants to people. An overview of human conditions that result in severe vitamin E (α-tocopherol) deficiency is provided.

RECENT ADVANCES

α-Tocopherol has a critical role in the oxygen protection system by stopping lipid peroxidation, its induced damage and cellular death by ferroptosis. Recent findings in bacteria and plants support the concept of why lipid peroxidation is so dangerous to life and why the family of tocochromanols are essential for aerobic organisms and for plants.

CRITICAL ISSUES

The hypothesis that prevention of the propagation of lipid peroxidation is the basis for the α-tocopherol requirement in vertebrates is proposed and further that its absence dysregulates energy metabolism, one-carbon metabolism and thiol homeostasis. By recruiting intermediate metabolites from adjacent pathways to sustain effective lipid hydroperoxide elimination, α-tocopherol function is linked not only to NADPH metabolism and its formation through the pentose phosphate pathway via glucose metabolism, but also to sulfur-containing amino acid metabolism, and to one-carbon metabolism.

FUTURE DIRECTIONS

Evidence from humans, animals and plants support the hypothesis but future studies are needed to assess the genetic sensors that detect lipid peroxidation and cause the ensuing metabolic dysregulation.

Efficacy of Sterculia diversifolia Leaf Extracts: Volatile Compounds, Antioxidant and Anti-Inflammatory Activity, and Green Synthesis of Potential Antibacterial Silver Nanoparticles

Sterculia diversifolia, widely distributed in Jordan as an ornamental plant, is a synonoum for Brachychiton populneus. Phytochemical studies examining the volatile chemicals in Sterculia diversifolia leaves are limited, despite the rising demand for their numerous applications. Furthermore, it was only recently that a report described the friendly synthesis of silver nanoparticles (AgNPs) using aqueous extract derived from Brachychiton populneus leaves. Therefore, AgNPs were produced using either aqueous plant extracts (AgWPE) or ethanolic plant extracts (AgEPE), and Shimadzu GC-MS equipment was used to detect volatile compounds in the ethanolic leaf extracts. GC-MS profile of leaf ethanolic extracts of the Jordanian chemotypes of S. diversifolia revealed the existence of major components: (3β)-Lup-20(29)-en-3-ol acetate (30.97%) and 1-octadecyne (24.88). Other compounds are squalene (7.19%), germanicol (6.23), dl-α-tocopherol (5.24), heptacosane (4.41), phytol (3.54) and pentacosane (2.89). According to published studies, these reported chemicals have numerous uses, including as animal feed, vitamin precursors, possible eco-friendly herbicides, antioxidants, and anti-inflammatory agents. Aqueous extracts of S. diversifolia leaves had total phenolic of 5.33 mg GAE/g extract and flavonoid contents of 64.88 mg QE/g extract, respectively. The results indicated the contribution of phenolic and flavonoids to this plant’s anti-inflammatory and antioxidant properties. The reduction in AgNO₃ to AgNPs using S. diversifolia leaf extracts was confirmed by the change in solution color from colorless to dark black. Further characterization was attempted by X-ray diffraction, Malvern zeta-sizer and scanning electron microscope. The efficacy of synthesized Ag nanoparticles using aqueous or ethanolic plant extract of S. diversifolia against the Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus showed appreciable activity at 25 µg/mL concentration compared to the source plant extracts.

Vitamin E synthesis and response in plants

Vitamin E, also known as tocochromanol, is a lipid-soluble antioxidant that can only be produced by photosynthetic organisms in nature. Vitamin E is not only essential in human diets, but also required for plant environment adaptions. To synthesize vitamin E, specific prenyl groups needs to be incorporated with homogentisate as the first step of reaction. After decades of studies, an almost complete roadmap has been revealed for tocochromanol biosynthesis pathway. However, chlorophyll-derived prenyl precursors for synthesizing tocochromanols are still a mystery. In recent years, by employing forward genetic screening and genome-wide-association approaches, significant achievements were acquired in studying vitamin E. In this review, by summarizing the recent progresses in vitamin E, we provide to date the most updated whole view of vitamin E biosynthesis pathway. Also, we discussed about the role of vitamin E in plants stress response and its potential as signaling molecules.

UV activated sodium percarbonate to accelerate degradation of atrazine: Mechanism, intermediates, and evaluation on residual toxicity by metabolomics

Efficient and safe removal of widely used herbicides such as atrazine has become a recent hotspot. Herein, UV driven sodium percarbonate system (UV/SPC) was established to have many advantages in remediation of atrazine contamination. The mechanism and environmental risk of intermediates were explored, which provided information for the feasibility of UV/SPC. The degradation efficiency of atrazine was significantly enhanced as the increasing dosage of SPC. Quenching assay identified that •OH and CO3•- were committed to degrading atrazine. Humic acid and HPO42- remarkably inhibited atrazine degradation. Several intermediates were generated through the dealkylation, dechlorination-hydroxylation, alkylic-hydroxylation, alkyl oxidation and olefination reactions. Toxicity prediction proved that acute toxicity and bioaccumulation of intermediates were mitigated comparing with atrazine. Based on metabolomics results, the alteration of key metabolites such as citrate, L-kynurenine, malic acid, putrescine, glutamine, spermine, ethanolamine and phytosphingosine in various metabolic pathways of E.coli verified that the toxicity of atrazine was weakened after UV/SPC treatment. The application of UV/SPC on atrazine removal in real waters was influenced by environmental factors, and might be improved through coupling with other treatment technologies.

