The effects of moderately high temperature on zeaxanthin accumulation and decay

Association analysis of maize stem vascular bundle micro-characteristics with yield components based on micro-CT and identification of related genes

The distribution pattern of vascular bundles and microstructure characteristics significantly impact crop yield. Previous studies have primarily focused on investigating the micro-phenotypic characteristics and genetic regulation of individual internode, neglecting the exploration of the relationship between different internodes. This study, for the first time, comprehensively analyzed multi-scale phenotypic information of stem cross-sections, zones, and vascular bundles in three different internodes (basal third internode, ear internode and highest internode) of 268 inbred maize lines using Micro-computed tomography scanning. Key findings revealed that basal third internode and ear internode exhibited more stable microscopic characteristics than highest internode. Inbred lines with higher numbers of vascular bundle and well-developed inner zone in ear internode exhibited better yield characteristics, particularly in the kernel number per row. Genome-wide association analysis respectively identified 15, 1 and 1 putative candidate genes in basal third internode, ear internode and highest internode. These genes encode a variety of enzymes, such as oxidases, synthetases, ligase enzyme and protein kinases. Notably, Zm00001d042490 may be an important putative candidate gene for The number of vascular bundles in the periphery zone and corn grain traits. This study provides an important theoretical basis and genetic resources for accurately identifying different internode phenotypes of maize stalks, potentially advancing the selection of high-yielding, high-quality maize varieties.

Synergistic effects of temperature and light on photoprotection in the model diatom Phaeodactylum tricornutum

Diatoms dominate phytoplankton communities in turbulent waters, where light fluctuations can be frequent and intense. Due to this complex environment, these heterokont microalgae display remarkable photoprotection strategies, including a fast Non-Photochemical Quenching (NPQ). However, in nature, several abiotic parameters (such as temperature) can influence the response of photosynthetic organisms to light stress in a synergistic or antagonistic manner. Yet, the combined effects of light and these other drivers on the photosynthetic and photoprotective capacity of diatoms are still poorly understood. In this work, we investigated the impact of short-term temperature and light stress on the model diatom Phaeodactylum tricornutum, combining NPQ induction-recovery assays or light curves with a broad gradient of superimposed temperature treatments (5 to 35°C). We employed mutant lines deficient in NPQ generation (vde KO) or recovery (zep3 KO) and wild type. We found that temperature and light have a synergistic effect: lower temperatures limited both the photosynthetic capacity and NPQ, while the general photophysiological performance was enhanced with warming, up to a heat-stress limit (above 30°C). We discuss the temperature effects on NPQ induction and recovery and propose that these are independent from the energy requirements of the cells and result from altered xanthophyll cycle dynamics. Namely, we found that de-epoxidation activity strongly increases with temperature, outweighing epoxidation and resulting in a positive increase of NPQ with temperature. Finally, we propose that in a short-term time frame, temperature and light have a synergistic and not antagonistic effect, with a positive relationship between increasing temperature and NPQ.

Light Drives and Temperature Modulates: Variation of Phenolic Compounds Profile in Relation to Photosynthesis in Spring Barley

Accumulation and metabolic profile of phenolic compounds (PheCs; serving as UV-screening pigments and antioxidants) as well as carbon fixation rate (A_n) and plant growth are sensitive to irradiance and temperature. Since these factors are naturally co-acting in the environment, it is worthy to study the combined effects of these environmental factors to assess their possible physiological consequences. We investigated how low and high irradiance in combination with different temperatures modify the metabolic profile of PheCs and expression of genes involved in the antioxidative enzyme and PheCs biosynthesis, in relation to photosynthetic activity and availability of non-structural carbohydrates (NSC) in spring barley seedlings. High irradiance positively affected A_n, NSC, PheCs content, and antioxidant activity (AOX). High temperature led to decreased A_n, NSC, and increased dark respiration, whilst low temperature was accompanied by reduction of UV-A shielding but increase of PheCs content and AOX. Besides that, irradiance and temperature caused changes in the metabolic profile of PheCs, particularly alteration in homoorientin/isovitexin derivatives ratio, possibly related to demands on AOX-based protection. Moreover, we also observed changes in the ratio of sinapoyl-/feruloyl- acylated flavonoids, the function of which is not yet known. The data also strongly suggested that the NSC content may support the PheCs production.

