The Effects of UV Radiation on Chloroplast Clumping and Photosynthesis in the Seagrass Halophila stipulacea

Since potentially harmful ultraviolet radiation (UVR, 280–400 nm) and high photosynthetically active radiation (PAR, 400–700 nm) are present in the shallow waters of the Gulf of Aqaba where part of the seagrass Halophila stipulacea's population thrives, we examined the effects of high PAR with and without UVR on its photosynthesis and midday chloroplast “clumping phenomenon” (Sharon and Beer 2008). It was found that midday clumping occurred only under high PAR in the presence of UVR, which resulted in a 44% reduction in the absorption cross section (or absorption factor, AF) of the leaves and, accordingly, a parallel lowering of midday electron transport rates (ETR). In addition, UVR had a direct effect on the photosynthetic apparatus by lowering quantum yields and, thus, ETRs, while pigment relations remained unaltered. We conclude that the potentially harmful effects of UVR and high PAR on the photosynthetic apparatus of Halophila stipulacea are mitigated by their activation of chloroplast clumping, which functions as a means of protecting most chloroplasts from high irradiances, including UVR

Effects of in situ shading on the photophysiology of Zostera marina and Cymodocea nodosa

The effects of light reduction were investigated in natural stands of the seagrasses Zostera marina and Cymodocea nodosa in Ria Formosa coastal lagoon, southern Portugal. Four shading plots and a control were set in each of two neighbouring meadows (2-3 m depth), each dominated by one species. The experiment lasted for 3 weeks, at the end of which the response of plant photosynthesis to light was determined via oxygen electrode measurements. Tissue samples were also analysed for photosynthetic pigment, soluble protein, soluble sugar and malondialdehyde contents. All plants presented a shade-adapted profile, mostly revealed by their biochemical composition. In both species the chlorophyll a/chlorophyll b ratio decreased sharply whereas the total chlorophyll/total carotenoids and the total chlorophyll/soluble protein ratios increased. Soluble protein content was reduced more noticeably in Z. marina. Soluble sugars dropped almost 40% in Z. marina leaves and roots, a more pronounced effect than the one observed in C. nodosa. Overall, Z. marina revealed to be more sensitive than C. nodosa to reductions in incident irradiance, suggesting that it will be more sensitive to human-induced disturbances that result in an increase of water turbidity

Algae in fish feed: performances and fatty acid metabolism in juvenile Atlantic Salmon

Algae are at the base of the aquatic food chain, producing the food resources that fish are adapted to consume. Previous studies have proven that the inclusion of small amounts (<10% of the diet) of algae in fish feed (aquafeed) resulted in positive effects in growth performance and feed utilisation efficiency. Marine algae have also been shown to possess functional activities, helping in the mediation of lipid metabolism, and therefore are increasingly studied in human and animal nutrition. The aim of this study was to assess the potentials of two commercially available algae derived products (dry algae meal), Verdemin (derived from Ulva ohnoi) and Rosamin (derived from diatom Entomoneis spp.) for their possible inclusion into diet of Atlantic Salmon (Salmo salar). Fish performances, feed efficiency, lipid metabolism and final product quality were assessed to investigated the potential of the two algae products (in isolation at two inclusion levels, 2.5% and 5%, or in combination), in experimental diets specifically formulated with low fish meal and fish oil content. The results indicate that inclusion of algae product Verdemin and Rosamin at level of 2.5 and 5.0% did not cause any major positive, nor negative, effect in Atlantic Salmon growth and feed efficiency. An increase in the omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) content in whole body of fish fed 5% Rosamin was observed