Nutritional Quality and Oxidative Stability during Thermal Processing of Cold-Pressed Oil Blends with 5:1 Ratio of ω6/ω3 Fatty Acids

The growing awareness of consumers means that new products are sought after, which, apart from meeting the basic demand for macronutrients and energy, will have a positive impact on our health. This article is a report on the characteristics of the new oil blends with a nutritious ω6/ω3 fatty acid ratio (5:1), as well as the heat treatment effect on the nutritional value and stability of the oils. Prepared oil blends were heated at 170 and 200 °C. The fatty acid composition and the changes in tocochromanols content during heating were analyzed, as well as the formation process of polar compounds and triacylglycerol polymers. During heating the highest loss of tocochromanols was characteristic of α-tocopherol and α-tocotrienol. The total content of tocopherols after heating was reduced to 1–6% of the original content in the unheated oil blends. The exception was the blend of oil with wheat germ oil, in which a high content of all tocopherols was observed in unheated and heated samples. The content of the polar fraction during heating increased on average 1.9 and 3.1 times in the samples heated at 170 and 200 °C, respectively, compared to the unheated oils. The level of the polar fraction was related to the high content of tocopherols or the presence of tocopherols and tocotrienols in the heated sample. The polymerization of triacylglycerols led mainly to the formation of triacylglycerol dimers. Trimers were observed in a small number of heated samples, especially those heated at 200 °C. Regardless of the changes in heated oils, none of the prepared blends exceeded the limit of the polar fraction content, maintaining the programmed ratio of ω6 to ω3 acids. The principal component analysis (PCA) used to define the clusters showed a large variety of unheated and heated samples. An outlier in all clusters was a blend of oil with wheat germ oil. In these samples, the degradation of tocopherols molecules and the increase of triacylglycerol polymers and the polar fraction content were the slowest.

Genetic mapping of loci involved in oil tocopherol composition control in Russian sunflower (Helianthus annuus L.) lines

Tocopherols are antioxidants that preserve oil lipids against oxidation and serve as a natural source of vitamin E in the human diet. Compared with other major oilseeds like rapeseed and soybean, sunflower (Helianthus annuus L.) exhibits low phenotypic diversity of tocopherol composition, both in wild and cultivated accessions from germplasm collections. Two major mutations that alter tocopherol composition were identified in genetic collections, and several studies suggested additional loci controlling tocopherol composition, with their expression possibly depending on the genetic background. In the present study, we performed QTL mapping of tocopherol composition in two independent F2 crosses between lines with contrasting tocopherol composition from the Pustovoit All-Russia Research Institute of Oil Crops (VNIIMK) collection. We used genotyping-bysequencing (GBS) to construct single nucleotide polymorphism-based genetic maps, and performed QTL mapping using quantitative and qualitative encoding for phenotypic traits. Our results support the notion that the tocopherol composition in the assessed crosses is controlled by two loci. We additionally selected and validated two single nucleotide polymorphism markers for each cross which could be used for marker-assisted selection.

Amplified Drought and Seasonal Cycle Modulate Quercus pubescens Leaf Metabolome

The intensification of summer drought expected with climate change can induce metabolism modifications in plants to face such constraints. In this experiment, we used both a targeted approach focused on flavonoids, as well as an untargeted approach, to study a broader fraction of the leaf metabolome of Quercus pubescens exposed to amplified drought. A forest site equipped with a rainfall exclusion device allowed reduction of natural rainfall by ~30% over the tree canopy. Leaves of natural drought (ND) and amplified drought (AD) plots were collected over three seasonal cycles (spring, summer, and autumn) in 2013 (the second year of rain exclusion), 2014, and 2015. As expected, Q. pubescens metabolome followed a seasonal course. In the summer of 2015, the leaf metabolome presented a shifted and early autumnal pattern because of harsher conditions during this year. Despite low metabolic modification at the global scale, our results demonstrated that 75% of Quercus metabolites were upregulated in springs when trees were exposed to AD, whereas 60 to 73% of metabolites (93% in summer 2015), such as kaempferols and quercetins, were downregulated in summers/autumns. Juglanin, a kaempferol pentoside, as well as rhododendrin derivatives, were upregulated throughout the year, suggesting an antioxidant ability of these metabolites. Those changes in terms of phenology and leaf chemistry could, in the end, affect the ecosystem functioning.

Inhibition of 4-HYDROXYPHENYLPYRUVATE DIOXYGENASE expression by brassinosteroid reduces carotenoid accumulation in Arabidopsis

Unlike the indispensable function of the steroid hormone brassinosteroid (BR) in regulating plant growth and development, the metabolism of secondary metabolites regulated by BR is not well known. Here we show that BR reduces carotenoid accumulation in Arabidopsis seedlings. BR-deficient or BR-insensitive mutants accumulated higher content of carotenoids than wild-type plants, whereas BR treatment reduced carotenoid content. We demonstrated that BR transcriptionally suppresses 4-HYDROXYPHENYLPYRUVATE DIOXYGENASE (HPPD) expression involved in carotenogenesis via plastoquinone production. We found that the expression of HPPD displays an oscillation pattern that is expressed more strongly in dark than in light conditions. Moreover, BR appeared to inhibit HPPD expression more strongly in darkness than in light, leading to suppression of a diurnal oscillation of HPPD expression. BR-responsive transcription factor BRASSINAZOLE RESISTANT 1 (BZR1) directly bound to the promoter of HPPD, and HPPD suppression by BR was increased in the bzr1-1D gain-of-function mutation. Interestingly, dark-induced HPPD expression did not cause carotenoid accumulation, due to down-regulation of other carotenoid biosynthetic genes in the dark. Our results suggest that BR regulates different physiological responses in dark and light through inhibition of HPPD expression.

Chemical role of α-tocopherol in salt stress mitigation by improvement in morpho-physiological attributes of sunflower (Helianthus annuus L.)

Elevated concentrations of salts in soil and water represent abiotic stresses. It considerably restricts plant productivity. However, the use of alpha-tocopherol (α-toc) as foliar can overcome this problem. It can improve crop productivity grown under salinity stress. Limited literature is documented regarding its optimum foliar application on sunflower. That’s why the need for the time is to optimize α-toc foliar application rates for sunflower cultivated in salt-affected soil. A pot experiment was performed to select a better α-toc foliar application for mitigation of salt stress in different sunflower cultivars FH (572 and 621). There were 2 levels of salts, i.e., control (no salt stress) and sodium chloride (120 mM) and four α-toc foliar application (0, 100, 200, and 300 mg L⁻¹). Results showed that foliar application of 100 mg/L- α-toc triggered the remarkable increase in fresh shoot weight, fresh root weight, shoot, and root lengths under salinity stress in FH-572 and FH-621 over 0 mg/L- α-toc. Foliar application of 200 mg/L- α-toc was most effective for improvement in chlorophyll a, chlorophyll b, total chlorophyll and carotenoids compared to 0 mg/L- α-toc. Furthermore, an increase in A was noted in FH-572 (17%) and FH-621 (22%) with α-toc (300 mg L⁻¹) application under saline condition. In conclusion, the 100 and 200 mg/L- α-toc are the best application rates for the improvement in sunflower FH-572 and FH-621 growth, chlorophyll contents and gas exchange attributes. Further investigations are needed to select a better foliar application rate between 100 and 200 mg/L- α-toc at the field level under the different agro-climatic zone and soil types.

