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Skin cancer is the most common human malignancy worldwide and solar ultraviolet (UV) radiation is known to serve an important role in its pathogenesis. Natural candidate compounds with antioxidant, photoprotective and anti-melanogenic effects were investigated against the background of skin photoprotective and anti-melanogenic properties. Gomisin D, J and O are dibenzocyclooctadiene lignans present in Kadsura medicinal plants and possess several pharmacological activities. In this study, the functions and mechanisms underlying the effects of gomisin D, J and O in UVA-and UVB-irradiated keratinocytes and α-melanocyte stimulating hormone (α-MSH)-stimulated melanocytes were explored. Following UVA and UVB irradiation, keratinocytes were treated with gomisin D, J and O, and keratinocyte viability, lactate dehydrogenase (LDH) release, intracellular reactive oxygen species (ROS) production and apoptosis were examined. The results demonstrated that gomisin D and J improved keratinocyte viability and reduced LDH release under UVA and UVB irradiation. Intracellular ROS production induced by UVA and UVB irradiation was suppressed by gomisin D and J. In addition, Annexin V and TUNEL staining analysis indicated that gomisin D and J have significant anti-apoptotic effects on UVA-and UVB-irradiated keratinocytes. After α-MSH stimulation, melanocytes were treated with gomisin D, J and O, and the changes in melanocyte viability, intracellular melanin content, intracellular tyrosinase activity, and mechanisms underlying these changes were examined. Gomisin D markedly inhibited the α-MSH-induced increase in intracellular melanin content and tyrosinase activity. Mechanistically, gomisin D reduced the protein and mRNA expression levels of microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein (TRP)-1 and TRP-2 in α-MSH-stimulated melanocytes. In addition, gomisin D markedly downregulated α-MSH-induced phosphorylation of protein kinase A and cAMP response element binding protein, which are known to be present upstream of the MITF, tyrosinase, TRP-1 and TRP-2 genes. Overall, gomisin D has photoprotective and anti-melanogenic effects; these findings provide a basis for the production of potential brightening and photoprotective agents using natural compounds such as gomisin D.

Photochemoprevention can be a valuable approach to counteract the damaging effects of environmental stressors (e.g., UV radiations) on the skin. Pigments are bioactive molecules, greatly attractive for biotechnological purposes, and with promising applications for human health. In this context, marine microalgae are a valuable alternative and eco-sustainable source of pigments that still need to be taken advantage of. In this study, a comparative in vitro photochemopreventive effects of twenty marine pigments on carcinogenic melanoma model cell B16F0 from UV-induced injury was setup. Pigment modulation of the intracellular reactive oxygen species (ROS) concentration and extracellular release of nitric oxide (NO) was investigated. At the cell signaling level, interleukin 1-β (IL-1β) and matrix metallopeptidase 9 protein (MMP-9) protein expression was examined. These processes are known to be involved in the signaling pathway, from UV stress to cancer induction. Diatoxanthin resulted the best performing pigment in lowering MMP-9 levels and was able to strongly lower IL-1β. This study highlights the pronounced bioactivity of the exclusively aquatic carotenoid diatoxanthin, among the others. It is suggested increasing research efforts on this molecule, emphasizing that a deeper integration of plant ecophysiological studies into a biotechnological context could improve the exploration and exploitation of bioactive natural products.

The formation, characterization, photo-protective properties and release profiles of folic acid-loaded nanolaminated films were investigated by UV-visible spectroscopy, FTIR, Raman and SEM microscopy. Food-grade alginate/chitosan nanolaminates were obtained by the layer-by-layer technique and folic acid (FA) was incorporated by post-diffusion. The FA concentration of loading solutions and immersion time significantly affected the FA content in nanolaminates. The maximum FA loading was reached using FA solutions at 10 mg/mL for 30 min (54.4 μg/cm2), or 12.5 mg/mL for 120 min (≈70 μg/cm2). Nanolaminates containing FA were more stable under ultraviolet light exposure than non-encapsulated FA. The rate and concentration of FA released from nanolaminates were greater at buffer pH 7 than at pH 3, which might play a key role in the delivery and bioavailability of nutraceuticals. These results provide important information for the design of nanolaminates containing hydrophilic active compounds for food applications. This research was supported by the Ministerio de Ciencia e Innovación throughout the projects AGL2009-11475 and MINECO ALG2012-35635. Author Acevedo-Fani also thanks to the University of Lleida for the pre-doctoral grant.