Impacts of production conditions on goat milk vitamin, carotenoid contents and colour indices

The content, composition and variation of vitamin compounds in goat milk have been little studied. An experimental design was based on 28 commercial farms, selected considering the main feeding system (based on main forage and especially pasture access), goat breed (Alpine vs Saanen) and reproductive management (seasonal reproduction), in the main French goat milk production area. Each farm received two visits (spring and autumn) that included a survey on milk production conditions and bulk milk sampling. Milk vitamins (A, E, B₂, B₆, B₉, B₁₂) and carotenoid concentrations plus colour indices were evaluated. A stepwise approach determined the variables of milk production conditions that significantly altered milk indicators. The main forage in the diet was the major factor altering goat milk vitamin and carotenoid concentrations and colour indices. Bulk milk from goats eating fresh grass as forage was richer in α-tocopherol (+64%), pyridoxal (+35%) and total vitamin B₆ (+31%), and b* index (characterising milk yellowness in the CIELAB colour space) was also higher (+12%) than in milk from goats eating conserved forages. In milk from goats eating fresh grass, concentrations of pyridoxamine, lutein and total carotenoids were higher than in milk of goats fed corn silage (+24, +118 and +101%, respectively), and retinol and α-tocopherol concentrations were higher than in milk of goats fed partially dehydrated grass (+45 and +55%). Vitamin B₂ concentration was higher in milk of goats eating fresh grass than in milk of goats fed hay or corn silage as forage (+10%). However, bulk milk when goats had access to fresh grass was significantly poorer in vitamin B₁₂ than when fed corn silage (-46%) and in γ-tocopherol (-31%) than when fed conserved forage. Alpine goats produced milk with higher vitamin B₂ and folate concentrations than Saanen goats (+18 and +14%, respectively). Additionally, the milk colour index that discriminates milks based on their yellow pigment contents was 7% higher in milk from Alpine than Saanen herds, but milk from Saanen goats was richer in lutein (+46%). Goat milks were richer in vitamins B₂ and B₁₂ and folates, but poorer in vitamin B₆ in autumn than in spring (+12, +133, +15 and -13%, respectively). This work highlights that goat milk vitamin and carotenoid concentrations and colour indices vary mainly according to the main forage of the diet and secondly according to the breed and season.

The roles of photorespiration and alternative electron acceptors in the responses of photosynthesis to elevated temperatures in cowpea

We explored the effects, on photosynthesis in cowpea (Vigna unguiculata) seedlings, of high temperature and light-environmental stresses that often co-occur under field conditions and can have greater impact on photosynthesis than either by itself. We observed contrasting responses in the light and carbon assimilatory reactions, whereby in high temperature, the light reactions were stimulated while CO2 assimilation was substantially reduced. There were two striking observations. Firstly, the primary quinone acceptor (QA ), a measure of the regulatory balance of the light reactions, became more oxidized with increasing temperature, suggesting increased electron sink capacity, despite the reduced CO2 fixation. Secondly, a strong, O2 -dependent inactivation of assimilation capacity, consistent with down-regulation of rubisco under these conditions. The dependence of these effects on CO2 , O2 and light led us to conclude that both photorespiration and an alternative electron acceptor supported increased electron flow, and thus provided photoprotection under these conditions. Further experiments showed that the increased electron flow was maintained by rapid rates of PSII repair, particularly at combined high light and temperature. Overall, the results suggest that photodamage to the light reactions can be avoided under high light and temperatures by increasing electron sink strength, even when assimilation is strongly suppressed.

