Photo-protection and photo-inhibition during light induction in Barbula indica and Conocephalum conicum under different light gradients

The objectives of this study were to measure the chlorophyll fluorescence (ChlF) parameters of Barbula indica (Hook.) Spreng and Conocephalum conicum (L.) Dumort subjected to various light intensities (LI) as a reflection of their adaptability to their habitats. The electron transport rate (ETR) of all plants under 500 μmol m-2 s-1 photosynthetic photon flux density (PPFD) was significantly higher than other LI treatments, implying that these plants could be grown under a specific and optimal light intensity adapted to 500 PPFD conditions. As LI increased from 50 to 2,000 PPFD, we observed in all plants increased non-photochemical quenching (NPQ) and photo-inhibitory quenching (qI) and decreased photosystem II efficiency (ΦPSII), potential quantum efficiency of PSII (Fv/Fm), actual PSII efficiency (ΔF/Fm'%), and Fv/Fm%. In addition, energy-dependent quenching (qE), the light protection system (qE + qZ + qT), and qI increased as ΦPSII decreased and photo-inhibition% increased under 1000, 1500, and 2000 PPFD conditions, suggesting that these plants had higher photo-protective ability under high LI treatments to maintain higher photosynthetic system performance. B. indica plants remained photochemically active and maintained higher qE under 300, 500, and 1000 PPFD, whereas C. conicum qZ + qT exhibited higher photo-protection under 500, 1000, and 1500 PPFD conditions. These ChlF indices can be used for predicting photosynthetic responses to light induction in different bryophytes and provide a theoretical basis for ecological monitoring.

Evaluating β-cryptoxanthin antioxidant properties against ROS-induced macromolecular damages and determining its photo-stability and in-vitro SPF

Natural antioxidants have become vital to minimize macromolecular damage caused by Reactive Oxygen Species (ROS). This study investigated the antioxidant property of β-cryptoxanthin (β-CRX) extracted from Kocuria marina DAGII and its protective effect against macromolecular damages by generating ROS via two models: UV radiation and the Fenton reaction. β-cryptoxanthin exhibited the highest scavenging activity towards hydrogen peroxide radicals with an IC50 value of 38.30 ± 1.13 μg/ml, favoring the hydrogen atom transfer mechanism. The total antioxidant capacity value of 872.0101 ± 1.84 μg BHT/mg β-CRX indicated the cumulative ROS scavenging ability of β-cryptoxanthin. β-cryptoxanthin could protect against ROS-induced lipid peroxidation, protein oxidation, and DNA damage. The highest lipid peroxidation and protein oxidation inhibition values of β-cryptoxanthin against ROS were 99.371 ± 0.51% and 78.19 ± 0.15%, respectively. β-cryptoxanthin also showed a protective effect in maintaining DNA intactness against ROS-mediated DNA damage. Allium cepa test showed the non-genotoxic nature of β-cryptoxanthin and its protective effect against ROS genotoxic effects. A photo-stability study of β-cryptoxanthin toward UVA and UVB radiation showed a rapid bleaching result of UVB obeying pseudo-zero order kinetics with an average R2 value of 0.9897 and a higher k value (-6.3 × 10-11 ± 0.2 M/s) than UVA (k value -3.1 × 10-11 ± 0.17 M/s), signifying that UVB is more potent toward photo-degradation. The good SPF value of 23.1737 ± 0.15 showed the UV protection capability of β-cryptoxanthin. Thus, the present study suggests that β-cryptoxanthin could be a valuable antioxidant to protect against ROS-induced various macromolecular damages and act as a good UV protectant.

UVB light influence on the laccase enzyme catalytic activity in reverse micelles and in homogeneous aqueous medium

