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Marigold (Tagetes erecta L.) is an important ornamental plant with a wide variety of flower colors. Despite its economic value, few biochemical and molecular studies have explored the generation of flower color in this species. To study the mechanism underlying marigold petal color, we performed a metabolite analysis and de novo cDNA sequencing on the inbred line ‘V-01’ and its petal color mutant ‘V-01M’ at four flower developmental stages. A total of 49,217 unigenes were identified from 24 cDNA libraries. Based on our metabolites and transcriptomic analyses, we present an overview of carotenoid biosynthesis, degradation, and accumulation in marigold flowers. The carotenoid content of the yellow mutant ‘V-01M’ was higher than that of the orange inbred line ‘V-01’, and the abundances of the yellow compounds lutein, neoxanthin, violaxanthin, zeaxanthin, and antheraxanthin were significantly higher in the mutant. During flower development, the carotenoid biosynthesis genes were upregulated in both ‘V-01’ and ‘V-01M’, with no significant differences between the two lines. By contrast, the carotenoid degradation genes were dramatically downregulated in the yellow mutant ‘V-01M’. We therefore speculate that the carotenoid degradation genes are the key factors regulating the carotenoid content of marigold flowers. Our research provides a large amount of transcriptomic data and insights into the marigold color metabolome.

Xanthophylls in light harvesting complexes perform a number of functions ranging from structural support to light-harvesting and photoprotection. In the major light harvesting complex of photosystem II in plants (LHCII), the innermost xanthophyll binding pockets are occupied by lutein molecules. The conservation of these sites within the LHC protein family suggests their importance in LHCII functionality. In the present work, we induced the photoprotective switch in LHCII isolated from the Arabidopsis mutant npq1lut2, where the lutein molecules are exchanged with violaxanthin. Despite the differences in the energetics of the pigments and the impairment of chlorophyll fluorescence quenching in vivo, we show that isolated complexes containing violaxanthin are still able to induce the quenching switch to a similar extent to wild type LHCII monomers. Moreover, the same spectroscopic changes take place, which suggest the involvement of the terminal emitter site (L1) in energy dissipation in both complexes. These results indicate the robust nature of the L1 xanthophyll binding domain in LHCII, where protein structural cues are the major determinant of the function of the bound carotenoid.

Chickpea being a winter season crop often experiences heat stress during reproductive phase. For chickpea production, terminal heat stress is one of the major constraints. Plants have built up numerous mechanisms to combat the heat stress. We considered the photosynthetic pigments for heat tolerance. Therefore, in order to investigate the heat tolerance in relation to photosynthetic pigments, a field trial was carried out having 4 contrasting genotypes namely BG 240 and JG 14 (relatively heat tolerant), SBD 377 (moderately tolerant) and ICC 1882 (relatively heat sensitive). Heat stress was imposed by altering the sowing date i.e. normal (18th November) and late sown (18th December). Under delayed sown condition, heat stress was faced by crop starting from flowering stage to crop maturity. Under heat stress condition, heat tolerant genotypes BG 240 and JG 14 maintained higher level of membrane stability, RWC (%), osmolytes, dry matter partitioning, grain yield, heat tolerance index and had higher values of zeaxanthin, quantum yield of PS II (Fv/Fm ratio), non-photochemical quenching (NPQ), photosynthetic rate, level of photosynthetic pigments (chlorophylls and carotenoids) and lower level of violaxanthin, and lipid peroxidation as compared to heat sensitive one (ICC 1882). In addition to this, Fv/Fm ratio and NPQ exhibited positive relationship with heat tolerance which suggested the involvement of xanthophyll cycle pigments in chickpea heat tolerance.

Optimizing the photoprotection of different leaves as a whole is important for plants to adapt to fluctuations in ambient light conditions. However, the molecular basis of this leaf-to-leaf communication is poorly understood. Here, we used a range of techniques, including grafting, chlorophyll fluorescence, revers transcription quantitative PCR, immunoblotting, chromatin immunoprecipitation, and electrophoretic mobility shift assays, to explore the complexities of leaf-to-leaf light signal transmission and activation of the photoprotective response to light fluctuation in tomato (Solanum lycopersicum). We established that light perception in the top leaves attenuated the photoinhibition of both PSII and PSI by triggering photoprotection pathways in the bottom leaves. Local light promoted the accumulation and movement of LONG HYPOCOTYL5 from the sunlit local leaves to the systemic leaves, priming the photoprotective response of the latter to light fluctuation. By directly activating the transcription of PROTON GRADIENT REGULATION5 and VIOLAXANTHIN DE-EPOXIDASE, LONG HYPOCOTYL5 induced cyclic electron flow, the xanthophyll cycle, and energy-dependent quenching. Our findings reveal a systemic signaling pathway and provide insight into an elaborate regulatory network, demonstrating a pre-emptive advantage in terms of the activation of photoprotection and, hence, the ability to survive in a fluctuating light environment.