Photosynthesis: a multiscopic view

A recurring analogy for photosynthesis research is the fable of the blind men and the elephant. Photosynthesis has many complex working parts, which has driven the need to study each of them individually, with an inherent understanding that a more complete picture will require systematic integration of these views. However, unlike the blind men, who are limited to using their hands, researchers have developed over the past decades a repertoire of methods for studying these components, many of which capitalize on unique features intrinsic to each. More recent concerns about food security and clean, renewable energy have increased support for applied photosynthesis research, with the idea of either improving photosynthetic performance as a desired trait in select species or using photosynthetic measurements as a phenotyping tool in breeding efforts or for high precision crop management. In this review, we spotlight the migration of approaches for studying photosynthesis from the laboratory into field environments, highlight some recent advances and speculate on areas where further development would be fruitful, with an eye towards how applied photosynthesis research can have impacts at local and global scales.

Responses of isoprene emission and photochemical efficiency to severe drought combined with prolonged hot weather in hybrid Populus

Isoprene emissions have been considered as a protective response of plants to heat stress, but there is limited information of how prolonged heat spells affect isoprene emission capacity, particularly under the drought conditions that often accompany hot weather. Under combined long-term stresses, presence of isoprene emission could contribute to the maintenance of the precursor pool for rapid synthesis of essential isoprenoids to repair damaged components of leaf photosynthetic apparatus. We studied changes in leaf isoprene emission rate, photosynthetic characteristics, and antioxidant enzyme activities in two hybrid Populus clones, Nanlin 1388 (relatively high drought tolerance) and Nanlin 895 (relatively high thermotolerance) that were subjected to long-term (30 d) soil water stress (25% versus 90% soil field capacity) combined with a natural heat spell (day-time temperatures of 35-40 °C) that affected both control and water-stressed plants. Unexpectedly, isoprene emissions from both the clones were similar and the overall effects of drought on the emission characteristics were initially minor; however, treatment effects and clonal differences increased with time. In particular, the isoprene emission rate only increased slightly in the Nanlin 895 control plants after 15 d of treatment, whereas it decreased by more than 5-fold in all treatment × clone combinations after 30 d. The reduction in isoprene emission rate was associated with a decrease in the pool size of the isoprene precursor dimethylallyl diphosphate in all cases at 30 d after the start of treatment. Net assimilation rate, stomatal conductance, the openness of PSII centers, and the effective quantum yield all decreased, and non-photochemical quenching and catalase activity increased in both control and water-stressed plants. Contrary to the hypothesis of protection of leaf photosynthetic apparatus by isoprene, the data collectively indicated that prolonged stress affected isoprene emissions more strongly than leaf photosynthetic characteristics. This primarily reflected the depletion of isoprene precursor pools under long-term severe stress.

Complex Roles of PsbS and Xanthophylls in the Regulation of Nonphotochemical Quenching in Arabidopsis thaliana under Fluctuating Light

Protection of photosystem II against damage from excess light by nonphotochemical quenching (NPQ) includes responses on a wide range of timescales. The onset of the various phases of NPQ overlap in time making it difficult to discern if they influence each other or involve different photophysical mechanisms. To unravel the complex relationship of the known actors in NPQ, we perform fluorescence lifetime snapshot measurements throughout multiple cycles of alternating 2 min periods of high light and darkness. By comparing the data with an empirically based mathematical model that describes both fast and slow quenching responses, we suggest that the rapidly reversible quenching response depends on the state of the slower response. By studying a series of Arabidopsis thaliana mutants, we find that removing zeaxanthin (Zea) or enhancing PsbS concentration, for example, influences the amplitudes of the slow quenching induction and recovery, but not the timescales. The plants' immediate response to high light appears independent of the illumination history, while PsbS and Zea have distinct roles in both quenching and recovery. We further identify two parameters in our model that predominately influence the recovery amplitude and propose that our approach may prove useful for screening new mutants or overexpressors with enhanced biomass yields under field conditions.