Measuring seagrass photosynthesis: methods and applications

This review originates from a keynote lecture given at the recent 8th Group for Aquatic Productivity (GAP) workshop held in Eilat, Israel. Here we examine the most important methodologies for photosynthetic measurements in seagrasses and evaluate their applications, advantages and disadvantages, and also point out the most relevant results. The most commonly used methodologies are based on oxygen (O(2)) evolution and chlorophyll fluorescence measurements. O(2)-based methodologies allowed for the first approaches to evaluate seagrass productivity, whereas chlorophyll a fluorescence has more recently become the choice method for in situ experiments, particularly in evaluating photosynthetic responses to light and assessing stress responses. New methodologies have also emerged, such as O(2) optodes, underwater CO(2) flux measurements, geo-acoustic inversion and the eddy correlation technique. However, these new methods still need calibration and validation. Our analysis of the literature also reveals several significant gaps in relevant topics concerning seagrass photosynthesis, namely the complete absence of studies on deep-growing populations that photosynthesise under extreme low light conditions and the uncertainties about the true degree of seagrass carbon limitation, which limits our ability to predict responses to global changes

Photosynthetic responses of Halophila stipulacea to a light gradient. II. Acclimations following transplantation

Halophila stipulacea is the dominant seagrass in the Gulf of Aqaba (northern Red Sea), where it grows from the intertidal to depths exceeding 50 m. Its successful growth under such a broad irradiance gradient shows either a high plasticity or is caused by longer-term adaptations to the various depths, possibly resulting in the formation of ecotypes. In April 2008 we transplanted shoots of this seagrass between the extreme depths of its distribution at the study site (8 and 33 m) in order to evaluate its acclimation potential to various irradiances. We compared photosynthetic parameters derived from light response curves generated by PAM fluorometry (so-called rapid light curves, RLC) and measured chlorophyll a and b concentrations. RLCs from the shallow (similar to 400 pmol photons m(-2) s(-1) at midday) and deep (similar to 35 pmol photons m(-2) s(-1) at midday) sites were characteristic for high- and low-light growing plants, respectively, and the transplanted seagrasses acclimated to their new environments within 6 d, at which time their RLCs resembled those of the original plants growing at the depths to which they had been transplanted, Concentrations of both chlorophyll a and b decreased or increased when the plants were transferred to high- vs. low-light environments, respectively, but the chlorophyll a:b ratios remained constant. These fast changes in photosynthetic responses and light absorption characteristics in response to changing light environments points to Halophila stipulacea as being a highly plastic seagrass with regard to irradiance, which may partly explain its abundance across a wide range of irradiances along the depth gradient that it occupies

Acclimatization of symbiotic corals to mesophotic light environments through wavelength transformation by fluorescent protein pigments

The depth distribution of reef-building corals exposes their photosynthetic symbionts of the genus Symbiodinium to extreme gradients in the intensity and spectral quality of the ambient light environment. Characterizing the mechanisms used by the coral holobiont to respond to the low intensity and reduced spectral composition of the light environment in deeper reefs (greater than 20 m) is fundamental to our understanding of the functioning and structure of reefs across depth gradients. Here, we demonstrate that host pigments, specifically photoconvertible red fluorescent proteins (pcRFPs), can promote coral adaptation/acclimatization to deeper-water light environments by transforming the prevalent blue light into orange-red light, which can penetrate deeper within zooxanthellae-containing tissues; this facilitates a more homogeneous distribution of photons across symbiont communities. The ecological importance of pcRFPs in deeper reefs is supported by the increasing proportion of red fluorescent corals with depth (measured down to 45 m) and increased survival of colour morphs with strong expression of pcRFPs in long-term light manipulation experiments. In addition to screening by host pigments from high light intensities in shallow water, the spectral transformation observed in deeper-water corals highlights the importance of GFP-like protein expression as an ecological mechanism to support the functioning of the coral–Symbiodinium association across steep environmental gradients

Data from: Acclimatization of symbiotic corals to mesophotic light environments through wavelength transformation by fluorescent protein pigments