Vitamin E protects from lipid peroxidation during winter stress in the seagrass Cymodocea nodosa

Adjustments in the antenna size and α-tocopherol contents provide protection from sustained damage in leaves of a seagrass, while low vitamin E contents appear to be enough to protect rhizomes (which appear to be more cold tolerant than leaves). Despite low temperatures can adversely affect the proper growth and development of marine angiosperms, by, among other processes, increasing reactive oxygen species production and causing oxidative damage to lipid membranes, the role of vitamin E in seagrasses, such as Cymodocea nodosa has not been explored thus far. Here, we aimed to better understand the possible role of this chain-breaking (peroxyl radical-trapping) antioxidant in response to low temperatures, and most particularly in relation to the occurrence of photo-inhibition and lipid peroxidation. Low temperatures caused an important desiccation of leaves, but not of rhizomes, which were much more tolerant to cold stress than leaves. Cold stress during winter was associated with chlorophyll loss and transient photo-inhibition, as indicated by reversible reductions in the F_v/F_m ratio. Adjustments in pigment antenna size and vitamin E contents per unit of chlorophyll during winter may help protect the photosynthetic apparatus from sustained photo-inhibitory damage and lipid peroxidation events in leaves. Rhizomes also accumulated significant amounts of vitamin E, although to a much lesser extent than leaves, and kept protected from lipid peroxidation during winter, as indicated by malondialdehyde contents, a product from secondary lipid peroxidation. It is concluded that vitamin E can help protect both leaves and rhizomes from lipid peroxidation, although cold stress during winter can cause transient photo-inhibition of the photosynthetic apparatus, in C. nodosa.

Differential physiological response to heat and cold stress of tomato plants and its implication on fruit quality

The upcoming climate change presents a great challenge for plant growth and development being extremes temperatures among the major environmental limitations to crop productivity. Understanding the repercussions of these extreme temperatures is of high importance to elaborate future strategies to confront crop damages. Tomato plants (Solanum lycopersicum L.) are one of the most cultivated crops and their fruits are consumed worldwide standing out for their organoleptic characteristics and nutritional value. Tomato plants are sensitive to temperatures below 12 °C and above 32 °C. In this study, Micro-Tom cultivar was used to evaluate the effects of extreme temperatures on the plant of tomato and the fruit productivity and quality from the stressed plants, either exposed to cold (4 °C for three nights per week) or heat (32 °C during the day, seven days per week) treatments. Total productivity and the percentage of ripe fruits per plant were evaluated together with foliar stress markers and the contents of photosynthetic pigments and tocochromanols. Fruit quality was also assessed determining lycopene contents, total soluble solids, total acidity and ascorbate contents. High temperatures altered multiple physiological parameters indicating a moderate stress, particularly decreasing fruit yield. As a response to this stress, plants enhanced their antioxidant contents both at leaf and fruit level. Low temperatures did not negatively affect the physiology of plants with similar yields as compared to controls, suggesting chilling acclimation. Both high and low temperatures, but most particularly the former, increased total soluble solids contents indicating that temperature control may be used as a strategy to modulate fruit quality.

Effect of fruit shading and cold storage on tocopherol biosynthesis and its involvement in the susceptibility of Star Ruby grapefruit to chilling injury

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Tocopherol content in the flavedo of grapefruit increase during fruit maturation.

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TAT1 and genes of the tocopherol-core pathway are up-regulated during fruit maturation.

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Light avoidance reduces γ-tocopherol and expression of GGDR and tocopherol-core pathway genes.

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Cold up-regulated genes involved in precursors supply but repressed those of the core pathway.

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Changes in tocopherols during storage appears to be cold-mediated and not related to CI tolerance.

The aim of this study was to investigate the role of tocopherols in the susceptibility of Star Ruby grapefruit to postharvest chilling injury (CI). Fruit exposed to normal sunlight (NC, non-covered) and deprived of light (C, covered) in the last stages of development were used. Tocopherol contents increased in the flavedo of both NC and C fruit during development, concomitantly with the up-regulation of TAT1 and most genes of the tocopherol-core pathway. Fruit shading reduced total contents by repressing γ-tocopherol accumulation, associated to a down-regulation of GGDR and VTE1 and, to a lesser extent, of VTE2, VTE3a and VTE4. During cold storage, total and α-tocopherol contents increased in NC and C fruit, and no direct relationship between tocopherol accumulation and CI tolerance was found. Cold stress up-regulated most genes involved in the synthesis of tocopherol precursors and down-regulated those of the tocopherol-core pathway, but changes seemed to be cold-mediated and not related to CI development.

Chemistry and Functionality of Cold-Pressed Macadamia Nut Oil

The rising trend in the consumption of healthy, safe, and functional foods has motivated studies on cold-pressed specialty oils, including macadamia nut oil. Cold-pressed macadamia nut oil (CPMO) is given preference by consumers over solvent extracted and refined oil because of its exceptional quality attributes and safety. This review contains a detailed presentation of the chemical properties, health benefits, and applications of CPMO. The monounsaturated fatty acids (oleic acid and palmitoleic acid) rich oil also contains a significant concentration of bioactive phytochemicals including, β-sitosterol, α-tocopherol, α-tocotrienols, ρ-hydroxybenzoic acid, and caffeic acid. Moreover, the oil has good oxidative stability. The highlighted properties offer CPMO health benefits related to the prevention of cardiovascular diseases, diabetes, cancer, high blood pressure, and neurodegenerative diseases. The fatty acid composition of CPMO allows for its diverse application in the food, cosmetic, nutraceutical, and pharmaceutical industries.