Laccase is a versatile enzyme widely used for the oxidation of environmental contaminants and exhibits great potential in many others applications; however, it undergoes photo-degradation when irradiated with UVB light. The photo-stability of this biomolecule can be improved by immobilization in different encapsulation media and reverse micelles have been employed with this purpose. The laccase activity using syringaldazine as substrate has been studied in the absence and in the presence of reverse micelles of 0.15 M of sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT) in isooctane at W₀ ([H₂O]/[AOT]) = 30, before and after irradiation of the enzyme with UVB light. The kinetic parameters, i.e., Michaelis-Menten constant (K_M), catalytic constant (k_CAT), and catalytic efficiency (k_CAT/K_M), were determined by spectroscopic measurements in the micellar system and in homogeneous aqueous medium. The distribution of the substrate in two pseudo-phases (micelle and organic solvent) was taking into account in the kinetic parameters' determinations. The results obtained indicate that the nano-aggregate system confers a solubilization media in the water core of the micelle, both for the enzyme and the substrate, in which the catalytic function of the enzyme is preserved. On the other hand, in homogeneous aqueous medium k_CAT/K_M value, it is reduced by ~50% after UVB irradiation of the enzyme, while in micellar medium, less than 10% of the activity was affected. This mean that the enzyme achieves a considerably photo-protection when it is irradiated with UVB light in reverse micelles as compared with the homogeneous aqueous medium. This phenomenon can be mainly due to the confinement of the biomolecule inside the micelle. Physical properties of the nano-environment could affect photochemical reactions.

Enhanced Streptomyces roseochromogenes melanin production by using the marine renewable source Posidonia oceanica egagropili

Since the possibility to biotechnologically produce melanin by Streptomycetes using plant biomass has been so far poorly investigated, Posidonia oceanica egagropili, a marine waste accumulating along the Mediterranean Sea coasts, was explored as a renewable source to enhance extracellular melanin production by Streptomyces roseochromogenes ATCC 13400. Therefore, different amounts of egagropili powder were added to a culture medium containing glucose, malt extract, and yeast extract, and their effect on the melanin biosynthesis was evaluated. A 2.5 g·L^-1 supplementation in 120-h shake flask growths at 26 °C, at pH 6.0 and 250 rpm, was found to enhance the melanin production up to 3.94 ± 0.12 g·L^-1, a value 7.4-fold higher than the control. Moreover, 2-L batches allowed to reach a concentration of 9.20 ± 0.12 g·L^-1 in 96 h with a productivity of 0.098 g·L^-1·h^-1. Further studies also demonstrated that the melanin production enhancement was due to the synergistic effect of both the lignin carbohydrate complex and the holocellulose components of the egagropili. Finally, the pigment was purified from the broth supernatant by acidic precipitation and reversed-phase chromatography, characterized by UV absorbance and one- and two-dimensional NMR, and also tested for its chemical, antioxidant, and photo-protective properties. KEY POINTS: • S. roseochromogenes ATCC 13400 produces extracellular soluble melanin. • Egagropili added to the growth medium enhances melanin production and productivity. • Both the lignin carbohydrate complex and the holocellulose egagropili components influence the melanin biosynthesis.

Diverse chemical modifications of the chlorogenic acid composition of Viscum combreticola Engl.: A premise for the state of readiness against excessive sunlight exposure

Mistletoe plants that are positioned on the canopy of their hosts are more susceptible to UV radiation exposure. These aerial plants are resistant to damage by UV radiation due the presence of epidermal constituents such as the cuticle, cork layer, trichomes and antioxidant secondary metabolites. In response to the photo-oxidative stress associated with UV exposure, plants generally deploy photo-protective responsive mechanisms that involve the biosynthesis of UV absorbing phenolic compounds such as chlorogenic acids (CGAs). The hydroxycinnamic acid moieties of these CGAs are predominantly in the trans configuration, naturally. However, excessive sunlight exposure of plants containing these compounds can result in geometrical isomerisation, characterized by the formation of cis isomers. Therefore, in this study, the effect of UV light radiation on the CGA composition of Viscum combreticola Engl. (Santalacaeae) plants using an in vitro model was unravelled through UHPLC-q-TOF-MS-based metabolic profiling. Interestingly, the findings of this study revealed that this plant has a diverse chemical composition of CGAs that is characterized by epimerization, monoacylation, homodiacylation and heterodiacylation of the quinic acid (QA), thereby, contributing to the state of readiness in these plants against sunlight or UV exposure. In addition to the commonly reported cinnamoyl containing heterodiacylated CGAs, hydroxybenzoyl containing heterodiacylated CGAs were also reported in this study. Moreover, cis isomers (24 in total) of some CGAs were identified in the non-irradiated samples and the formation of these compounds has been reported to help plants in the mitigation of photo-oxidative stress. An additional 28 cis isomers of CGAs and HCA derivatives were observed in the UV-irradiated samples, hence, further increasing the complexity of the metabolome of this plant, with a total of 108 compounds identified in this study. The presence of epimers, positional and geometrical isomers of these compounds could be a biochemical strategy to maximize the chemical arsenal of this plant to withstand the photo-oxidative stress posed by UV radiation from the sunlight. Due to purported pharmacological properties associated with the identified compounds these parasitic plants can be a rich source of prospective therapeutic compounds that can be employed as drug discovery leads. Moreover, UV radiation might be essential in future to produce potent drugs since plants naturally produce these compounds in low quantities.