The depth distribution of reef-building corals exposes their photosynthetic symbionts of the genus Symbiodinium to extreme gradients in the intensity and spectral quality of the ambient light environment. Characterizing the mechanisms used by the coral holobiont to respond to the low intensity and reduced spectral composition of the light environment in deeper reefs (greater than 20 m) is fundamental to our understanding of the functioning and structure of reefs across depth gradients. Here, we demonstrate that host pigments, specifically photoconvertible red fluorescent proteins (pcRFPs), can promote coral adaptation/acclimatization to deeper-water light environments by transforming the prevalent blue light into orange-red light, which can penetrate deeper within zooxanthellae-containing tissues; this facilitates a more homogeneous distribution of photons across symbiont communities. The ecological importance of pcRFPs in deeper reefs is supported by the increasing proportion of red fluorescent corals with depth (measured down to 45 m) and increased survival of colour morphs with strong expression of pcRFPs in long-term light manipulation experiments. In addition to screening by host pigments from high light intensities in shallow water, the spectral transformation observed in deeper-water corals highlights the importance of GFP-like protein expression as an ecological mechanism to support the functioning of the coral&ndash;Symbiodinium association across steep environmental gradients.,Discosoma ImagesUnprocessed chlorophyll emission images at different excitation wavelengths in Discosoma.Suspension ImagesUnprocessed chlorophyll emission images at different excitation wavelengths in zooxanthellae suspension.ILM for DryadRaw data used to produce figures in the manuscript.,</span

Photosynthetic responses of Haalophila stipulacea to a light gradient. I. In situ energy partitioning of non-photochemical quenching

The quantum yield of photosystem II (phi(II), also termed Delta F/F-m' or F-v/F-m in light- or dark-acclimated plants, respectively) of the tropical seagrass Halophila stipulacea was measured in situ using modulated fluorescence techniques over diel periods at a range of depths. Photosynthetic electron transport rates (ETRs), as derived from phi(II) values at specific ambient photosynthetically available radiation (PAR) irradiances, increased in direct proportion to increasing irradiance in the morning and, at shallow sites (7 to 10 m), reached saturating rates and then declined in the afternoon with lower PAR-specific ETRs. On the other hand, plants at 32 to 33 m showed no saturation even at midday, and the percentage reduction in PAR-specific afternoon ETRs was less than that of the shallower plants. The use of an automated shutter in the measuring device enabled non-photochemical quenching due to down-regulation and basal intrinsic non-radiative decay to be distinguished. While midday values of down-regulation were lower in deeper water, basal intrinsic non-radioactive decay remained fairly constant at 30 to 40% at all depths, with more variation in shallow waters. The maximal phi(II) (i.e. F-v/F-m) reached similar values at midnight regardless of depth. H. stipulacea acclimates to the widely varying irradiances across this depth gradient by regularly modulating down-regulation-based non-photochemical quenching processes, while dissipating a large proportion of light energy through intrinsic decay regardless of depth

ILM for Dryad

Raw data used to produce figures in the manuscript

Probing the Structural Flexibility of the Human Copper Metallochaperone Atox1 Dimer and Its Interaction with the CTR1 C‑Terminal Domain

Both the essentiality and the toxicity of copper in human, yeast, and bacteria cells require precise mechanisms for acquisition, intimately linked to controlled distribution, which have yet to be fully understood. This work explores one aspect in the copper cycle, by probing the interaction between the human copper chaperone Atox1 and the c-terminal domain of the copper transporter, CTR1, using electron paramagnetic resonance (EPR) spectroscopy and circular dichroism (CD). The data collected here shows that the Atox1 keeps its dimer nature also in the presence of the CTR1 c-terminal domain; however, two geometrical states are assumed by the Atox1. One is similar to the geometrical state reported by the crystal structure, while the latter has not yet been constructed. In the presence of the CTR1 c-terminal domain, both states are assumed; however, the structure of Atox1 is more restricted in the presence of the CTR1 c-terminal domain. This study also shows that the last three amino acids of the CTR1 c-terminal domain, HCH, are important for maintaining the crystal structure of the Atox1, allowing less structural flexibility and improved thermal stability of Atox1