Dynamics of chlorophyll a fluorescence changes (including JIP test parameters) and photosynthetic pigments were studied in oat (Avena sativa L.) leaves of late summer sowing during autumnal cooling. As the average daily temperature decreased from 8 to 2°С, the chlorophyll content decreased by 40%, while the chlorophyll a/b ratio ranged between 2.2 and 2.4. The total pool of carotenoids and the relative content of β‑carotene, lutein, neoxanthin, and pigments of the violaxanthin cycle changed insignificantly. The relative number of QB-nonreducing reaction centers (RC) of photosystem II (PSII) and the quantum yield of energy-dependent component qE of nonphotochemical quenching in the PSII antenna (φNPQ parameter) were found to increase during the seasonal cooling. The values of Fv/Fm parameter characterizing the maximal photochemical efficiency of PSII complexes were 0.72–0.76. At temperatures around 0°C, Fv/Fm decreased to 0.62. At the same time, the nonregulated (light-independent) thermal dissipation (photoinhibitory component qI of nonphotochemical quenching) was enhanced, which was manifested in the increase in parameters φDo and DI0/RC. It is concluded that, under seasonal cooling, the PSII reaction centers partly lose photochemical activity and start functioning as dissipative centers of excitation energy. In a significant part of inactivated RC, the loss of QA-reduction was reversible, which implies the formation of photoinactivated forms of PSII complexes stabilized at low temperatures. The decrease in daily average temperatures to −3°С with nighttime low temperatures from −7 to −8°С led to plant death within 3 days.

The present study investigated how different storage conditions affect antioxidant levels in three scab-resistant and powdery mildew-tolerant apple cultivars. The contents of carotenoids, along with free and glycosylated phenolic acids, were quantified in harvested apples and apples stored in boxes with controlled atmospheric conditions (1.2% O2 and 2.2% CO2) and temperature (1 °C), boxes with regulated temperature (1 °C) and storage rooms with a temperature between 1 and 4 °C. All three cultivars demonstrated a continuous decrease in total carotenoid content (sum of s-carotene, lutein, neoxanthin, violaxanthin, zeaxanthin and antheraxanthin) during the storage period. However, apples stored under controlled atmospheric conditions showed significantly higher carotenoid levels than apples stored under other approaches over 3 and 5 months of storage. Although the storage approach clearly affected carotenoid levels across the three tested cultivars, the ratio between the levels of individual carotenoids was neither affected by storage approach nor cultivar. Free phenolic acid contents were found to be cultivar specific; whereas, all three cultivars demonstrated similar glycosylated phenolic acid contents. Chlorogenic acid was the most common free phenolic acid in all three cultivars, while protocatechuic and caffeic acid were the dominant glycosylated phenolic acids identified from the cultivars. Interestingly, stored apples showed higher free phenolic acid levels than harvested apples; while, both harvested and stored apples showed similar concentrations of glycosylated phenolic acids. As such, none of the three tested storage conditions had a pronounced effect on either group of phenolic acids (total content or concentrations of individual compounds).

The accumulation of carotenoids (carotenogenesis) in the cells of Haematococcus pluvialis (strain IBCE H-17) upon cultivation in nutrient media deficient in nutrient elements (N and K + P) is shown. K and P deficiency in nutrient medium led to accumulation of astaxanthin, β-carotene, anteraxanthin, zeaxanthin and violaxanthin after 18 days of cultivation, while the amount of neoxanthin and lutein was at the control level. Carotenogenesis under such conditions was accompanied by high levels of chlorophyll (a + b). The use of nutrient medium deficient in N led to the accumulation of astaxanthin and, to a lesser extent, β-carotene in haematococcus cells, while lutein, anteraxanthin, zeaxanthin, violaxanthin and neoxanthin levels were lower or the same as control. N deficiency caused the decrease in amount of chlorophyll (a + b). Nitrogen deficiency was 4.3 times more effective than control medium and 1.8 times more effective than combined potassium and phosphorus deficiency in promoting astaxanthin accumulation.