Diospyros kaki L.f. belonging to family Ebenaceae, commonly known as persimmon is used as a medicinal plant in Chinese traditional medicine since many years for different ailments including cosmetics and dermatologic applications. Traditionally this plant is used to treat different skin conditions including pimples, skin eruptions and eczema. Present interest has been focused toward use of natural bioactive compounds in various curative and beautifying applications in dermatological and cosmeceutical disciplines. The objective of this article is to present cumulative data on potential use of D. kaki for its possible role in dermatologic and cosmetic applications. Scientific data has revealed an excellent position of D. kaki in both dermatology and cosmetic discipline making it a valuable choice in respective field. Active principles from different plant parts have shown to possess anti-inflammatory, antiallergic, photo-protective, and anti-wrinkle effects with appreciable activities against tyrosinase, elastase, and collagenase enzymes. Promising antioxidant activity and skin whitening potential, augmented by reduction in sebum contents, and reduction in size and number of skin pores make it a suitable choice as cosmetic ingredient. Data has been summarized and presented on available molecular mechanism that can contribute toward phytoconstituents usage in cosmetics and dermatology mediated by different cellular pathways. Crude extracts and some of phytochemical obtained from this plant such as isoquercitrin and hyperin have better reported activities than well-known cosmetic ingredients viz., arbutin, kojic acid and hydroquinone with possibility of having no side effects. Photo protection against degenerative effects of UVA, UVB and gamma radiation can help skin to fight well against oxidative stress and reactive oxygen species. Further investigation need to be directed toward human subjects for evaluation of these reported activities for obtaining optimum commercial and industrial benefits from this valuable plant. Keywords: Persimmon, Anti-tyrosinase, Anti-wrinkle, Photo-protection, Cosmetics, Antioxidant

WOS:000520805600001; Changes in pigment (chlorophyll-a, carotenoids and phycobiliproteins) and mycosporine-like amino acid (MAA) composition were studied in the red edible macroalga Palmaria palmata, harvested between February 2018 and February 2019 at 2 sites from Brittany (France). The results occuring in natural conditions revealed a high seasonal variability that can be related to a combination of environmental parameters, including light, nutrients, temperature, salinity and pH, which may have synergistic or antagonistic effects. A decrease in pigments was observed in summer, matching with the increase in irradiance at the same period. On the contrary, the increase in light from February to May has caused an increase in the total MAA content, confirming the UV-photoprotective role attributed to these compounds. Analysis of the results coupled with the biosynthesis pathway suggests that some MAAs are favoured in the occurrence of high irradiance. In this sense, asterina-330 was synthetized only between March and July and not the rest of the year, supporting its importance in photoprotection. In addition, analysis revealed that nutrient availibility could have a significant influence on MAAs since their synthesis seemed to be limited in summer, despite significant exposure to light. However, this decrease could be due to another potential role of MAAs as a nitrogen source for macroalgae. Thus, the diversity of these compounds and the different synthesis pathways could be explained by different roles including photo-protection and nitrogen source, making MAA multi-purpose protective agents which could play a key role in the adaptation of this species to its changing environment.

Modern lifestyles have developed new attention on appearance and personal care which attract a huge number of consumers towards cosmetic products. The demand for a skincare product with natural ingredients is rapidly increasing. Seaweeds are major resources for in-demand active compounds with a wide variety of applications. The use of seaweed-derived ingredients in cosmetic products has increased in recent years as many scientific studies have proved the potential skincare properties of seaweed bioactive compounds. This review emphasizes possible skincare properties of seaweed bioactive compounds. The review outlines the mechanism involved in skin problems including hyperpigmentation, premature skin aging, and acne in the first part while the second part focuses on the promising application of seaweeds in skin protection by highlighting the bioactive compound responsible for their bioactivity.