Comprehensive Utilization of Marine Microalgae for Enhanced Co-Production of Multiple Compounds

Marine microalgae are regarded as potential feedstock because of their multiple valuable compounds, including lipids, pigments, carbohydrates, and proteins. Some of these compounds exhibit attractive bioactivities, such as carotenoids, ω-3 polyunsaturated fatty acids, polysaccharides, and peptides. However, the production cost of bioactive compounds is quite high, due to the low contents in marine microalgae. Comprehensive utilization of marine microalgae for multiple compounds production instead of the sole product can be an efficient way to increase the economic feasibility of bioactive compounds production and improve the production efficiency. This paper discusses the metabolic network of marine microalgal compounds, and indicates their interaction in biosynthesis pathways. Furthermore, potential applications of co-production of multiple compounds under various cultivation conditions by shifting metabolic flux are discussed, and cultivation strategies based on environmental and/or nutrient conditions are proposed to improve the co-production. Moreover, biorefinery techniques for the integral use of microalgal biomass are summarized. These techniques include the co-extraction of multiple bioactive compounds from marine microalgae by conventional methods, super/subcritical fluids, and ionic liquids, as well as direct utilization and biochemical or thermochemical conversion of microalgal residues. Overall, this review sheds light on the potential of the comprehensive utilization of marine microalgae for improving bioeconomy in practical industrial application.

Influence of Postharvest Temperatures on Carotenoid Biosynthesis and Phytochemicals in Mature Green Chili (Capsicum annuum L.)

An intense red color appearance in hot chili is what industry commonly demands. The harvested mature green “Takanotsume” chili, a popular cultivar in Japan, incubated at 20 and 30 °C is investigated. At 30 °C, the chili rapidly degraded chlorophylls and obtained an intense red color, but presented an orange–red color at 20 °C. The sample showed higher carotenoid accumulations at 30 °C, along with significantly upregulated carotenoid biosynthesis-related genes—phytoene synthase (Psy), lycopene-β-cyclase (Lcyb), β-carotene hydroxylase (CrtZ), and capsanthin/capsorubin synthase (Ccs)—during the experiment. While the expression of the Ccs gene was reduced, there was a 5.5-fold upregulation of the Psy gene at the end of incubation. At 20 °C, the Psy gene was downregulated. These observations suggest that the expression of individual genes is temperature-dependent, and these would affect specific carotenoid compounds. The antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl; DPPH and ferric-reducing antioxidant power; FRAP) values had no difference between temperatures; the higher content of total phenolics and vitamin C presented in the chili at 30 °C probably corresponds to the advanced ripening process. Thus, 30 °C is the recommended incubation temperature for mature green chili to achieve the industry-demanded intense red color and high accumulation of phytochemicals.

Citrus medica: nutritional, phytochemical composition and health benefits – a review

Health benefits and products ofCitrus medica.

Functional Implications of Photosystem II Crystal Formation in Photosynthetic Membranes

The structural organization of proteins in biological membranes can affect their function. Photosynthetic thylakoid membranes in chloroplasts have the remarkable ability to change their supramolecular organization between disordered and semicrystalline states. Although the change to the semicrystalline state is known to be triggered by abiotic factors, the functional significance of this protein organization has not yet been understood. Taking advantage of an Arabidopsis thaliana fatty acid desaturase mutant (fad5) that constitutively forms semicrystalline arrays, we systematically test the functional implications of protein crystals in photosynthetic membranes. Here, we show that the change into an ordered state facilitates molecular diffusion of photosynthetic components in crowded thylakoid membranes. The increased mobility of small lipophilic molecules like plastoquinone and xanthophylls has implications for diffusion-dependent electron transport and photoprotective energy-dependent quenching. The mobility of the large photosystem II supercomplexes, however, is impaired, leading to retarded repair of damaged proteins. Our results demonstrate that supramolecular changes into more ordered states have differing impacts on photosynthesis that favor either diffusion-dependent electron transport and photoprotection or protein repair processes, thus fine-tuning the photosynthetic energy conversion.