High throughput procedure utilising chlorophyll fluorescence imaging to phenotype dynamic photosynthesis and photoprotection in leaves under controlled gaseous conditions

BACKGROUND

As yields of major crops such as wheat (T. aestivum) have begun to plateau in recent years, there is growing pressure to efficiently phenotype large populations for traits associated with genetic advancement in yield. Photosynthesis encompasses a range of steady state and dynamic traits that are key targets for raising Radiation Use Efficiency (RUE), biomass production and grain yield in crops. Traditional methodologies to assess the full range of responses of photosynthesis, such a leaf gas exchange, are slow and limited to one leaf (or part of a leaf) per instrument. Due to constraints imposed by time, equipment and plant size, photosynthetic data is often collected at one or two phenological stages and in response to limited environmental conditions.

RESULTS

Here we describe a high throughput procedure utilising chlorophyll fluorescence imaging to phenotype dynamic photosynthesis and photoprotection in excised leaves under controlled gaseous conditions. When measured throughout the day, no significant differences (P > 0.081) were observed between the responses of excised and intact leaves. Using excised leaves, the response of three cultivars of T. aestivum to a user-defined dynamic lighting regime was examined. Cultivar specific differences were observed for maximum PSII efficiency (F v'/F m'-P < 0.01) and PSII operating efficiency (F q'/F m'-P = 0.04) under both low and high light. In addition, the rate of induction and relaxation of non-photochemical quenching (NPQ) was also cultivar specific. A specialised imaging chamber was designed and built in-house to maintain gaseous conditions around excised leaf sections. The purpose of this is to manipulate electron sinks such as photorespiration. The stability of carbon dioxide (CO2) and oxygen (O2) was monitored inside the chambers and found to be within ± 4.5% and ± 1% of the mean respectively. To test the chamber, T. aestivum 'Pavon76' leaf sections were measured under at 20 and 200 mmol mol-1 O2 and ambient [CO2] during a light response curve. The F v'/F m'was significantly higher (P < 0.05) under low [O2] for the majority of light intensities while values of NPQ and the proportion of open PSII reaction centers (qP) were significantly lower under > 130 μmol m-2 s-1 photosynthetic photon flux density (PPFD).

CONCLUSIONS

Here we demonstrate the development of a high-throughput (> 500 samples day-1) method for phenotyping photosynthetic and photo-protective parameters in a dynamic light environment. The technique exploits chlorophyll fluorescence imaging in a specifically designed chamber, enabling controlled gaseous environment around leaf sections. In addition, we have demonstrated that leaf sections do not different from intact plant material even > 3 h after sampling, thus enabling transportation of material of interest from the field to this laboratory based platform. The methodologies described here allow rapid, custom screening of field material for variation in photosynthetic processes.

Photo-protective compounds in red macroalgae from Brittany: Considerable diversity in mycosporine-like amino acids (MAAs)

To cope with the biotic and abiotic stresses experienced within their environment, marine macroalgae have developed certain defence mechanisms including the synthesis of photo-protective molecules against light and particularly harmful UV radiation. The aim of this study was to screen selected red algae, a highly diverse phylogenetic group, for the production of photo-protective molecules. The pigment content and composition (i.e. chlorophyll-a, phycobiliproteins and carotenoids) and the composition of mycosporine-like amino acids (MAAs) were studied in 40 species of red macroalgae collected in Brittany (France), at two distinct periods (i.e. February and July 2017). A high inter-specific variability was demonstrated in terms of pigment content and MAA composition. Twenty-three potential MAAs were detected by HPLC, and six were identified by LC-MS (i.e. shinorine, palythine, asterina-330, porphyra-334, usurijene and palythene). This is the first study to report on the composition of pigments and MAAs in a diverse group of red seaweeds from Brittany, including some species for which the MAA composition has never been studied before. Nevertheless, the results suggested that some species of red algae are more likely to cope with high levels of light radiation since those species such as Bostrychia scorpioides, Porphyra dioica, Gracilaria vermiculophylla and Vertebrata lanosa are living in environments exposed to higher levels of irradiation, and had various MAAs in addition to their photo-protective pigments.