Microbial production of carotenoids has mainly focused towards a few products, such as β-carotene, lycopene and astaxanthin. However, other less explored carotenoids, like violaxanthin, have also shown unique properties and promissory applications. Violaxanthin is a plant-derived epoxidated carotenoid with strong antioxidant activity and a key precursor of valuable compounds, such as fucoxanthin and β-damascenone. In this study, we report for the first time the heterologous production of epoxycarotenoids in yeast. We engineered the yeast Saccharomyces cerevisiae following multi-level strategies for the efficient accumulation of violaxanthin. Starting from a β-carotenogenic yeast strain, we first evaluated the performance of several β-carotene hydroxylases (CrtZ), and zeaxanthin epoxidases (ZEP) from different species, together with their respective N-terminal truncated variants. The combined expression of CrtZ from Pantoea ananatis and truncated ZEP of Haematococcus lacustris showed the best performance and led to a yield of 1.6 mg/gDCW of violaxanthin. Further improvement of the epoxidase activity was achieved by promoting the transfer of reducing equivalents to ZEP by expressing several redox partner systems. The co-expression of the plant truncated ferredoxin-3, and truncated root ferredoxin oxidoreductase-1 resulted in a 2.2-fold increase in violaxanthin yield (3.2 mg/gDCW). Finally, increasing gene copy number of carotenogenic genes enabled reaching a final production of 7.3 mg/gDCW in shake flask cultures and batch bioreactors, which is the highest yield of microbially produced violaxanthin reported to date.

The violaxanthin (V)-antheraxanthin (A)-zeaxanthin (Z) (VAZ) cycle was deemed a non-second-scale process of photoprotection in higher plants and microalgae, but the validity of this view has not been confirmed. To test this view, we explored responses of the VAZ cycle and the relationship between the VAZ cycle and non-photochemical quenching (NPQ) under highlight at second and minute scales in Heterosigma akashiwo and Platymonas sp. Both A and Z were generated in H. akashiwo during 15 s of light exposure, whereas only A rapidly accumulated within 15 s of exposure in Platymonas sp. The above results, together with a time-dependent sigmoidal relationship between the VAZ cycle (de-epoxidation state, A/Chl a, and Z/Chl a) and NPQ, proved that the VAZ cycle was a second-scale process related to NPQ. In addition, we found that not all NPQ was dependent on the VAZ cycle and suggested that NPQ model should be carefully modified due to the species-specific proportions of de-epoxidation-dependent NPQ.

Non-photochemical quenching (NPQ) is one of the most important photo-protection mechanisms in brown macroalgae. Global warming and ocean acidification are predicted to impact physiological characteristics of marine algae. However, little is known about the effects of co-occurrence of the elevation of pCO2 and temperature on photochemical capacity, especially regarding photoprotective mechanisms in brown macroalgae. Here, we studied the separate and combined effects of increases in pCO2 and temperature on the photochemical characteristics and growth performance in sporophytes of the brown macroalga Saccharina japonica. The results showed that the NPQ of S. japonica is mainly dependent on the xanthophyll cycle (XC) which appears to be related only to the activation of the enzyme violaxanthin de-epoxidase (VDE), and the transthylakoid proton gradient (ΔpH) could not induce NPQ alone. The elevation of pCO2 reduced NPQ value of S. japonica under high-temperature stress. After 60-day cultivation under the ambient and elevated pCO2 (400 and 1000 μatm), we further found that the elevation of pCO2 promoted growth and increased the photosynthetic performance of all three cultivar strains of S. japonica that have been traditionally cultured for many years in China.

Recombinant Escherichia coli cells, which express the higher-plant CaZEP (zeaxanthin epoxidase) and AtCYO1 (molecular chaperone) genes and an NADPH regeneration system in addition to the IDI, crtE, crtB, crtI, crtY, and crtZ genes for zeaxanthin biosynthesis, were cultured in 2 × YT medium for the efficient production of antheraxanthin and violaxanthin. The carotenoids accumulated in the cells were purified by two-phase partition, silica gel column chromatography, and preparative silica gel HPLC. Mass spectrometry and nuclear magnetic resonance analyses of these carotenoids revealed that a novel carotenoid, determined to be (3R,6′S)-3,6′-dihydroxy-β,e-caroten-3′-one and named as 6′-hydroxy-3′-didehydrolutein, was produced in addition to zeaxanthin, antheraxanthin and violaxanthin. It is likely that the new carotenoid was generated from an unstable epoxy-carotenoid antheraxanthin that was synthesized from zeaxanthin with CaZEP. Its antioxidant activities were also examined.