The halophyte gene ScVTC2 confers resistance to oxidative stress via AsA-mediated photosynthetic enhancement

Various abiotic stresses commonly cause excessive production of reactive oxygen species (ROS) and result in oxidative stress, which challenges the physiological homeostasis of plants. Maintaining a delicate balance between ROS generation and removal is critical for plants to cope with stressful environments. Suaeda corniculata is a typical euhalophyte with strong tolerance to salt stress, but its mechanism of ROS detoxification to prevent oxidative stress is unknown. Here, a combined analysis of RNA-Seq and photosynthetic assays was performed on S. corniculata under oxidative stress to uncover the underlying mechanism that modulates oxidative tolerance. Our results showed that all genes involved in the pathway of ROS scavenging, especially the AsA-GSH pathway, were highly enriched under oxidative stress. Notably, VTC2 (GGPase), which functions in the L-galactose pathway of AsA synthesis, was significantly upregulated. Arabidopsis transgenic plants with heterologous expression of ScVTC2 showed elevated AsA and increased tolerance to oxidative stress. Furthermore, ScVTC2 also established better photosynthetic capacity in these plants upon oxidative treatment. Thus, ScVTC2 not only functioned as an effective ROS scavenger but also as a protector of the photosynthetic apparatus in S. corniculata and allowed plants to respond to and tolerate oxidative stress.

Development of Analytical Strategies for the Determination of Olive Fruit Bioactive Compounds Using UPLC-HRMS and HPLC-DAD. Chemical Characterization of Kolovi Lesvos Variety as a Case Study

In this study, an overall survey regarding the determination of several bioactive compounds in olive fruit is presented. Two methodologies were developed, one UPLC-Q-TOF-MS method for the determination of olive fruit phenolic compounds and one HPLC-DAD methodology targeting the determination of pigments (chlorophylls and carotenoids), tocopherols (α-, β, -γ, δ-) and squalene. Target and suspect screening workflows were developed for the thorough fingerprinting of the phenolic fraction of olives. Both methods were validated, presenting excellent performance characteristics, and can be used as reliable tools for the monitoring of bioactive compounds in olive fruit samples. The developed methodologies were utilized to chemical characterize the fruits of the Kolovi olive variety, originating from the island of Lesvos, North Aegean Region, Greece. Twenty-five phenolic compounds were identified and quantified in Kolovi olives with verbascoside, hydroxytyrosol, oleacein and oleomissional found in significantly high concentrations. Moreover, 12 new bioactive compounds were identified in the samples using an in-house suspect database. The results of pigments analysis suggested that Kolovi variety should be characterized as low pigmentation, while the tocopherol and squalene content was relatively high compared to other olive varieties. The characterization of Kolovi olive bioactive content highlighted the high nutritional and possible economic value of the Kolovi olive fruit.

Metabolomic Variability of Different Soybean Genotypes: β-Carotene-Enhanced (Glycine max), Wild (Glycine soja), and Hybrid (Glycine max × Glycine soja) Soybeans

We obtained a new hybrid soybean (Hybrid) by hybridizing β-carotene-enhanced soybean (BCE; Glycine max L.) containing the phytoene synthase-2A-carotene desaturase gene and wild-type soybean (Wild; Glycine soja). To investigate metabolic changes between variants, we performed metabolic profiling of leaves (three growth stages) and seeds. Multivariate analyses revealed significant metabolic differences between genotypes in seeds and leaves, with seeds showing accumulation of phytosterols, tocopherols, and carotenoids (BCE only), indicating co-induction of the methylerythritol 4-phosphate and mevalonic acid pathways. Additionally, Hybrid produced intermediate levels of carotenoids and high levels of amino acids. Principal component analysis revealed metabolic discrimination between growth stages of soybean leaves and identified differences in leaf groups according to different genotypes at 8, 12, and 16 weeks, with Wild showing higher levels of environmental stress-related compounds relative to BCE and Hybrid leaves. The metabolic profiling approach could be a useful tool to identify metabolic links in various soybean cultivars.

Regulation of Tocopherol Biosynthesis During Fruit Maturation of Different Citrus Species

Tocopherols are plant-derived isoprenoids with vitamin E activity, which are involved in diverse physiological processes in plants. Although their biosynthesis has been extensively investigated in model plants, their synthesis in important fruit crops as Citrus has scarcely been studied. Therefore, the aim of this work was to initiate a physiological and molecular characterization of tocopherol synthesis and accumulation in Citrus fruits during maturation. For that purpose, we selected fruit of the four main commercial species: grapefruit (Citrus paradisi), lemon (Citrus limon), sweet orange (Citrus sinensis), and mandarin (Citrus clementina), and analyzed tocopherol content and the expression profile of 14 genes involved in tocopherol synthesis during fruit maturation in both the flavedo and pulp. The selected genes covered the pathways supplying the tocopherol precursors homogentisate (HGA) (TAT1 and HPPD) and phytyl pyrophosphate (PPP) (VTE5, VTE6, DXS1 and 2, GGPPS1 and 6, and GGDR) and the tocopherol-core pathway (VTE2, VTE3a, VTE3b, VTE1, and VTE4). Tocopherols accumulated mainly as α- and γ-tocopherol, and α-tocopherol was the predominant form in both tissues. Moreover, differences were detected between tissues, among maturation stages and genotypes. Contents were higher in the flavedo than in the pulp during maturation, and while they increased in the flavedo they decreased or were maintained in the pulp. Among genotypes, mature fruit of lemon accumulated the highest tocopherol content in both the flavedo and the pulp, whereas mandarin fruit accumulated the lowest concentrations, and grapefruit and orange had intermediate levels. Higher concentrations in the flavedo were associated with a higher expression of all the genes evaluated, and different genes are suitable candidates to explain the temporal changes in each tissue: (1) in the flavedo, the increase in tocopherols was concomitant with the up-regulation of TAT1 and VTE4, involved in the supply of HGA and the shift of γ- into α-tocopherol, respectively; and (2) in the pulp, changes paralleled the expression of VTE6, DXS2, and GGDR, which regulate PPP availability. Also, certain genes (i.e., VTE6, DXS2, and GGDR) were co-regulated and shared a similar pattern during maturation in both tissues, suggesting they are developmentally modulated.