Photo-protective mechanisms in reed canary grass to alleviate photo-inhibition of PSII on the Qinghai-Tibet Plateau

Due to its characteristic of high biomass yield potential, there is considerable interest in cultivating Phalaris arundinacea L. cv. 'chuancaoyin No.3' (reed canary grass) on the Qinghai-Tibet Plateau where there is an abundance of alpine steppe meadow and a potential large market for animal husbandry. In this study, we 1) investigate whether reed canary grass exhibits superior productive capacity to Elymus nutans 'Aba' (E. nutans), ordinary common pasture, during the long warm days of summer at high-altitude; and 2) compare the cold tolerance between reed canary grass and E. nutans, including photosynthesis, photo-inhibition, and photo-protection. The results suggest that reed canary grass exhibits higher photosynthetic capacity compared to E. nutans at latitudes of the cool temperate zone. Meanwhile, cold-induced photo-inhibition and photo-damage at high altitudes in reed canary grass were due to both stomatal and non-stomatal limitation, and the enhancement in photo-respiration, thermal dissipation, and Mehler reaction are important processes to minimize the negative effects of high elevation and a cold environment.

Metabolomics analysis reveals the metabolic and functional roles of flavonoids in light-sensitive tea leaves

BACKGROUND

As the predominant secondary metabolic pathway in tea plants, flavonoid biosynthesis increases with increasing temperature and illumination. However, the concentration of most flavonoids decreases greatly in light-sensitive tea leaves when they are exposed to light, which further improves tea quality. To reveal the metabolism and potential functions of flavonoids in tea leaves, a natural light-sensitive tea mutant (Huangjinya) cultivated under different light conditions was subjected to metabolomics analysis.

RESULTS

The results showed that chlorotic tea leaves accumulated large amounts of flavonoids with ortho-dihydroxylated B-rings (e.g., catechin gallate, quercetin and its glycosides etc.), whereas total flavonoids (e.g., myricetrin glycoside, epigallocatechin gallate etc.) were considerably reduced, suggesting that the flavonoid components generated from different metabolic branches played different roles in tea leaves. Furthermore, the intracellular localization of flavonoids and the expression pattern of genes involved in secondary metabolic pathways indicate a potential photoprotective function of dihydroxylated flavonoids in light-sensitive tea leaves.

CONCLUSIONS

Our results suggest that reactive oxygen species (ROS) scavenging and the antioxidation effects of flavonoids help chlorotic tea plants survive under high light stress, providing new evidence to clarify the functional roles of flavonoids, which accumulate to high levels in tea plants. Moreover, flavonoids with ortho-dihydroxylated B-rings played a greater role in photo-protection to improve the acclimatization of tea plants.

Acclimation strategy of Rhodopseudomonas palustris to high light irradiance

The ability of Rhodopseudomonas palustris cells to rapidly acclimate to high light irradiance is an essential issue when cells are grown under sunlight. The aim of this study was to investigate the photo-acclimation process in Rhodopseudomonas palustris 42OL under different culturing conditions: (i) anaerobic (AnG), (ii) aerobic (AG), and (iii) under H₂-producing (HP) conditions both at low (LL) and high light (HL) irradiances. The results obtained clearly showed that the photosynthetic unit was significantly affected by the light irradiance at which Rp. palustris 42OL was grown. The synthesis of carotenoids was affected by both illumination and culturing conditions. At LL, lycopene was the main carotenoid synthetized under all conditions tested, while at HL under HP conditions, it resulted the predominant carotenoid. Oppositely, under AnG and AG at HL, rhodovibrin was the major carotenoid detected. The increase in light intensity produced a deeper variation in light-harvesting complexes (LHC) ratio. These findings are important for understanding the ecological distribution of PNSB in natural environments, mostly characterized by high light intensities, and for its growth outdoors.

