Effect of pre-incubation irradiance on survival of cryopreserved gametophytes of Undaria pinnatifida (Phaeophyta) and morphology of sporophytes formed from the gametophytes

Gametophyte strains originating from indigenous sporophytes of Undaria pinnatifida (Harvey) Suringar in Iwate Prefecture, Northeast Japan, were maintained for 9–10 months at 45 μmol photons m⁻² s⁻¹. Before cryopreservation in liquid nitrogen for more than 12 h (1–14 days) using a two-step cooling method with a mixture of cryoprotectants (10% l-proline and 10% glycerol), these were pre-incubated for 2, 4 and 8 months at 15 μmol photons m⁻² s⁻¹. After 1 week of thawing, no surviving gametophytes were detected in the strains without pre-incubation, but both the female and male gametophytes, pre-incubated for more than 4 months, showed high survival rates (43–60% for females and 64–100% for males). This revealed the induction of freezing tolerance by incubation at low irradiance. Thereafter, sporophytes derived from cryopreserved gametophytes and subcultured gametophytes, stored under pre-incubation conditions, were formed from the strain, and a morphological comparison was conducted with 10 characters (stipe length, stipe wet weight, blade length, blade wet weight, blade width, incision depth, blade thickness, sporophyll length, sporophyll wet weight, and sporophyll width). The morphology of the sporophytes formed from the cryopreserved gametophytes corresponded well with that of the subcultured gametophytes from the same strain. The results suggest that the cryopreservation method is applicable for preserving culture stocks of U. pinnatifida to be used in mariculture.     

Photoacclimation and Photoprotection of Juvenile Sporophytes of Macrocystis pyrifera (Laminariales,Phaeophyceae) Under High-light Conditions During Short-term Shallow-water Cultivation1

This study was designed to understand better if and how juvenile sporophytes of Macrocystis pyrifera can photoacclimate to high-light conditions when transplanted from 10 to 3 meters over 7 d. Acclimation of adult sporophytes to light regimes in the bathymetric gradient has been extensively documented. It primarily depends on photoacclimation and translocation of resources among blades. Among other physiological differences, juvenile sporophytes of M. pyrifera lack the structural complexity shown by adults. As such, juveniles may primarily depend on their photoacclimation capacities to maintain productivity and even avoid mortality under changing light regimes. However, little is known about how these mechanisms operate in young individuals. The capacity of sporophytes to photoacclimate was assessed by examining changes in their photosynthetic performance, pigment content, and bio-optical properties of the blade. Sporophytes nutritional status and oxidative damage were also determined. Results showed that juvenile sporophytes transplanted to shallow water were able to regulate light harvesting by reducing pigment concentration, and thus, absorptance and photosynthetic efficiency. Also, shallow-water sporophytes notably enhanced the dissipation of light energy as heat (NPQ) as a photoprotective mechanism. Generally, these adjustments allowed sporophytes to manage the absorption and utilization of light energy, hence reducing the potential for photo-oxidative damage. Furthermore, no substantial changes were found in the internal reserves (i.e., soluble carbohydrates and nitrogen) of these sporophytes. To our knowledge, these results are the first to provide robust evidence of photoprotective and photoacclimation strategies in juveniles of M. pyrifera, allowing them to restrict or avoid photodamage during shallow-water cultivation.     

Population biology of the intertidal kelp, Alaria marginata Postels and Ruprecht: A non-fugitive annual

Persistence of annual plant populations requires sufficient seeds and suitable habitat for development and growth each year. Competition with perennials may prevent within site persistence and result in “fugitive” annual populations. Comparisons have been made between the population biology of annual macroalgae and terrestrial plants, but demographic information necessary to make strong comparisons is lacking for most of these algae, and life history differences may make such comparisons questionable. We studied population dynamics of the kelp Alaria marginata to determine if it was an annual and, if so, how populations persisted. This kelp is the dominant macroalga on exposed mid to low rocky intertidal shores along the Big Sur coast of California. Experimental clearings at two sites were used to assess recruitment timing and survivorship. Sporophytes were collected monthly to determine growth and fecundity. Recruitment occurred in late winter to early spring, primarily on geniculate corallines and residual A. marginata holdfasts. Thinning was inversely related to density, and occurred during the February through July growing season as larger thalli rapidly increased in length (up to 1.4 m month^− 1) and formed a thick canopy. Sorus development was positively related to size, began as early as March, peaked in late August-October, and decreased as adults were removed by winter surf. Spore release was generally highest (10⁸-10⁹ spores individual^− 11 h^− 1) between October and January and associated with high water motion. Survivorship of sporophytes beyond one year was < 1%, showing the populations were annual.Field observations and experiments on effects of canopy clearing, season of clearing, and influence of substrate type on recruitment were done to assess how these annual populations persist. Massive spore production at the onset of fall storms, survival of microscopic stages for 3-4 months facilitated by microhabitat refuges, rapid growth, large size and rapid maturation of sporophytes contributed to persistence. Furthermore, the dense stands with thick canopies may suppress potential competitors via shading and abrasion. Rather than being a fugitive, this combination of growth and life history features enables A. marginata and perhaps other large, annual kelps to maintain perennial populations.     