Heatwaves are becoming more frequent with climate warming and can impact tree growth and reproduction. Eucalyptus parramattensis can cope with an extreme heatwave in the field via transpiratory cooling and enhanced leaf thermal tolerance that protected foliar tissues from photo-inhibition and photo-oxidation during natural midday irradiance. Here, we explored whether changes in foliar carotenoids and/or the xanthophyll cycle state can facilitate leaf acclimation to long-term warming and/or an extreme heatwave event. We found that leaves had similar carotenoid levels when grown for one year under ambient and experimental long-term warming (+ 3 °C) conditions in whole tree chambers. Exposure to a 4-day heatwave (> 43 °C) significantly altered the xanthophyll de-epoxidation state of carotenoids revealing one mechanism by which trees could minimise foliar photo-oxidative damage. The levels of zeaxanthin were significantly higher in both young and old leaves during the heatwave, revealing that violaxanthin de-epoxidation and perhaps de novo zeaxanthin synthesis contributed to enhancement of the xanthophyll cycle state. In a future climate of long-term warming and increased heatwave events, leaves of E. parramattensis will be able to utilise biochemical strategies to alter the xanthophyll cycle state and cope with extreme temperatures under natural solar irradiation.

Carotenoids are a class of natural product compound that are currently being used as colouring agents and widely used in food industry. Carotenoids are bioactive pigments obtained mainly from plants through dietary intake. They possess good features in terms of dietary supplement, food colourant, and polymer stabiliser. The presence of 4 main carotenoids, which are β-carotene, zeaxanthin, lutein, and violaxanthin, were determined in 4 classes of allelopathic plant groups namely trees, ferns, grasses and herbaceous plants. This research aims to explore the carotenoid’s content and composition in 11 allelopathic species by HPLC analysis. A. auriculiformis (tree) was found to have the highest total carotenoid concentration (146.36 µg/g DW) that was substantially higher than all other species tested whereas the lowest total carotenoid concentration was found in S. palustris (fern) (3.76 µg/g DW). Lutein and β-carotene were detected highest in A. auriculiformis (tree), with 1024 ± 25.5 µg/g DW and 37.55 ± 3.16 µg/g DW, respectively. Violaxanthin and zeaxanthin were found substantially highest in M. cajuputi (tree) (5.02 ± 0.5 µg/g DW) and S. palustris (fern) (5.88 ± 0.19µg/g DW), respectively.

We present the results of experiments on the influence of feeding the marine bivalve mollusk Cerastoderma glaucum (Bruguiere, 1789) with a monoculture of the green algae Tetraselmis viridis on the composition of carotenoids in its tissues. The carotenoid repertoire of C. glaucum was found to include β-carotene, alloxanthin, lutein, diadinoxanthin, neoxanthin, fucoxanthin, heteroxanthin, mactraxanthin and four carotenoid esters, with mactraxanthin being specific to C. glaucum. In T. viridis, carotenoids were represented by β, e -carotene, lutein, zeaxanthin, violaxanthin, neoxanthin. A 6-day microalgal mono-diet led to an increase in the total carotenoid content in mollusk tissues, mainly at the expense of pigments characteristic of T. viridis. The process was accompanied by a decrease in the concentration of other plant carotenoids and mactraxanthin isomerization. Despite the changes in the accumulation and transformation of carotenoids, the experiment led to a 20% death rate among individuals, indicating an adverse effect of a monotonous diet on mollusks.