Evidence for the role of cyclic electron flow in photoprotection for oxygen-evolving complex

Cyclic electron flow (CEF) alleviates PSII photo-inhibition under high light by at least two different mechanisms: one is liked to thermal energy dissipation (qE) and the other one is independent of qE. However, the latter mechanism is unclear. Because the photodamage to PSII primarily occurred at the oxygen-evolving complex (OEC), and the stability of OEC is dependent on proton gradient across thylakoid membrane (ΔpH), we hypothesize that the CEF-dependent generation of ΔpH can alleviate photodamage to OEC. To test this hypothesis, we determined the effects of antimycin A (AA), methyl viologen (MV), chloramphenicol (CM), nigericin (Nig) on PSII activity and the stability of OEC for leaves of a light-demanding tropical tree species Erythrophleum guineense by the analysis of OKJIP chlorophyll a fluorescence transient. After high light treatment, the stronger decrease in Fv/Fm in the AA-, CM-, MV-, and Nig-treated samples was accompanied with larger photo damage of OEC. The AA-treated samples significantly showed lower CEF activity than the H2O-treated samples. Although the AA-treated leaves significantly showed stronger PSII photo-inhibition and photo-damage of OEC compared to the H2O-treated leaves, the value of non-photochemical quenching did not differ between them. Therefore, CEF activity was partly inhibited in the AA-treated samples, and the stronger PSII photo-inhibition in the AA-treated leaves was independent of qE. Taking together, we propose a hypothesis that CEF-dependent generation of ΔpH under high light plays an important role in photoprotection for the OEC activity.

Effective protection of biological membranes against photo-oxidative damage: Polymeric antioxidant forming a protecting shield over the membrane

We have prepared a chitosan polymer modified with gallic acid in order to develop an efficient protection strategy biological membranes against photodamage. Lipid bilayers were challenged with photoinduced damage by photosensitization with methylene blue, which usually causes formation of hydroperoxides, increasing area per lipid, and afterwards allowing leakage of internal materials. The damage was delayed by a solution of gallic acid in a concentration dependent manner, but further suppressed by the polymer at very low concentrations. The membrane of giant unilamellar vesicles was covered with this modified macromolecule leading to a powerful shield against singlet oxygen and thus effectively protecting the lipid membrane from oxidative stress. The results have proven the discovery of a promising strategy for photo protection of biological membranes.

Biomass and carotenoid production in photosynthetic bacteria wastewater treatment: effects of light intensity

This study investigated the feasibility of using photosynthetic bacteria (PSB) to produce biomass and carotenoid while treating wastewater. The effects of light intensity on the biomass, carotenoid and bacteriochlorophyll accumulation in together with pollutant removal were studied. Results showed that it was feasible to use PSB to treat wastewater as well as to produce biomass or carotenoid. 2000 lux was an optimal intensity for biomass production and COD removal, and the corresponding values were 2645 mg/L and 94.7%. 8000 lux was an optimal light intensity for carotenoid production (1.455 mg/L). Mechanism analysis displayed that the greater the bacteriochlorophyll and carotenoid were secreted, the lower the light conversion efficiency turned out to be. The highest light conversion efficiency was achieved at 500 lux; the ATP production, biomass production, and COD removal were the highest at 2000 lux, but the bacteriochlorophyll and carotenoid content were the lowest at 2000 lux.

Photochemical and photophysical properties of carotenoid immobilized on a surfactant micellar medium including chlorophyll as an artificial photosynthesis system

To develop an artificial photosynthesis model, the anionic water-soluble carotenoid dye crocetin was electrostatically immobilized onto the surface of cationic surfactant cetyltrimethylammonium bromide (CTAB) micellar medium including Mg chlorophyll-a and b (MgChl-a and b) (Cro/MgChl), and its photophysical properties were studied using UV-vis absorption and fluorescence spectroscopy. The fluorescence of MgChl-a and b was observed, with the excitation wavelength attributed to the absorption band of crocetin, indicating that photo-induced energy transfer from the photoexcited state of crocetin to MgChl-a and b occurs. The photostability of MgChl-a and b in Cro/MgChl was investigated under continuous irradiation. After 60 min irradiation, the absorbance decreases at 660 nm Cro/MgChl and MgChl-a/b, without crocetin, were 3.0 and 17%, respectively. These results indicate that the photo-bleaching rate of MgChl-a/b in Cro/MgChl on irradiation is suppressed by the crocetin molecule on the surface of micelles.