Multi-omics analyses on the response mechanisms of 'Shine Muscat' grapevine to low degree of excess copper stress (Low-ECS)

Copper stress is one of the most severe heavy metal stresses in plants. Grapevine has a relatively higher copper tolerance than other fruit crops. However, there are no reports regarding the tolerance mechanisms of the 'Shine Muscat' ('SM') grape to a low degree of excess copper stress (Low-ECS). Based on the physiological indicators and multi-omics (transcriptome, proteome, metabolome, and microRNAome) data, 8 h (h) after copper treatment was the most severe stress time point. Nonetheless, copper stress was alleviated 64 h after treatment. Cu ion transportation, photosynthesis pathway, antioxidant system, hormone metabolism, and autophagy were the primary response systems in 'SM' grapevine under Low-ECS. Numerous genes and proteins, such as HMA5, ABC transporters, PMM, GME, DHAR, MDHAR, ARGs, and ARPs, played essential roles in the 'SM' grapevine's response to Low-ECS. This work was carried out to gain insights into the multi-omics responses of 'SM' grapevine to Low-ECS. This study provides genetic and agronomic information that will guide better vinery management and breeding copper-resistant grape cultivars.

Correlation between leaf epicuticular wax composition and structure, physio-biochemical traits and drought resistance in glaucous and non-glaucous near-isogenic lines of rye

The objective of this research was to investigate the differences between glaucous and non-glaucous near-isogenic lines (NILs) of winter rye (Secale cereale L.) in terms of epicuticular wax layer properties (weight, composition, and crystal morphology), selected physiological and biochemical responses, yield components, above-ground biomass, and plant height under soil drought stress. An important aspect of this analysis was to examine the correlation between the above characteristics. Two different NIL pairs were tested, each consisting of a typical glaucous line and a non-glaucous line with a recessive mutation. The drought experiment was conducted twice (2015-2016). Our study showed that wax accumulation during drought was not correlated with higher leaf hydration and glaucousness. Environmental factors had a large impact on the response of the lines to drought in individual years, both in terms of physiological and biochemical reactions, and the composition of epicuticular leaf wax. The analysed pairs displayed significantly different responses to drought. Demonstration of the correlation between the components of rye leaf wax and the physiological and biochemical parameters of rye NILs is a significant achievement of this work. Interestingly, the study showed a correlation between the wax components and the content of photosynthetic pigments and tocopherols, whose biosynthesis, similarly to the biosynthesis of wax precursors, is mainly located in chloroplasts. This suggests a relationship between wax biosynthesis and plant response to various environmental conditions and drought stress.

Pressurized liquid extraction to obtain chia seeds oils extracts enriched in tocochromanols. Nanoemulsions approaches to preserve the antioxidant potential

The objective of this study was to use accelerated-solvent-extraction to achieve antioxidant extracts from chia seeds oils, enriched in tocopherols and tocotrienols, namely tocochromanols. Nanotechnology applications have been also incorporated to develop an innovative formulation of chia seeds oil nanoemulsion that preserve its antioxidant potential after conditions of oxidative stress. Chia seeds oils proved to be a valuable source of tocochromanols, from 568.84 to 855.98 μg g^-1, depending on the geographical provenance. Quantitative data obtained by LC-DAD-ESI-MS/MS showed outstanding levels of γ-Tocopherol, over 83%, followed far behind by Tocopherols-(α, β, δ) and Tocotrienols-(α, β, δ, γ)-tocotrienols. The characteristic tocochromanols fingerprint of chia seeds oils was positively correlated with the FRAP and DPPH antioxidant activity of the extracts (between 18.81 and 138.48 mg Trolox/g). Formulation of the Chia seeds oils as nanoemulsions did not compromised the antioxidant properties of fresh extracts. Interestingly, nanoemulsions retained about the 80% of the initial antioxidant capacity after UV-induced stress, where the non-emulsified oils displayed a remarkable reduction (50-60%) on its antioxidant capacity under the same conditions. These antioxidant chia seeds formulations can constitute a promising strategy to vectorizing vitamin E isomers, in order to be used for food fortification, natural additives and to increase the self-life of food products during packing.

Tocopherol controls D1 amino acid oxidation by oxygen radicals in Photosystem II

Photosystem II (PSII) is an intrinsic membrane protein complex that functions as a light-driven water:plastoquinone oxidoreductase in oxygenic photosynthesis. Electron transport in PSII is associated with formation of reactive oxygen species (ROS) responsible for oxidative modifications of PSII proteins. In this study, oxidative modifications of the D1 and D2 proteins by the superoxide anion (O₂ ^•-) and the hydroxyl (HO^•) radicals were studied in WT and a tocopherol cyclase (vte1) mutant, which is deficient in the lipid-soluble antioxidant α-tocopherol. In the absence of this antioxidant, high-resolution tandem mass spectrometry was used to identify oxidation of D1:¹³⁰E to hydroxyglutamic acid by O₂ ^•- at the Pheo_D1 site. Additionally, D1:²⁴⁶Y was modified to either tyrosine hydroperoxide or dihydroxyphenylalanine by O₂ ^•- and HO^•, respectively, in the vicinity of the nonheme iron. We propose that α-tocopherol is localized near Pheo_D1 and the nonheme iron, with its chromanol head exposed to the lipid-water interface. This helps to prevent oxidative modification of the amino acid's hydrogen that is bonded to Pheo_D1 and the nonheme iron (via bicarbonate), and thus protects electron transport in PSII from ROS damage.

Production of tocotrienols in seeds of cotton (Gossypium hirsutum L.) enhances oxidative stability and offers nutraceutical potential

Upland cotton (Gossypium hirsutum L.) is an economically important multi-purpose crop cultivated globally for fibre, seed oil and protein. Cottonseed oil also is naturally rich in vitamin E components (collectively known as tocochromanols), with α- and γ-tocopherols comprising nearly all of the vitamin E components. By contrast, cottonseeds have little or no tocotrienols, tocochromanols with a wide range of health benefits. Here, we generated transgenic cotton lines expressing the barley (Hordeum vulgare) homogentisate geranylgeranyl transferase coding sequence under the control of the Brassica napus seed-specific promoter, napin. Transgenic cottonseeds had ~twofold to threefold increases in the accumulation of total vitamin E (tocopherols + tocotrienols), with more than 60% γ-tocotrienol. Matrix assisted laser desorption ionization-mass spectrometry imaging showed that γ-tocotrienol was localized throughout the transgenic embryos. In contrast, the native tocopherols were distributed unequally in both transgenic and non-transgenic embryos. α- Tocopherol was restricted mostly to cotyledon tissues and γ-tocopherol was more enriched in the embryonic axis tissues. Production of tocotrienols in cotton embryos had no negative impact on plant performance or yield of other important seed constituents including fibre, oil and protein. Advanced generations of two transgenic events were field grown, and extracts of transgenic seeds showed increased antioxidant activity relative to extracts from non-transgenic seeds. Furthermore, refined cottonseed oil from the two transgenic events showed 30% improvement in oxidative stability relative to the non-transgenic cottonseed oil. Taken together, these materials may provide new opportunities for cottonseed co-products with enhanced vitamin E profile for improved shelf life and nutrition.