BackgroundAs 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.ResultsHere 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 ofT. aestivumto a user—defined dynamic lighting regime was examined. Cultivar specific differences were observed for maximum PSII efficiency (Fv′/Fm′—P Fq′/Fm′—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−1O2and ambient [CO2] during a light response curve. TheFv′/Fm′was significantly higher (P 2] 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−2s−1photosynthetic photon flux density (PPFD).ConclusionsHere 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.

Excessive exposure to ultraviolet (UV) radiation is the main risk factor to develop skin pathologies or cancer because it encourages oxidative condition and skin inflammation. In this sense, strategies for its prevention are currently being evaluated. Natural products such as carotenoids or polyphenols, which are abundant in the marine environment, have been used in the prevention of oxidative stress due to their demonstrated antioxidant activities. Nevertheless, the anti-inflammatory activity and its implication in photo-prevention have not been extensively studied. Thus, we aimed to evaluate the combination of fucoxanthin (FX) and rosmarinic acid (RA) on cell viability, apoptosis induction, inflammasome regulation, and anti-oxidative response activation in UVB-irradiated HaCaT keratinocytes. We demonstrated for the first time that the combination of FX and RA (5 &micro, M RA plus 5 &mu, M FX, designated as M2) improved antioxidant and anti-inflammatory profiles in comparison to compounds assayed individually, by reducing UVB-induced apoptosis and the consequent ROS production. Furthermore, the M2 combination modulated the inflammatory response through down-regulation of inflammasome components such as NLRP3, ASC, and Caspase-1, and the interleukin (IL)-1&beta, production. In addition, Nrf2 and HO-1 antioxidant genes expression increased in UVB-exposed HaCaT cells pre-treated with M2. These results suggest that this combination of natural products exerts photo-protective effects by down-regulating NRLP3-inflammasome and increasing Nrf2 signalling pathway.

International audience; 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 (Le. 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.

Topical sun protective cosmetics (sunscreens, pre- and post-sun) have been intensively developed and produced to protect human skin against solar irradiation-associated damages/pathologies. Unfortunately, routine cosmetics for sun protection containing synthetic organic and/or physical sunscreens could exert adverse effects towards human organisms and bring undesirable ecological changes. Terrestrial and marine plant species, being exposed to sun light for hundreds of millions of years, have evolved two pro-survival strategies: effective protection against/adaptation to its deleterious effects and the use of solar energy for photosynthesis/photo-biochemical reactions. Secondary plant metabolites (SPM) are primary sensors of solar energy and mediators of its use (photo-sensitisers) or neutralisation (photo-protectors). A similar double photo-protective/photo-sensitising system is built in within human skin. Modern development of toxicologically/ecologically safe yet effective sun-protective cosmetics attempts to pre-select photo-stable and non-phototoxic SPMs that provide broad UVA + UVB sunscreen, free radical scavenging and direct antioxidant defence, endogenous antioxidant rescue, induction of antioxidant enzymes (indirect antioxidant defence), and normalisation of metabolic and immune responses to UVA + UVB. Proper formulation of sun protective cosmetics should assure targeted delivery of photo-active SPMs to definite skin layers to invigorate the built in photo-chemical skin barrier.

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.