Horizontal or vertical photobioreactors? How to improve microalgae photosynthetic efficiency

The productivity of a vertical outdoor photobioreactor was quantitatively assessed and compared to a horizontal reactor. Daily light cycles in southern Spain were simulated and applied to grow the microalgae Chlorella sorokiniana in a flat panel photobioreactor.The maximal irradiance around noon differs from 400 μmol photons m⁻² s⁻¹ in the vertical position to 1800 μmol photons m⁻² s⁻¹ in the horizontal position. The highest volumetric productivity was achieved in the simulated horizontal position, 4 g kg culture⁻¹ d⁻¹. The highest photosynthetic efficiency was found for the vertical simulation, 1.3 g of biomass produced per mol of PAR photons supplied, which compares favorably to the horizontal position (0.85 g mol⁻¹) and to the theoretical maximal yield (1.8 g mol⁻¹). These results prove that productivity per unit of ground area could be greatly enhanced by placing the photobioreactors vertically.     

Diurnal movements of chloroplasts in Halophila stipulacea and their effect on PAM fluorometric measurements of photosynthetic rates

Since diurnal chloroplast movements in Halophila stipulacea were described by Drew in 1979, this phenomenon has not been studied further for seagrasses. In addition to an apparent photoprotective role, such movements may affect the measurements of photosynthetic rates based on pulse amplitude modulated (PAM) fluorometry. This is because calculations of electron transport rates (ETR) are directly affected by the light absorption of the leaves (or the so-called absorption factor, AF), the latter of which changes with the movements of the chloroplasts. In this work, we therefore determined chloroplast clumping and dispersal, and measured AFs, chlorophyll contents and PAM fluorescence diurnally for H. stipulacea grown under two irradiance regimes. Diurnal chloroplast clumping occurred in high-light grown (HL) plants (∼450 μmol photons m⁻² s⁻¹ during midday), which was accompanied by a decrease in AF values (from 0.56 in the early morning to 0.34 at midday) but not in the chlorophyll content. Also, non-photochemical quenching (measured as NPQ) increased during the day in these plants. No such chloroplast movements and, thus, no diurnal changes in AF values (0.60 ± 0.04 throughout the day), and no changes in NPQ, were found in low-light grown (LL) plants (∼150 μmol photons m⁻² s⁻¹ during midday). As a consequence of the chloroplast clumping in HL plants, and its effect on AF values, maximal ETRs did not differ significantly between HL and LL plants. This finding thus shows the importance of taking into account changing AF values along the day when calculating ETRs of H. stipulacea, and other seagrasses potentially featuring diurnally changing AFs, under high-irradiance conditions.     

Chemical profile of the North American native Myriophyllum sibiricum compared to the invasive M. spicatum

Myriophyllum spicatum L. is a nonindigenous invasive plant in North America that can displace the closely related native Myriophyllum sibiricum Komarov. We analyzed the chemical composition (including: C, N, P, polyphenols, lignin, nonpolar extractables, and sugars) of M. spicatum and M. sibiricum and determined how the chemistry of the two species varied by plant part with growing environment (lake versus tank), irradiance (full sun versus 50% shading), and season (July through September). M. spicatum had higher concentrations of carbon, polyphenols and lignin (C: 47%; polyphenols: 5.5%; lignin: 18%) than M. sibiricum (C: 42%; polyphenols: 3.7%; lignin: 9%) while M. sibiricum had a higher concentration of ash under all conditions (12% versus 8% for M. spicatum). Apical meristems of both species had the highest concentration of carbon, polyphenols, and tellimagrandin II, followed by leaves and stems. Tellimagrandin II was present in apical meristems of both M. spicatum (24.6 mg g⁻¹ dm) and M. sibiricum (11.1 mg g⁻¹ dm). Variation in irradiance from 490 (shade) to 940 (sun) μmol of photons m⁻² s⁻¹ had no effect on C, N, and polyphenol concentrations, suggesting that light levels above 490 μmol of photons m⁻² s⁻¹ do not alter chemical composition. The higher concentration of polyphenols and lignin in M. spicatum relative to M. sibiricum may provide advantages that facilitate invasion and displacement of native plants.     

