A Supercomplex, of Approximately 720 kDa and Composed of Both Photosystem Reaction Centers, Dissipates Excess Energy by PSI in Green Macroalgae Under Salt Stress.

The thylakoid membranes of plants play a critical role in electron transfer and energy fixation, and are highly dynamic. So far, studies on the thylakoid membranes have mainly focused on microalgae and higher plants, yet very little information is available on the macroalgal thylakoids. Here, we studied the structure and organization of the thylakoid membranes in Ulva prolifera, a representative species of the green macroalgae. We found that U. prolifera had few but long loosely stacked membranes which lack the conventional grana found in higher plants. However, the thylakoid membrane complexes demonstrate lateral heterogeneity. Moreover, we found a supercomplex composed of PSII, light-harvesting complex II (LHCII) and PSI from U. prolifera under salt stress. The supercomplex is approximately 720 kDa, and includes the two important photoprotection proteins, the PSII S subunit (PsbS) and the light-harvesting complex stress-related protein (LhcSR), as well as xanthophyll cycle pigments (violaxanthin, antheraxanthin and zeaxanthin). Time-resolved fluorescence analysis suggested that, in the supercomplex, excitation energy could efficiently be transferred from PSII to PSI, even when PSII was inhibited, a function which disappeared when the supercomplex was incubated in mild detergent. We suggest that the supercomplex might be an important mechanism to dissipate excess energy by PSI in green macroalgae under salt stress.

Desiccation tolerance in the chlorophyte green alga Ulva compressa: does cell wall architecture contribute to ecological success?

MAIN CONCLUSION: Desiccation leads to structural changes of the inner pectic cell wall layers in Ulva compressa. This contributes to protection against mechanical damage due to desiccation-rehydration cycles. Ulva compressa, characterized by rbcL phylogeny, is a common species in the Mediterranean Sea. Ulva as an intertidal species tolerates repeated desiccation-rehydration cycles in nature; the physiological and structural basis were investigated under experimental conditions here. Desiccation to 73% relative water content (RWC) led to a significant decrease of the maximum quantum yield of photosystem II (F v/F m) to about half of the initial value. A reduction to 48 or 27% RWC caused a more drastic effect and thalli were only able to recover fully from desiccation to 73% RWC. Relative electron transport rates were stimulated at 73% RWC, but decreased significantly at 48 and 27% RWC, respectively. Imaging-PAM analysis demonstrated a homogenous desiccation process within individual thallus discs. The different cell wall layers of U. compressa were characterized by standard staining procedures, i.e. calcofluor white and aniline blue for structural components (cellulose, callose), ruthenium red for pectins and toluidine blue for acidic polysaccharides. Already a reduction to 73% RWC caused severe changes of the cell walls. The inner pectin-rich layers followed the shrinkage process of the cytoplasm, while the outer denser fibrillar layers maintained their shape. In this way, the thalli were not plasmolyzed during water loss, and upon recovery not negatively influenced by any mechanical damage. Transmission electron microscopy corroborated the arrangement of the different layers clearly distinguishable by their texture and electron density. We suggest the flexibility of the pectin-rich cell wall layers as a major contribution to desiccation tolerance in Ulva.

Hot embossed microtopographic gradients reveal morphological cues that guide the settlement of zoospores.

Among different surface cues, the settlement of cells and larvae of marine macrofouling organisms has been found to be strongly influenced by surface microtopographies. In this article, the settlement of zoospores of the green alga Ulva linza on a surface topographic gradient has been investigated. "Honeycomb" gradient structures with feature sizes ranging from 1 to 10 µm were prepared by hot embossing, and the effect on the density of spores that attached in settlement assays was quantified. The highest density of spores was found when the size of the microstructures was similar to or larger than the size of the spores. With decreasing size of the structures, spore settlement density decreased. Interestingly, spore settlement density correlated with the Wenzel roughness of the surfaces. "Kink sites" on the surface played an important role and resembled preferred attachment positions. Furthermore, the gradients allowed the minimum pit size that the spores were able to squeeze into to be determined.

Image Cytometric Analysis of Algal Spores for Evaluation of Antifouling Activities of Biocidal Agents.