Kaolin-particle film has been considered a low-cost technology to mitigate the adverse effects of high light and temperature, and drought in several crops. However, the underlying excess energy absorption and dissipation mechanisms, and related components associated with kaolin photoprotective effects in grapevines are poorly explored. This study aims to understand the interactions between kaolin foliar treatment and photosynthetic pigments accumulation, carotenoids metabolism, xanthophyll cycle regulation, and its putative role on the non-photochemical quenching (NPQ) processes in Touriga-Franca (TF) and Touriga-Nacional (TN) varieties. The experiments were conducted during the 2017 summer season in a commercial vineyard, and measurements were performed at pre-dawn and midday in each sampling date (EL35 – veraison; EL38 – full mature). Overall, TF variety showed higher accumulation of chlorophylls, xanthophylls, and de-epoxidation state (DPS) than TN. Kaolin treatment enhanced TN chlorophyll accumulation up to 114 % at EL35 (veraison) and 123 % at EL38 (full mature), highlighting its protective role on chlorophyll degradation, while no changes were found in TF, which might indicate a lower need for particle-film technology in this variety under the current environmental conditions. Individual carotenoids were mainly higher in the treated leaves of both varieties, as well as the xanthophyll cycle pigments zeaxanthin (Zx) and violaxanthin (Vx). Simultaneously, the DPS and NPQ values were lower in TN and TF treated leaves (1.92 – 2.36) compared to untreated vines (3.19 – 3.24), suggesting that there might be other components influencing NPQ levels beyond Zx, with an indirect role in long-lasting NPQ processes. In addition, in the TF kaolin-treated leaves, violaxanthin de-epoxidase (VvVDE1) and zeaxanthin epoxidase (VvZEP1) gene expression were respectively 3-fold and 4-fold upregulated at stage EL35, while VvZEP1 gene expression decreased at stage EL38 in TN kaolin-treated leaves, indicating an optimised regulation of the xanthophyll cycle. These findings suggest that kaolin treatment promoted a fine-tuning of grapevine summer stress responses under sustained summer stress factors, by managing xanthophyll cycle dynamics, and pigments accumulation., This work was supported by National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020, the Clim4Vitis project – "Climate change impact mitigation for European viticulture: knowledge transfer for an integrated approach", funded by European Union's Horizon 2020 research and innovation programme, under grant agreement no. 810176. Authors acknowledge Rui Flores from “Herdade do Esporão”, for the collaboration and efforts in making the vineyard facilities available for this study, as well as BASF collaboration, namely Paulo Matos. The technical assistance of Inmaculada Carbonell (IATA-CSIC) in pigment analysis is also gratefully acknowledged. Sara Bernardo acknowledges the financial support provided by the FCT-Portuguese Foundation for Science and Technology (PD/BD/ 128273/2017), under the Doctoral Programme "Agricultural Production Chains – from fork to farm", and Dinis L.-T. thanks the FCT and UTAD for the research contract (D.L. Law no. 57/2017).

Chlorella gloriosa (Chlorellaceae, Trebouxiophyceae) was isolated from seawater off the coast of the Dokdo Islands in Korea. An axenic culture was established using the streak-plate method on f/2 agar media supplemented with antibiotics, allowing identification of the isolate by morphological, molecular, and physiological analyses. The morphological characteristics observed by light and electron microscopy revealed typical morphologies of C. gloriosa species. The molecular phylogenetic inference drawn from the small-subunit 18S rRNA sequence verified that the microalgal strain belongs to C. gloriosa. Additionally, gas chromatography-mass spectrometry analysis showed that the isolate was rich in nutritionally important omega-3 and -6 polyunsaturated fatty acids and high-performance liquid chromatography analysis revealed that the high-value antioxidants lutein and violaxanthin were biosynthesized as accessory pigments by this microalga, with arabinose, galactose, and glucose as the major monosaccharides. Therefore, in this study, a Korean marine C. gloriosa species was discovered, characterized, and described, and subsequently added to the national culture collection.

Background Carotenoids are a class of terpenoid pigments that contribute to the color and nutritional value of many fruits. Their biosynthetic pathways have been well established in a number of plant species; however, many details of the regulatory mechanism controlling carotenoid metabolism remain to be elucidated. Apricot is one of the most carotenoid-rich fruits, making it a valuable system for investigating carotenoid metabolism. The purpose of this study was to identify key genes and regulators associated with carotenoid metabolism in apricot fruit based on transcriptome sequencing. Results During fruit ripening in the apricot cultivar ‘Luntaixiaobaixing’ (LT), the total carotenoid content of the fruit decreased significantly, as did the levels of the carotenoids β-carotene, lutein and violaxanthin (p NCED1, CCD1/4, PIF3/4, HY5, ERF003/5/12, RAP2–12, AP2, AP2-like, BZR1, MADS14, NAC2/25, MYB1R1/44, GLK1/2 and WRKY6/31/69) potentially affect apricot carotenoid metabolism during ripening. Based on deciphering the molecular mechanism involved in ripening, a network model of carotenoid metabolism in apricot fruit was proposed. Conclusions Overall, our work provides new insights into the carotenoid metabolism of apricot and other species, which will facilitate future apricot functional studies and quality breeding through molecular design.