Age-related macular degeneration (AMD) is a degenerative retinal disease that causes blindness in people 60-65 years and older, with the highest prevalence appearing in people 90 years-old or more. Epidemiological estimates indicate that the number of cases is increasing, and will almost double in the next 20 years. Preventive measures require precise etiological knowledge. This is quite difficult, since AMD is a multifactorial condition with intricate relationships between causes and risk factors. In this review, we describe the impact of light on the structure and physiology of the retina and the pigment epithelium, taking into account the continuous exposure to natural and artificial light sources along the life of an individual. A large body of experimental evidence demonstrates the toxic effects of some lighting conditions on the retina and the pigment epithelium, and consensus exists about the importance of photo-oxidation phenomena in the causality chain between light and retinal damage. Here, we analyzed the transmission of light to the retina, and compared the aging human macula in healthy and diseased retinas, as shown by histology and non-invasive imaging systems. Finally, we have compared the putative retinal photo-sensitive molecular structures that might be involved in the genesis of AMD. The relationship between these compounds and retinal damage supports the hypothesis of light as an important initiating cause of AMD. Fil: Marquioni Ramella, Melisa Daniela. Universidad Austral. Facultad de Ciencias Biomédicas. Laboratorio de Investigaciones Biomédicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Suburo, Angela Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Austral. Facultad de Ciencias Biomédicas. Laboratorio de Investigaciones Biomédicas; Argentina

The plant Calendula officinalis L. is widely applied due to its medicinal properties, which are mainly dermatological and ornamental. The goal of this study is to assess the phytochemical components in a hydroethanolic extract (HECO) from the leaves of Calendula officinalis L. using UV-VIS spectrophotometry and thin layer chromatography (TLC), as well as to identify and quantify the components related to its antioxidant capacity employing high performance liquid chromatographic (HPLC). The antioxidant capacity evaluation was performed using the DPPH method for superoxide and hydroxyl radicals. The photo-protective capacity was evaluated by UVspectrophotometry in order to determine the in vitro Sun Protection Factor(SPF). The results show the plant’s strong antioxidant activity (DPPH and hydroxyl methods), which we believe to be related to the presence of flavonoids (24.67 mg/g), polyphenols (33.90 mg/g), condensed tannins (27.30 mg/g), and the amount of rutin (37.25 mg/g), and quercetin (6.09 mg/g) found during the study. The HECO presented a good antioxidant capacity, most likely due to the polyphenols, flavonoids, and tannins in its contents. However, the obtained SPF of 1.89 ± 0.05 does not allow the plant to be classified as a stand-alone sunscreen, and more studies are needed in order to test its ability to enhance sunscreens in existing cosmetic formulations. RESUMO A Calendula officinalis L. é uma planta amplamente utilizada por suas propriedades medicinais, principalmente dermatológica e ornamental. O objetivo deste estudo é avaliar constituintes fitoquímicos do extrato hidroetanólico das folhas de Calêndula officinalis L. (HECO) por espectrofotometria UV-visível e cromatografia em camada delgada (CCD), bem como detectar e quantificar os componentes relacionados com a capacidade antioxidante por Cromatografia Líquida de Alta Eficiência (CLAE). Posteriormente, foi avaliada a capacidade antioxidante pelo método do DPPH, radicais superóxido e hidroxila. Além disso, a capacidade fotoprotetora foi avaliada através de espectrofotometria UV para determinação do Fator de Proteção Solar in vitro (FPS). Os resultados evidenciaram que a planta apresentou uma excelente atividade antioxidante para o método do DPPH e do radical hidroxila, o que pode estar relacionada com a presença de flavonoides (24,67 mg/g), polifenóis (33,90 mg/g) e taninos condensados (27,30 mg/g) e da quantidade de rutina (37,25 mg/g) e quercetina (6,09 mg/g) encontrados neste estudo. O HECO apresentou uma notável capacidade antioxidante, provavelmente devido à presença de polifenóis, flavonoides e taninos. O valor do FPS encontrado (1,89 ± 0,05), não classifica a planta como um protetor solar isolado. No entanto, mais estudos são necessários para testar a capacidade de potencializar filtros solares em formulações cosméticas.

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. Electronic supplementary material The online version of this article (doi:10.1186/s12870-017-1012-8) contains supplementary material, which is available to authorized users.

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.