Influence of ammonium sulphate feeding time on fed-batch Arthrospira (Spirulina) platensis cultivation and biomass composition with and without pH control

Previous work demonstrated that a mixture of NH₄Cl and KNO₃ as nitrogen source was beneficial to fed-batch Arthrospira (Spirulina) platensis cultivation, in terms of either lower costs or higher cell concentration. On the basis of those results, this study focused on the use of a cheaper nitrogen source mixture, namely (NH₄)₂SO₄ plus NaNO₃, varying the ammonium feeding time (T = 7-15 days), either controlling the pH by CO₂ addition or not. A. platensis was cultivated in mini-tanks at 30 °C, 156 μmol photons m⁻² s⁻¹, and starting cell concentration of 400 mg L⁻¹, on a modified Schlösser medium. T = 13 days under pH control were selected as optimum conditions, ensuring the best results in terms of biomass production (maximum cell concentration of 2911 mg L⁻¹, cell productivity of 179 mg L⁻¹ d⁻¹ and specific growth rate of 0.77 d⁻¹) and satisfactory protein and lipid contents (around 30% each).     

Chromatic photoacclimation, photosynthetic electron transport and oxygen evolution in the Chlorophyll d-containing oxyphotobacterium Acaryochloris marina

Changes in photosynthetic pigment ratios showed that the Chlorophyll d-dominated oxyphotobacterium Acaryochloris marina was able to photoacclimate to different light regimes. Chl d per cell were higher in cultures grown under low irradiance and red or green light compared to those found when grown under high white light, but phycocyanin/Chl d and carotenoid/Chl d indices under the corresponding conditions were lower. Chl a, considered an accessory pigment in this organism, decreased respective to Chl d in low irradiance and low intensity non-white light sources. Blue diode PAM (Pulse Amplitude Modulation) fluorometry was able to be used to measure photosynthesis in Acaryochloris. Light response curves for Acaryochloris were created using both PAM and O₂ electrode. A linear relationship was found between electron transport rate (ETR), measured using a PAM fluorometer, and oxygen evolution (net and gross photosynthesis). Gross photosynthesis and ETR were directly proportional to one another. The optimum light for white light (quartz halogen) was about 206 ± 51 μmol m^− 2 s^− 1 (PAR) (Photosynthetically Active Radiation), whereas for red light (red diodes) the optimum light was lower (109 ± 27 μmol m^− 2 s^− 1 (PAR)). The maximum mean gross photosynthetic rate of Acaryochloris was 73 ± 7 μmol mg Chl d^− 1 h^− 1. The gross photosynthesis/respiration ratio (P_g/R) of Acaryochloris under optimum conditions was about 4.02 ± 1.69. The implications of our findings will be discussed in relation to how photosynthesis is regulated in Acaryochloris.     

Primary production,respiration and calcification of the temperate free-living coralline alga Lithothamnion corallioides

Calcification and primary production responses to irradiance in the temperate coralline alga Lithothamnion corallioides were measured in summer 2004 and winter 2005 in the Bay of Brest. Coralline algae were incubated in dark and clear bottles exposed to different irradiances. Net primary production reached 1.5 μmol C g⁻¹ dry wt h⁻¹ in August and was twice as high as in January–February. Dark respiration showed significant seasonal variations, being three-fold higher in summer. Maximum calcification varied from 0.6 μmol g⁻¹ dry wt h⁻¹ in summer 2004 to 0.4 μmol g⁻¹ dry wt h⁻¹ in winter 2005. According to P–E curves and the daily course of irradiance, estimated daily net production and calcification reached 131 μg C g⁻¹ dry wt and 970 μg CaCO₃ g⁻¹ dry wt in summer 2004, and 36 μg C g⁻¹ dry wt and 336 μg CaCO₃ g⁻¹ dry wt in winter 2005. The net primary production of natural L. corallioides populations in shallow waters was estimated at 10–600 g C m⁻² y⁻¹, depending on depth and algal biomass. The mean annual calcification of L. corallioides populations varied from 300 to 3000 g CaCO₃ m⁻². These results are similar to those reported for tropical coralline algae in terms of carbon and carbonate productivity. Therefore, L. corallioides can be considered as a key element of carbon and carbonate cycles in the shallow coastal waters where they live.     