Cera pepper ( Capsicum pubescens ) is an exotic fruit considered as a rich source of nutraceuticals with known benefits for human health and also an economic resource for local producers in Mexico. The present investigation reports on the in vitro and in situ antifungal activity of the essential oil from Mentha piperita and its two major volatiles (menthol and menthone) against Fusarium sambucinum , which is a causal agent of soft rot in cera pepper. The application of these components in pepper fruits previously infected with F. sambucinum caused a significant delay (p < 0.05) in the emergence of soft rot symptoms. This effect was reflected in the maintenance of pH and fruit firmness during a period of 10 days. The nutrimental content of the fruits (protein, fiber, fat and other proximate parameters) was conserved in the same period of time. The nutraceutical content of these fruits was estimated by the quantification of seven carotenoids (violaxanthin, cis-violaxanthin, luteoxanthin, antheraxanthin, lutein, zeaxanthin and beta-carotene), ascorbic acid and capsaicinoids (capsaicin and dihydrocapsaicin). According to our results, the essential oil from M. piperita and its major volatiles exerted a preservative effect on these metabolites. Our findings demonstrated that the essential oil of M. Piperita and its major volatiles represent an ecological alternative for the control of fusariosis caused by F. sambucinum in cera peppers under postharvest conditions.

Nutrient deficiency is known to constrain plant growth in numerous ways, but how it impacts floral displays and pollination success remains unclear. Here we investigate how insufficient availability of sulphur – a vital plant nutrient that is a limiting factor in natural and agricultural regions throughout the world – influences the production of floral displays in Brassica rapa, Physalis philadelphica and three Petunia species with differently coloured flowers. Sulphur deficiency led to a drastic reduction in the number of open flowers, an aberrant flower morphology and smaller pollen with an altered mineral nutrient content. Intriguingly, sulphur deprivation also led to a clear reduction in pigmentation of yellow flowers, but not in flowers with white, purple and red colours. The pale yellow flower colour was due to decreased amounts of violaxanthin, lutein and other carotenoids, suggesting that the carotenoid synthesis pathway is particularly susceptible to sulphur deficiency. Additional experiments with nitrogen and phosphorus depletion confirmed that observed colour and morphological changes were not a general nutrient limitation response, but could be ascribed to sulphur depletion specifically. Taken together, our results showed that (mild) sulphur deficiency deteriorates a suite of floral traits, and that the effects may cascade to pollinators and so have the potential to undermine (agro-)ecosystem functioning.

OsVDE, a lipocalin-like protein in chloroplasts, negatively regulated the ABA biosynthesis and stomatal closure under salt stress in rice seedlings. Violaxanthin de-epoxidase (VDE) is a key enzyme of xanthophyll cycle. It plays a critical role in abscisic acid (ABA) biosynthesis, growth and stress responses in plants. Although functions of several VDE genes have been characterized, it is largely unknown whether OsVDE regulates the ABA biosynthesis and salt stress tolerance in rice. In this study, we generated the OsVDE overexpressing and CRISPR-Cas9-mediated gene-editing transgenic lines, and identified that the gene-editing mutant lines showed the dwarfism, shorter panicle and lower seed-setting rate than the wild type whereas the overexpression lines did not exhibit the difference from the wild type. In addition, the gene-editing transgenic lines were hypersensitive to exogenous ABA during germination. Under salt stress, the gene-editing transgenic seedlings had a higher ABA level, higher stomatal closure percentage and higher survival rate than the wild type. The qRT-PCR analysis confirmed that OsVDE negatively regulated the OsNECD2/4/5 expressions, ABA biosynthesis and salt stress tolerance in rice seedlings. These results provide new evidence that VDE plays an essential role in ABA biosynthesis and salt stress tolerance in plants.

Bryopsidales (Chlorophyta) are cultured and consumed in several regions of the planet and are known for their high nutritional value and bioprospection potential, due to a high content of relevant polar lipids and polysaccharides. Among other characteristic features, these marine algae are known for possessing unique photosynthetic pigment-protein complexes and for the absence (in nearly all species investigated) of a functional xanthophyll cycle, a ubiquitous photoprotection mechanism present in most algae and plants. With the aim of characterizing the photophysiology of this atypical group of algae, we investigated the changes in pigment content and polar lipidome of two Bryopsidales species (Codium tomentosum and Bryopsis plumosa) exposed for 7 days to low or high irradiance (20 vs. 1,000 μmol photons m–2 s–1). Our results show that high light has a strong effect on the pigment composition, triggering the time-dependent accumulation of all-trans-neoxanthin (t-Neo) and violaxanthin (Viola). High light-acclimated macroalgae also displayed a shift in the characteristic polar lipidome, including a trend of accumulation of lyso-glycolipids, and highly unsaturated phospholipids and betaine lipids. We hypothesize that the observed shifts on the lipid composition could promote the interaction between t-Neo and Viola with the siphonaxanthin–chlorophyll–protein complexes (SCP) of photosystem II (PSII) within the thylakoid membranes of the chloroplasts. Light induced changes in pigment and lipid composition could contribute to the fitness of Bryopsidales algae by reducing damages to the photosynthetic apparatus under increased irradiance.