Different tolerance to salinity of two populations of Oenothera drummondii with contrasted biogeographical origin

Oenothera drummondii is a native species from the coastal dunes of the Gulf of Mexico that has nowadays extended to coastal areas in temperate zones all over the world, its invasion becoming a significant problem locally. The species grows on back beach and incipient dunes, where it can suffer flooding by seawater, and sea spray. We were interested in knowing how salinity affects this species and if invasive populations present morphological or functional traits that would provide greater tolerance to salinity than native ones. To this end, we conducted a greenhouse experiment where plants from one native and from one invading population were irrigated with five salinity treatments. We measured functional traits on photosynthetic, photochemical efficiency, water content, flowering, Na⁺ content, pigment content, and biomass. Although O. drummondii showed high resistance to salinity, the highest levels recorded high mortality, especially in the invasive population. Plants exhibited differences not only in response to time under salinity conditions, but also according to their biogeographic origin, the native population being more resistant to long exposure and high salt concentration than the invasive one. Native and invasive populations showed different response to salt stress in photosynthesis and transpiration rates, stomatal conductance, water use efficiency, carboxylation efficiency, electron transport rate, electron transport efficiency, energy used in photochemistry, among others. The increasing salinity levels resulted in a progressive reduction of photosynthesis rate due to both stomatal and biochemical limitations, and also in a reduction of biomass and number and size of flowers, compromising the reproductive capacity.

Stem girdling affects the onset of autumn senescence in aspen in interaction with metabolic signals

Autumn senescence in aspen (Populus tremula) is precisely timed every year to relocate nutrients from leaves to storage organs before winter. Here we demonstrate how stem girdling, which leads to the accumulation of photosynthates in the crown, influences senescence. Girdling resulted in an early onset of senescence, but the chlorophyll degradation was slower and nitrogen more efficiently resorbed than during normal autumn senescence. Girdled stems accumulated or retained anthocyanins potentially providing photoprotection in senescing leaves. Girdling of one stem in a clonal stand sharing the same root stock did not affect senescence in the others, showing that the stems were autonomous in this respect. One girdled stem with unusually high chlorophyll and nitrogen contents maintained low carbon-to-nitrogen (C/N) ratio and did not show early senescence or depleted chlorophyll level unlike the other girdled stems suggesting that the responses depended on the genotype or its carbon and nitrogen status. Metabolite analysis highlighted that the tricarboxylic acid (TCA) cycle, salicylic acid pathway, and redox homeostasis are involved in the regulation of girdling-induced senescence. We propose that disrupted sink-source relation and C/N status can provide cues through the TCA cycle and phytohormone signaling to override the phenological control of autumn senescence in the girdled stems.

Antioxidant and Signaling Role of Plastid-Derived Isoprenoid Quinones and Chromanols

Plant prenyllipids, especially isoprenoid chromanols and quinols, are very efficient low-molecular-weight lipophilic antioxidants, protecting membranes and storage lipids from reactive oxygen species (ROS). ROS are byproducts of aerobic metabolism that can damage cell components, they are also known to play a role in signaling. Plants are particularly prone to oxidative damage because oxygenic photosynthesis results in O2 formation in their green tissues. In addition, the photosynthetic electron transfer chain is an important source of ROS. Therefore, chloroplasts are the main site of ROS generation in plant cells during the light reactions of photosynthesis, and plastidic antioxidants are crucial to prevent oxidative stress, which occurs when plants are exposed to various types of stress factors, both biotic and abiotic. The increase in antioxidant content during stress acclimation is a common phenomenon. In the present review, we describe the mechanisms of ROS (singlet oxygen, superoxide, hydrogen peroxide and hydroxyl radical) production in chloroplasts in general and during exposure to abiotic stress factors, such as high light, low temperature, drought and salinity. We highlight the dual role of their presence: negative (i.e., lipid peroxidation, pigment and protein oxidation) and positive (i.e., contribution in redox-based physiological processes). Then we provide a summary of current knowledge concerning plastidic prenyllipid antioxidants belonging to isoprenoid chromanols and quinols, as well as their structure, occurrence, biosynthesis and function both in ROS detoxification and signaling.

Induction of tocopherol biosynthesis through heat shock treatment in Arabidopsis

Plants have developed various self-defense systems to survive many types of unfavorable conditions. Heat shock (HS) treatment, an abiotic stress, activates salicylic acid (SA) biosynthesis to enhance resistance to biotic stresses in some plant species. Since SA is produced from the shikimate pathway, other related metabolic pathways were expected to be upregulated by HS treatment. We speculated that tocopherol biosynthesis utilizing chorismic acid would be activated by HS treatment. In Arabidopsis, expression analysis of tocopherol biosynthetic genes, HPPD, VTE2, VTE3, VTE1, and VTE4, in combination with measurement of metabolites, indicated that HS treatment enhanced the biosynthesis and accumulation of tocopherols. Analyses using an SA biosynthesis-deficient mutant indicated that the upregulation of tocopherol biosynthesis was independent of the SA-mediated signaling pathway.

Aging, stress, and senescence in plants: what can biological diversity teach us?

Aging, stress, and senescence in plants are interconnected processes that determine longevity. We focus here on compiling and discussing our current knowledge on the mechanisms of development that long-lived perennial plants have evolved to prevent and delay senescence. Clonal and nonclonal perennial herbs of various life forms and longevities will be particularly considered to illustrate what biological diversity can teach us about aging as a universal phenomenon. Source-sink relations and redox signaling will also be discussed as examples of regulatory mechanisms of senescence at the organ level. Whether or not effective mechanisms that biological diversity has evolved to completely prevent the wear and tear of aging will be applicable to human aging in the near future ultimately depends on ethical aspects.