Chemical biocides have been widely used as marine antifouling agents, but their environmental toxicity impose regulatory restriction on their use. Although various surrogate antifouling biocides have been introduced, their comparative effectiveness has not been well investigated partly due to the difficulty of quantitative evaluation of their antifouling activity. Here we report an image cytometric method to quantitatively analyze the antifouling activities of seven commercial biocides using Ulva prolifera as a target organism, which is known to be a dominant marine species causing soft fouling. The number of spores settled on a substrate is determined through image analysis using the intrinsic fluorescence of chlorophylls in the spores. Pre-determined sets of size and shape of spores allow for the precise determination of the number of settled spores. The effects of biocide concentration and combination of different biocides on the spore settlement are examined. No significant morphological changes of Ulva spores are observed, but the amount of adhesive pad materials is appreciably decreased in the presence of biocides. It is revealed that the growth rate of Ulva is not directly correlated with the antifouling activities against the settlement of Ulva spores. This work suggests that image cytometric analysis is a very convenient, fast-processable method to directly analyze the antifouling effects of biocides and coating materials.

In vitro exposure of Ulva lactuca Linnaeus (Chlorophyta) to gasoline - Biochemical and morphological alterations.

Refined fuels have considerable share of pollution of marine ecosystems. Gasoline is one of the most consumed fuel worldwide, but its effects on marine benthic primary producers are poorly investigated. In this study, Ulva lactuca was chosen as a biological model due to its cosmopolitan nature and tolerance to high levels and wide range of xenobiotics and our goal was to evaluate the effects of gasoline on ultrastructure and metabolism of that seaweed. The experimental design consisted of in vitro exposure of U. lactuca to four concentrations of gasoline (0.001%, 0.01%, 0.1%, and 1.0%, v/v) over 30 min, 1 h, 12 h, and 24 h, followed by cytochemical, SEM, and biochemical analysis. Increase in the number of cytoplasmic granules, loss of cell turgor, cytoplasmic shrinkage, and alterations in the mucilage were some of the ultrastructural alterations observed in thalli exposed to gasoline. Decrease in carotenoid and polyphenol contents, as well as increase of soluble sugars and starch contents were associated with the time of exposure to the xenobiotic. In combination, the results revealed important morphological and biochemical alterations in the phenotype of U. lactuca upon acute exposure to gasoline. This seaweed contain certain metabolites assigned as candidates to biomarkers of the environmental stress investigated and it is thought to be a promise species for usage in coastal ecosystems perturbation monitoring system. In addition, the findings suggest that U. lactuca is able to metabolize gasoline hydrocarbons and use them as energy source, acting as bioremediator of marine waters contaminated by petroleum derivatives.

Bacterial extracellular polymeric substances and their effect on settlement of zoospore of Ulva fasciata.

The extracellular polymeric substances (EPSs) secreted by Bacillus flexus (GU592213) were estimated to have the molecular weight of approximately 1528 and 33,686 kDa with the elemental composition of Na, P, Mg, C, O, Cl and S. The (1)H NMR and FT-IR analysis of EPS confirmed the presence of different aliphatic and aromatic groups. The EPS was amorphous in nature with an average particle size of 13.969 µm (d 0.5) and roughness of 193 nm. The GC-MS analysis has revealed different monosaccharides such as fucose, ribose, xylose, galactose, mannose and glucose. Oligo and polysaccharides were detected with MALDI TOF-TOF MS. The bacterial EPS for the first time tested as a natural substratum for settle of zoospores of Ulva fasciata by incubating for various durations ranging from 2h to 48 h. The zoospore settlement on EPS coated cover slips progressively increased with incubation time in axenic cultures over controls. The EPS, thus investigated in this study was found to facilitate the primary settlement of spores that play crucial role in recruitment of macroalgal communities in coastal environment including intertidal regions.

Sustainable and hierarchical porous Enteromorpha prolifera based carbon for CO2 capture.

Nitrogen-containing porous carbon was synthesized from an ocean pollutant, Enteromorpha prolifera, via hydrothermal carbonization and potassium hydroxide activation. Carbons contained as much as 2.6% nitrogen in their as-prepared state. Physical and chemical properties were characterized by XRD, N(2) sorption, FTIR, SEM, TEM, and elemental analysis. The carbon exhibited a hierarchical structure with interconnected microporosity, mesoporosity and macroporosity. Inorganic minerals in the carbon matrix contributed to the development of mesoporosity and macroporosity, functioning as an in situ hard template. The carbon manifested high CO(2) capacity and facile regeneration at room temperature. The CO(2) sorption performance was investigated in the range of 0-75°C. The dynamic uptake of CO(2) is 61.4 mg/g and 105 mg/g at 25°C and 0°C, respectively, using 15% CO(2) (v/v) in N(2). Meanwhile, regeneration under Ar at 25°C recovered 89% of the carbon's initial uptake after eight cycles. A piecewise model was employed to analyze the CO(2) adsorption kinetics; the Avrami model fit well with a correlation coefficient (R(2)) of 0.98 and 0.99 at 0°C and 25°C, respectively.