To determine the role of α- and γ-tocopherol (TC), this study compared the response to salt stress (200 mM NaCl) in wild type (WT) Arabidopsis thaliana (L.) Heynh. And its two mutants: (1) totally TC-deficient vte1, (2) vte4 accumulating γ-TC instead of α-TC, and (3) tmt transgenic line overaccumulating α-TC. Raman spectra revealed that salt-exposed α-TC accumulating plants were more flexible in regulating chlorophyll, carotenoid and polysaccharide levels than TC deficient mutants, while the plants overaccumulating γ-TC had the lowest levels of these biocompounds. Tocopherol composition and NaCl concentration affected xanthophyll cycle by changing the rate of violaxanthin de-epoxidation and zeaxanthin formation. NaCl treated plants with altered TC composition accumulated less oligosaccharides than WT plants. α-TC deficient plants increased their oligosaccharide levels and reduced maltose amount, while excessive accumulation of α-TC corresponded with enhanced amounts of maltose. Salt-stressed TC-deficient mutants and tmt transgenic line exhibited greater proline levels than WT plants, lower chlorogenic acid levels, and lower activity of catalase and peroxidases. α-TC accumulating plants produced more methylated proline- and glycine- betaines, and showed greater activity of superoxide dismutase than γ-TC deficient plants. Under salt stress, α-TC demonstrated a stronger regulatory effect on carbon- and nitrogen-related metabolites reorganization and modulation of antioxidant patterns than γ-TC. This suggested different links of α- and γ-TCs with various metabolic pathways via various functions and metabolic loops.

Main conclusion The compatible solute sucrose reduces the efficiency of the enzymatic de-epoxidation of violaxanthin, probably by a direct effect on the protein parts of violaxanthin de-epoxidase which protrude from the lipid phase of the thylakoid membrane. The present study investigates the influence of the compatible solute sucrose on the violaxanthin cycle of higher plants in intact thylakoids and in in vitro enzyme assays with the isolated enzyme violaxanthin de-epoxidase at temperatures of 30 and 10 °C, respectively. In addition, the influence of sucrose on the lipid organization of thylakoid membranes and the MGDG phase in the in vitro assays is determined. The results show that sucrose leads to a pronounced inhibition of violaxanthin de-epoxidation both in intact thylakoid membranes and the enzyme assays. In general, the inhibition is similar at 30 and 10 °C. With respect to the lipid organization only minor changes can be seen in thylakoid membranes at 30 °C in the presence of sucrose. However, sucrose seems to stabilize the thylakoid membranes at lower temperatures and at 10 °C a comparable membrane organization to that at 30 °C can be observed, whereas control thylakoids show a significantly different membrane organization at the lower temperature. The MGDG phase in the in vitro assays is not substantially affected by the presence of sucrose or by changes of the temperature. We conclude that the presence of sucrose and the increased viscosity of the reaction buffers stabilize the protein part of the enzyme violaxanthin de-epoxidase, thereby decreasing the dynamic interactions between the catalytic site and the substrate violaxanthin. This indicates that sucrose interacts with those parts of the enzyme which are accessible at the membrane surface of the lipid phase of the thylakoid membrane or the MGDG phase of the in vitro enzyme assays.

In this study, astaxanthin yield of Phaffia rhodozyma PR106 increased significantly under titanium dioxide (TiO2) stress, and the yield of lycopene and β-carotene also increased significantly, as well as the yield of violaxanthin and lutein significantly decreased; in addition, TiO2 stress promoted cell division and changed cell morphology of PR106. Then, the mechanism of increasing astaxanthin yield was studied by transcriptomics and related metabolic regulation. The results showed that astaxanthin accumulation in PR106 was not directly related to mRNA transcription and post-translational modifications regulation under TiO2 stress; TiO2 stress accelerated glucose uptake of yeast, promoted reuse of ethanol, and increased the formation of acetyl-CoA and ATP. The more carbon flux was shifted to astaxanthin synthesis pathway and weakened carotenoids accumulation in astaxanthin branch pathway to improve the astaxanthin production of PR106. The metabolism regulation of ROS could continue in the PR106 strain.