Accumulation of lead by free and immobilized cyanobacteria with special reference to accumulation factor and recovery

Lead accumulation by free and immobilized cyanobacteria, Lyngbya majuscula and Spirulina subsalsa was studied. Exponentially growing biomass was exposed to 1-20 mg L⁻¹ of Pb(II) solution at pH 6, 7 and 8 for time periods ranging from 10 min to 48 h. L. majuscula accumulated 10 times more Pb (13.5 mg g⁻¹) than S. subsalsa (1.32 mg g⁻¹) at pH 6 within 3 h of exposure to 20 mg L⁻¹ Pb(II) solution and 76% of the Pb could be recovered using 0.1 M EDTA. This chelator (2 μM) did not influence Pb accumulation whereas 100 μM citrate increased that of S. subsalsa 6- to 8-fold. L. majuscula filaments enmeshed in a glass wool packed in a column removed 95.8% of the Pb from a 5 mg L⁻¹ Pb solution compared to free and dead biomass which removed 64 and 33.6% Pb respectively. A 92.5% recovery of accumulated Pb from the immobilized biomass suggests that repeated absorption-desorption is possible.     

Sorgoleone,a sorghum root exudate: Algicidal activity and acute toxicity to the ricefish Oryzias latipes

The discovery of natural and natural-based compounds has resulted in its application as an alternative to synthetic algicides to control harmful algae in aquatic systems. Of the many natural-product-based algicides, sorgoleone, a natural plant product from Sorghum bicolor root exudates has been investigated for its controlling effect on different algal species and its acute fish toxicity. Growth of the blue green algal species Microcystis aeruginosa Kützing was completely inhibited by the crude methanol extract of sorghum root at 20 μg mL⁻¹. The most noticeable inhibition was observed in the bioassay of n-hexane soluble extract, where 98% growth inhibition occurred in M. aeruginosa at the concentration of 1.25 μg mL⁻¹. Sorgoleone very effectively controlled blue green algae inhibiting 97% of M. aeruginosa at 0.5 μg mL⁻¹ and 99% of Anabaena affinis Lemmermann at 4 μg mL⁻¹. In contrast, inhibition of the green algae species Chlorella vulgaris Beijerinck and Scenedensmus spp. at 16 μg mL⁻¹ sorgoleone was 87 and 68%, respectively. There were no mortalities or adverse effects observed in any of the fish exposed to water control, solvent control, and a nominal concentration of 1 μg mL⁻¹ during the test period. The no observed effect concentration (NOEC) value was 1.5 μg mL⁻¹ for the tested fish (O. latipes). Sorgoleone can be considered as an effective and an ecologically and environmentally sustainable approach to controlling harmful algae.     

Short term effects of hypoxia and bioturbation on solute fluxes, denitrification and buffering capacity in a shallow dystrophic pond

The effects of short term hypoxia on bioturbation activity and inherent solute fluxes are scarcely investigated even if increasing number of coastal areas are subjected to transient oxygen deficits. In this work dark fluxes of oxygen (O₂), dissolved inorganic carbon (TCO₂) and nutrients across the sediment-water interface, as well as rates of denitrification (isotope pairing), were measured in intact sediment cores collected from the dystrophic pond of Sali e Pauli (Sardinia, Italy). Sediments were incubated at 100, 70, 40 and 10% of O₂ saturation in the overlying water, with both natural benthic communities, dominated by the polychaete Polydora ciliata (11.100 ± 2.500  ind. m^− 2), and after the addition of individuals of the deep-burrower polychaete Hediste diversicolor. Below an uppermost oxic layer of ~ 1 mm, sediments were highly reduced, with up to 6 mM of S²⁻ in the 5 mm layer. Flux of S²⁻ and O₂ calculated from pore water gradients were 8.61 ± 1.12 and − 2.27 ± 0.56 mmol m^− 2 h^− 1, respectively. However, sediment oxygen demand (SOD) calculated from core incubation was − 10.52 ± 0.33 mmol m^− 2 h^− 1, suggesting a major contribution of P. ciliata to O₂-mediated sulphide oxidation. P. ciliata also strongly stimulated NH₄⁺ and PO₄³⁻ fluxes, with rates ~ 15 and ~ 30 folds higher, respectively, than those estimated from pore water gradients. P. ciliata activity was significantly reduced at 10% O₂ saturation, coupled to decreased rates of solutes transfer. The addition of H. diversicolor further stimulated SOD, NH₄⁺ efflux and SiO₂ mobilisation. Similarly to P. ciliata, the degree of stimulation of SOD and NH₄⁺ flux by H. diversicolor depended on the level of oxygen saturation. TCO₂ regeneration, respiratory quotients, PO₄³⁻ fluxes and denitrification of added ¹⁵NO₃⁻ were not affected by the addition of H. diversicolor, but depended upon the O₂ levels in the water column. Denitrification rates supported by water column ¹⁴NO₃⁻ and sedimentary nitrification were both negligible (< 0.5 µmol m^− 2 h^− 1). They were not significantly affected by oxygen saturation nor by bioturbation, probably due to the limited availability of NO₃⁻ in the water column (< 3 µM) and O₂ in the sediments. This study demonstrates for the first time the integrated short term effect of transient hypoxia and bioturbation on solute fluxes across the sediment-water interface within a simplified lagoonal benthic community.     