International audience; Low-temperature crystalline deposition techniques are important, especially for coating polymer films that cannot tolerate high temperatures. In this work, crystalline anatase titanium dioxide (TiO2) thin films were deposited by reactive radio-frequency (RF) magnetron sputtering on unheated poly(ethylene terephthalate) (PET) films. The stability of the polymer film under UV-light irradiation in air was then studied. With only a TiO2 layer the polymer film was degraded by in-air, UV radiation. However, a transparent bilayer coating, consisting of a TiO2 layer on top of an ultra-thin sputtered alumina (Al2O3) layer, on the PET film effectively protected the polymer layer from photo-oxidation. Furthermore, the top anatase TiO2 layer has very good photo-catalytic activity, as shown by its ability to photo-degrade rhodamine B dye solution. The combination of these two properties allows photo-stable and transparent polymer/ceramic layered media with a self-cleaning surface.

Plants are particularly prone to photo-oxidative damage caused by excess light. Photoprotection is essential for photosynthesis to proceed in oxygenic environments either by scavenging harmful reactive intermediates or preventing their accumulation to avoid photoinhibition. Carotenoids play a key role in protecting photosynthesis from the toxic effect of over-excitation; under excess light conditions, plants accumulate a specific carotenoid, zeaxanthin, that was shown to increase photoprotection. In this work we genetically dissected different components of zeaxanthin-dependent photoprotection. By using time-resolved differential spectroscopy in vivo, we identified a zeaxanthin-dependent optical signal characterized by a red shift in the carotenoid peak of the triplet-minus-singlet spectrum of leaves and pigment-binding proteins. By fractionating thylakoids into their component pigment binding complexes, the signal was found to originate from the monomeric Lhcb4-6 antenna components of Photosystem II and the Lhca1-4 subunits of Photosystem I. By analyzing mutants based on their sensitivity to excess light, the red-shifted triplet-minus-singlet signal was tightly correlated with photoprotection in the chloroplasts, suggesting the signal implies an increased efficiency of zeaxanthin in controlling chlorophyll triplet formation. Fluorescence-detected magnetic resonance analysis showed a decrease in the amplitude of signals assigned to chlorophyll triplets belonging to the monomeric antenna complexes of Photosystem II upon zeaxanthin binding; however, the amplitude of carotenoid triplet signal does not increase correspondingly. Results show that the high light-induced binding of zeaxanthin to specific proteins plays a major role in enhancing photoprotection by modulating the yield of potentially dangerous chlorophyll-excited states in vivo and preventing the production of singlet oxygen.

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.

8 páginas, 6 figuras . En la sección "Acknowledgments" se incluye la siguiente mención "The authors are grateful to I. Barrera, M. Gil, A. Lobillo, J. Navarro, M.E. Orejas, A. Pintado, B. Rábago, E. Seriñá and E. Zuazua for their hard work at the field site and for their helpful comments.", Photosynthetic performance was monitored during two consecutive summers in four co-occurring evergreen Mediterranean tree species growing on a south-facing rocky slope. In response to midday water stress, the drought-avoiding species Pinus halepensis Mill. exhibited marked stomatal closure (gs) but no changes in stem water potential (Ψs), whereas the drought-tolerant species Quercus coccifera L., Q. ilex ssp. ballota (Desf.) Samp. and Juniperus phoenicea L. displayed declines in midday gs and Ψs. The higher resistance to CO2 influx in needles of P. halepensis compared with the other species did not result in either a proportional increase in non-radiative dissipation of excess energy or photo-inactivation of photosystem II (PSII). No significant differences were found among species either in the de-epoxidation state of the xanthophyll cycle (DPS) or in the pool of its components on a total chlorophyll basis (VAZ). Despite contrasting midday assimilation rates, the three drought-tolerant species all exhibited a pronounced drop in photochemical efficiency at midday that was characterized by a decrease in the excitation capture efficiency of the open PSII centers. Although photoinhibition was not fully reversed before dawn, it apparently did not result in cumulative photo-damage. Thus, the drought-avoiding and drought-tolerant species employed different mechanisms for coping with excess light during the midday depression in photosynthesis that involved contrasting midday photochemical efficiencies of PSII and different degrees of dynamic photoinhibition as a photo-protective mechanism. These behaviors may be related to the different mechanisms employed by drought-avoiding and drought-tolerant species to withstand water deficit., This research was supported by a research grant from CICYT (CLI95-1902).