Chinese kale (Brassica oleracea var. alboglabra) is rich in carotenoids, and neoxanthin is one of the most important carotenoids in Chinese kale. In this study, the function of the neoxanthin synthase gene (BoaNXS) in Chinese kale was investigated. BoaNXS, which had a 699-bp coding sequence, was cloned from the white flower cultivar of Chinese kale and was expressed in all developmental stages and organs of Chinese kale, its expression was highest in young seeds. The subcellular localization indicated that BoaNXS was localized in the chloroplast. BoaNXS-overexpressed plants were obtained via Agrobacterium-mediated transient overexpression methodology, and the gene overexpression efficiencies ranged from 2.10- to 4.24-fold. The color in the leaves of BoaNXS-overexpressed plants changed from green to yellow-green, the content of total and individual carotenoids, such as neoxanthin, violaxanthin, and lutein, was significantly increased, and the expression levels of most carotenoid biosynthetic genes were notably increased. These findings indicated that BoaNXS is of vital importance in carotenoid biosynthesis in Chinese kale and could be used as a candidate gene for enriching the carotenoid accumulation and color of Chinese kale and other Brassica vegetables.

Thioredoxin-like protein CDSP32 (Trx CDSP32), a thioredoxin-like (Trx-like) protein located in the chloroplast, can regulate photosynthesis and the redox state of plants under stress. In order to examine the role of Trx CDSP32 in the photosynthetic apparatus of plants exposed to cadmium (Cd), the effects of Trx CDSP32 on photosynthetic function and photoprotection in tobacco leaves under Cd exposure were studied using a proteomics approach with wild-type (WT) and Trx CDSP32 overexpression (OE) tobacco plants. Cd exposure reduced stomatal conductance, blocked PSII photosynthetic electron transport, and inhibited carbon assimilation. Increased water use efficiency (WUE), cyclic electron flow (CEF) of the proton gradient regulation 5 pathway (PGR5-CEF), and regulated energy dissipation [Y(NPQ)] are important mechanisms of Cd adaptation. However, CEF of the NAD(P)H dehydrogenase pathway (NDH-CEF) was inhibited by Cd exposure. Relative to control conditions, the expression levels of violaxanthin de-epoxidase (VDE) and photosystem II 22 kDa protein (PsbS) in OE leaves were significantly increased under Cd exposure, but those in WT leaves did not change significantly. Moreover, the expression of zeaxanthin epoxidase (ZE) under Cd exposure was significantly higher than that in WT leaves. Thus, Trx CDSP32 increased Y(NPQ) and alleviated PSII photoinhibition under Cd exposure. Trx CDSP32 not only increased PGR5-like protein 1A and 1B expression, but also alleviated the down-regulation of NAD(P)H-quinone oxidoreductase subunits induced by Cd exposure. Thus, Trx CDSP32 promotes CEF in Cd-exposed tobacco leaves. Thus, Trx CDSP32 alleviates the Cd-induced photoinhibition in tobacco leaves by regulating two photoprotective mechanisms: CEF and xanthophyll cycle-dependent energy dissipation.

Tetraselmis suecica is a green microalga that thrives under a wide range of conditions, used in the commercial culture of fish, mollusk, and crustacean larvae for supplementing the demand for fertilizers. Its pigments have applications in human health care as drug products, vitamins, and cosmetics. Growth and pigment concentration of T. suecica were evaluated in experimental cultures with different nutrient concentrations and light intensities to determine the most appropriate culture conditions to optimize the production of biomass and pigments. Chlorophyll-a, chlorophyll-b, lutein, violaxanthin, α, β-carotene, and neoxanthin concentrations were evaluated under three different nutrient conditions (441.5/18.1, 883/36.3, and 1766/76.2 μM of NaNO3/NaH2PO4) and four light intensities (50, 150, 300, and 750 μmol quanta m−2 s−1). Increases in either or both of these factors lead to increases in the concentration of all pigments. Chlorophyll-a reached up to 5×103 mg m−3, chlorophyll-b up to 2500 mg m−3, lutein 600 mg m−3, violaxanthin 300 mg m−3, α, β-carotene 500 mg m−3, and neoxanthin 400 mg m−3. Growth rate (μ) attained values of 1.6 d−1. An index to evaluate the efficiency of pigment production by light intensity (called LER) was computed. The highest LER was recorded at 50 μmol quanta m−2 s−1 and a nutrient concentration of 1766/76.2 μM (NaNO3/NaH2PO4); this treatment optimizes pigment production with the lowest light intensity. Our results show that the optimum light intensity should be selected according to the objective of the culture, either maximizing pigment concentration for harvesting at higher concentrations or reducing production costs regarding light consumption.