Age-dependent increase in α-tocopherol and phytosterols in maize leaves exposed to elevated ozone pollution

Tropospheric ozone is a major air pollutant that significantly damages crop production. Crop metabolic responses to rising chronic ozone stress have not been well studied in the field, especially in C4 crops. In this study, we investigated the metabolomic profile of leaves from two diverse maize (Zea mays) inbred lines and the hybrid cross during exposure to season-long elevated ozone (~100 nl L-1) in the field using free air concentration enrichment (FACE) to identify key biochemical responses of maize to elevated ozone. Senescence, measured by loss of chlorophyll content, was accelerated in the hybrid line, B73 × Mo17, but not in either inbred line (B73 or Mo17). Untargeted metabolomic profiling further revealed that inbred and hybrid lines of maize differed in metabolic responses to ozone. A significant difference in the metabolite profile of hybrid leaves exposed to elevated ozone occurred as leaves aged, but no age-dependent difference in leaf metabolite profiles between ozone conditions was measured in the inbred lines. Phytosterols and α-tocopherol levels increased in B73 × Mo17 leaves as they aged, and to a significantly greater degree in elevated ozone stress. These metabolites are involved in membrane stabilization and chloroplast reactive oxygen species (ROS) quenching. The hybrid line also showed significant yield loss at elevated ozone, which the inbred lines did not. This suggests that the hybrid maize line was more sensitive to ozone exposure than the inbred lines, and up-regulated metabolic pathways to stabilize membranes and quench ROS in response to chronic ozone stress.

Mechanisms Regulating the Dynamics of Photosynthesis Under Abiotic Stresses

Photosynthesis sustains plant life on earth and is indispensable for plant growth and development. Factors such as unfavorable environmental conditions, stress regulatory networks, and plant biochemical processes limits the photosynthetic efficiency of plants and thereby threaten food security worldwide. Although numerous physiological approaches have been used to assess the performance of key photosynthetic components and their stress responses, though, these approaches are not extensive enough and do not favor strategic improvement of photosynthesis under abiotic stresses. The decline in photosynthetic capacity of plants due to these stresses is directly associated with reduction in yield. Therefore, a detailed information of the plant responses and better understanding of the photosynthetic machinery could help in developing new crop plants with higher yield even under stressed environments. Interestingly, cracking of signaling and metabolic pathways, identification of some key regulatory elements, characterization of potential genes, and phytohormone responses to abiotic factors have advanced our knowledge related to photosynthesis. However, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. Here, we provide a detailed overview of the research conducted on photosynthesis to date, and highlight the abiotic stress factors (heat, salinity, drought, high light, and heavy metal) that limit the performance of the photosynthetic machinery. Further, we reviewed the role of transcription factor genes and various enzymes involved in the process of photosynthesis under abiotic stresses. Finally, we discussed the recent progress in the field of biodegradable compounds, such as chitosan and humic acid, and the effect of melatonin (bio-stimulant) on photosynthetic activity. Based on our gathered researched data set, the logical concept of photosynthetic regulation under abiotic stresses along with improvement strategies will expand and surely accelerate the development of stress tolerance mechanisms, wider adaptability, higher survival rate, and yield potential of plant species.

Linking jasmonates with vitamin E accumulation in plants: a case study in the Mediterranean shrub Cistus albidus L

Jasmonic acid positively modulates vitamin E accumulation, but the latter can also partly influence the capacity to accumulate the jasmonic acid precursor, 12-oxo-phytodienoic acid, in white-leaved rockrose (Cistus albidus L.) plants growing in their natural habitat. This study suggests a bidirectional link between chloroplastic antioxidants and lipid peroxidation-derived hormones in plants. While vitamin E is well known for its antioxidant properties being involved in plant responses to abiotic stress, jasmonates are generally related to biotic stress responses in plants. Studying them in non-model plants under natural conditions is crucial for the knowledge on their relationship, which will help us to better understand mechanisms and limits of stress tolerance to implement better conservation strategies in vulnerable ecosystems. We studied a typical Mediterranean shrub, white-leaved rockrose (Cistus albidus) under natural conditions during three winters and we analyzed both α and γ-tocopherol, and the three main jasmonates forms 12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and jasmonoyl-isoleucine (JA-Ile). We found that JA contents positively correlated with vitamin E accumulation, most particularly with γ-tocopherol, the precursor of α-tocopherol (the most active vitamin E form). This finding was confirmed by exogenous application of methyl jasmonate (MeJA) in leaf discs under controlled conditions, which increased γ-tocopherol when applied at 0.1 mM MeJA and α-tocopherol at 1 mM MeJA. Furthermore, a complementary meta-analysis study with previously published reports revealed a positive correlation between JA and vitamin E, although this relationship turned to be strongly species specific. A strong negative correlation was observed, however, between total tocopherols and OPDA (a JA precursor located in chloroplasts). This antagonistic effect was observed between α-tocopherol and OPDA, but not between γ-tocopherol and OPDA. It is concluded that (i) variations in jasmonates and vitamin E due to yearly, inter-individual and sun orientation-driven variability are compatible with a partial regulation of vitamin E accumulation by jasmonates, (ii) vitamin E may also exert a role in the modulation of the biosynthesis of OPDA, with a much smaller effect, if any, on other jasmonates, and (iii) a trade-off in the accumulation of vitamin E and jasmonates might occur in the regulation of biotic and abiotic stress responses in plants.

Interplay between antioxidants in response to photooxidative stress in Arabidopsis

Tocochromanols (tocopherols, tocotrienols and plastochromanol-8), isoprenoid quinone (plastoquinone-9 and plastoquinol-9) and carotenoids (carotenes and xanthophylls), are lipid-soluble antioxidants in the chloroplasts, which play an important defensive role against photooxidative stress in plants. In this study, the interplay between the antioxidant activities of those compounds in excess light stress was analyzed in wild-type (WT) Arabidopsis thaliana and in a tocopherol cyclase mutant (vte1), a homogentisate phytyl transferase mutant (vte2) and a tocopherol cyclase overexpressor (VTE1oex). The results reveal a strategy of cooperation and replacement between α-tocopherol, plastochromanol-8, plastoquinone-9/plastoquinol-9 and zeaxanthin. In the first line of defense (non-radical mechanism), singlet oxygen is either physically or chemically quenched by α-tocopherol; however, when α-tocopherol is consumed, zeaxanthin and plastoquinone-9/plastoquinol-9 can provide alternative protection against singlet oxygen toxicity by functional replacement of α-tocopherol either by zeaxanthin for the physical quenching or by plastoquinone-9/plastoquinol-9 for the chemical quenching. When singlet oxygen escapes this first line of defense, it oxidizes lipids and forms lipid hydroperoxides, which are oxidized to lipid peroxyl radicals by ferric iron. In the second line of defense (radical mechanism), lipid peroxyl radicals are scavenged by α-tocopherol. After its consumption, plastochromanol-8 overtakes this function. We provide a comprehensive description of the reaction pathways underlying the non-radical and radical antioxidant activities of α-tocopherol, carotenoids, plastoquinone-9/plastoquinol-9 and plastochromanol-8. The interplay between the different plastid lipid-soluble antioxidants in the non-radical and the radical mechanism provides step by step insights into protection against photooxidative stress in higher plants.