The photoprotective role of spermidine in tomato seedlings under salinity-alkalinity stress

Polyamines are small, ubiquitous, nitrogenous compounds that scavenge reactive oxygen species and stabilize the structure and function of the photosynthetic apparatus in response to abiotic stresses. Molecular details underlying polyamine-mediated photoprotective mechanisms are not completely resolved. This study investigated the role of spermidine (Spd) in the structure and function of the photosynthetic apparatus. Tomato seedlings were subjected to salinity-alkalinity stress with and without foliar application of Spd, and photosynthetic and morphological parameters were analyzed. Leaf dry weight and net photosynthetic rate were reduced by salinity-alkalinity stress. Salinity-alkalinity stress reduced photochemical quenching parameters, including maximum photochemistry efficiency of photosystem II, quantum yield of linear electron flux, and coefficient of photochemical quenching (qP). Salinity-alkalinity stress elevated nonphotochemical quenching parameters, including the de-epoxidation state of the xanthophyll cycle and nonphotochemical quenching (NPQ). Microscopic analysis revealed that salinity-alkalinity stress disrupted the internal lamellar system of granal and stromal thylakoids. Exogenous Spd alleviated the stress-induced reduction of leaf dry weight, net photosynthetic rate, and qP parameters. The NPQ parameters increased by salinity-alkalinity stress were also alleviated by Spd. Seedlings treated with exogenous Spd had higher zeaxanthin (Z) contents than those without Spd under salinity-alkalinity stress. The chloroplast ultrastructure had a more ordered arrangement in seedlings treated with exogenous Spd than in those without Spd under salinity-alkalinity stress. These results indicate that exogenous Spd can alleviate the growth inhibition and thylakoid membrane photodamage caused by salinity-alkalinity stress. The Spd-induced accumulation of Z also may have an important role in stabilizing the photosynthetic apparatus.

Light-harvesting complex B7 shifts the irradiance response of photosynthetic light-harvesting regulation in leaves of Arabidopsis thaliana

The nuclear LHCB7 gene is common in higher plants, encodes a transcript that is well expressed in a subset of leaf mesophyll cells, and is associated with a protein product that is homologous to pigment-binding components of the photosystem (PS) II peripheral antenna complex. We compared the physiological properties of wild type and LHCB7-deficient leaves [DNA insertion, Arabidopsis thaliana (At) ecotype Columbia] in terms of pigment content, CO2 exchange, in vivo transmittance at 810 nm, and chlorophyll fluorescence. The latter two techniques are functional indicators for PSI and PSII, respectively. Key features of the mutant phenotype were confirmed using antisense technology and a hemizygote of two independent AtLHCB7 DNA insertion lines. Growth, leaf pigment composition, white light absorptance, and levels of AtLHCB1-6 were not significantly different in the mutant compared to wild type. Likewise, neither intrinsic PSII light capture efficiency nor partitioning of absorbed radiation to PSII was affected by the mutation. The absence of AtLHCB7 is associated with lower rates of light-saturated photosynthesis and a diminished irradiance threshold for induction of photoprotective non-photochemical quenching. Overall, the pattern of change in light utilization parameters and plastoquinol level indicated that loss of AtLHCB7 expression led to slower Rubisco turnover characterized by pH-dependent balancing of electron transport to reduced carbon assimilation capacity (photosynthetic control). No effect of AtLHCB7 genotype on xanthophyll de-epoxidation state was detected suggesting that factors in addition to lumenal pH influence zeaxanthin accumulation.

A kinetic model of rapidly reversible nonphotochemical quenching

Oxygen-evolving photosynthetic organisms possess nonphotochemical quenching (NPQ) pathways that protect against photo-induced damage. The majority of NPQ in plants is regulated on a rapid timescale by changes in the pH of the thylakoid lumen. In order to quantify the rapidly reversible component of NPQ, called qE, we developed a mathematical model of pH-dependent quenching of chlorophyll excitations in Photosystem II. Our expression for qE depends on the protonation of PsbS and the deepoxidation of violaxanthin by violaxanthin deepoxidase. The model is able to simulate the kinetics of qE at low and high light intensities. The simulations suggest that the pH of the lumen, which activates qE, is not itself affected by qE. Our model provides a framework for testing hypothesized qE mechanisms and for assessing the role of qE in improving plant fitness in variable light intensity.