Formation of α-tocopherol hydroperoxide and α-tocopheroxyl radical: relevance for photooxidative stress in Arabidopsis

Tocopherols, lipid-soluble antioxidants play a crucial role in the antioxidant defense system in higher plants. The antioxidant function of α-tocopherol has been widely studied; however, experimental data on the formation of its oxidation products is missing. In this study, we attempt to provide spectroscopic evidence on the detection of oxidation products of α-tocopherol formed by its interaction with singlet oxygen and lipid peroxyl radical. Singlet oxygen was formed using photosensitizer rose bengal and thylakoid membranes isolated from Arabidopsis thaliana. Singlet oxygen reacts with polyunsaturated fatty acid forming lipid hydroperoxide which is oxidized by ferric iron to lipid peroxyl radical. The addition of singlet oxygen to double bond carbon on the chromanol head of α-tocopherol forms α-tocopherol hydroperoxide detected using fluorescent probe swallow-tailed perylene derivative. The decomposition of α-tocopherol hydroperoxide forms α-tocopherol quinone. The hydrogen abstraction from α-tocopherol by lipid peroxyl radical forms α-tocopheroxyl radical detected by electron paramagnetic resonance. Quantification of lipid and protein hydroperoxide from the wild type and tocopherol deficient (vte1) mutant Arabidopsis leaves using a colorimetric ferrous oxidation-xylenol orange assay reveals that α-tocopherol prevents formation of both lipid and protein hydroperoxides at high light. Identification of oxidation products of α-tocopherol might contribute to a better understanding of the protective role of α-tocopherol in the prevention of oxidative damage in higher plants at high light.

Functional dissection of HGGT and HPT in barley vitamin E biosynthesis via CRISPR/Cas9-enabled genome editing

BACKGROUND AND AIMS

Vitamin E (tocochromanol) is a lipid-soluble antioxidant and an essential nutrient for human health. Among cereal crops, barley (Hordeum vulgare) contains a high level of vitamin E, which includes both tocopherols and tocotrienols. Although the vitamin E biosynthetic pathway has been characterized in dicots, such as Arabidopsis, which only accumulate tocopherols, knowledge regarding vitamin E biosynthesis in monocots is limited because of the lack of functional mutants. This study aimed to obtain gene knockout mutants to elucidate the genetic control of vitamin E composition in barley.

METHODS

Targeted knockout mutations of HvHPT and HvHGGT in barley were created with CRISPR/Cas9-enabled genome editing. High-performance liquid chromatography (HPLC) was performed to analyse the content of tocochromanol isomers in transgene-free homozygous Hvhpt and Hvhggt mutants.

KEY RESULTS

Mutagenesis efficiency among T0 regenerated plantlets was 50-65 % as a result of two simultaneously expressed guide RNAs targeting each gene; most of the mutations were stably inherited by the next generation. The transgene-free homozygous mutants of Hvhpt and Hvhggt exhibited decreased grain size and weight, and the HvHGGT mutation led to a shrunken phenotype and significantly lower total starch content in grains. HPLC analysis revealed that targeted mutation of HvHPT significantly reduced the content of both tocopherols and tocotrienols, whereas mutations in HvHGGT completely blocked tocotrienol biosynthesis in barley grains. Transient overexpression of an HvHPT homologue in tobacco leaves significantly increased the production of γ- and δ-tocopherols, which may partly explain why targeted mutation of HvHPT in barley grains did not eliminate tocopherol production.

CONCLUSIONS

Our results functionally validated that HvHGGT is the only committed gene for the production of tocotrienols, whereas HvHPT is partly responsible for tocopherol biosynthesis in barley.

Differential accumulation of tocochromanols in photosynthetic and non-photosynthetic tissues of strawberry plants subjected to reiterated water deficit

Tocochromanols are a group of lipid-soluble antioxidants that include tocopherols, tocotrienols and plastochromanol-8. Here, we examined a putative differential accumulation of tocochromanols in photosynthetic and non-photosynthetic tissues (including leaves and whole fruits) of strawberry (Fragaria x ananassa cv. Albion) plants and evaluated their endogenous variations in response to a reiterated water deficit during a vegetative (non-productive) and a fruiting (productive) period. In addition, we evaluated the concentration of tocochromanols in achenes (true fruits) and flesh of strawberries (whole fruits) at the white and full-red stages both under optimal and stress conditions. Results showed that leaves mainly accumulated α-tocopherol, with plastochromanol-8 and γ-tocopherol being present at low amounts. In contrast, whole fruits did not accumulate plastochromanol-8, γ-tocopherol being the major tocochromanol in the achenes (true fruit) and α-tocopherol in the flesh. While α-tocopherol content in leaves increased up to seven-fold after 12 weeks of stress during the fruiting period, it kept unaltered during the vegetative period. Neither plastochromanol-8 nor γ-tocopherol contents increased in leaves of stressed plants. During the fruiting period, γ-tocopherol content increased in whole fruits of stressed plants (most of it being accumulated in the achenes). Among the compounds examined, the flesh of strawberries accumulated α-tocopherol only, both at the white and full-red stages. It is concluded that (i) α-tocopherol is the major tocochromanol in leaves, while γ-tocopherol is the major tocochromanol in achenes (ii) reiterated water deficit promotes the accumulation of α-tocopherol in leaves and γ-tocopherol in fruits, (iii) α-tocopherol not only accumulates in photosynthetic tissues (leaves and whole fruits at green stages), but also in non-photosynthetic tissues (flesh of whole fruits at the white and full-red stages), and (iv) achenes (true fruits) of strawberry plants are an extraordinary rich source of tocopherols.