Exposure times in rapid light curves affect photosynthetic parameters in algae

Short-and long-duration light curves were applied to four macroalgae (Ulva sp., Codium fragile, Ecklonia radiata and Lessonia variegata), and two microalgal species (Chlorella emersonii and Chaetoceros muellerii). With increasing light curve duration, the maximal relative electron transport rate increased by a factor of three in E. radiata, and by factors of 1.25 and 1.23 in C. emersonii and L. variegata, respectively, but did not change in C. fragile and Ch. muellerii. The light saturation point E_k increased by 26 μmol photons m⁻² s⁻¹ in C. emersonii and 20 μmol photons m⁻² s⁻¹ in Ch. muellerii and E. radiata with elevated light curve exposure times. Oscillatory patterns of the continuous fluorescence readings reflect accumulation of Q_A. Continuous fluorescence values increased, or decreased, by approximately 10% within light curve increments. However, oscillations of 25% were not uncommon, which shows that cells are changing their photo-physiological response state during steady light conditions. Increasing dark acclimation times prior to light curve application lowered maximal relative electron transport rates in the C. emersonii (from 28 ± 1.7 to 25 ± 1.2 for 15 and 95 min dark acclimation in short-duration light curves respectively). This effect was counterbalanced by longer light curve application. It can therefore be concluded that manipulation of light exposure and dark incubation prior to the experiment affects the photosynthetic response, presumably due to different activation states of photosynthetic and photoprotective mechanisms. The highly species-specific photo-response patterns imply that a common rapid light curve protocol will generate artefacts in some species.     

Spectroscopic studies of the chlorophyll d containing photosystem I from the cyanobacterium, Acaryochloris marina

Absorbance difference spectroscopy and redox titrations have been applied to investigate the properties of photosystem I from the chlorophyll d containing cyanobacterium Acaryochloris marina. At room temperature, the (P740⁺ − P740) and (F_A/B⁻ − F_A/B) absorbance difference spectra were recorded in the range between 300 and 1000 nm while at cryogenic temperatures, (P740⁺A₁⁻ − P740A₁) and (³P740 − P740) absorbance difference spectra have been measured. Spectroscopic and kinetic evidence is presented that the cofactors involved in the electron transfer from the reduced secondary electron acceptor, phylloquinone (A₁⁻), to the terminal electron acceptor and their structural arrangement are virtually identical to those of chlorophyll a containing photosystem I. The oxidation potential of the primary electron donor P740 of photosystem I has been reinvestigated. We find a midpoint potential of 450 ± 10 mV in photosystem I-enriched membrane fractions as well as in thylakoids which is very similar to that found for P700 in chlorophyll a dominated organisms. In addition, the extinction difference coefficient for the oxidation of the primary donor has been determined and a value of 45,000 ± 4000 M^− 1 cm^− 1 at 740 nm was obtained. Based on this value the ratio of P740 to chlorophyll is calculated to be 1:~ 200 chlorophyll d in thylakoid membranes. The consequences of our findings for the energetics in photosystem I of A. marina are discussed as well as the pigment stoichiometry and spectral characteristics of P740.     

S-sulfonation of transthyretin is an important trigger step in the formation of transthyretin-related amyloid fibril

Senile systemic amyloidosis and familial amyloid polyneuropathy are caused by oxidative deposition of conformationally altered transthyretin (TTR). We identified oxidative modification of the 10th cysteine of TTR through S-sulfonation in vitro. Based on mass spectrometric analysis, we determined the spectrophotometric, western blotting, and fluororescent microscopic properties of TTR incubated with and without cysteine-S-sulfonate in acidic (pH 4) and alkaline (pH 8) conditions at 37°. The absorption of the aggregated TTR molecules increased more with incubation time and the concentration of cysteine-S-sulfonate at pH 4 than at pH 8. The Congo red binding to the S-sulfonated TTR at pH 4 was saturated with an apparent Bmax of 2.01 mol per mole of the S-sulfonated TTR and apparent K_D of 7.75 × 10⁻⁶ M. On the other hand, the Bmax of cysteinyl TTR was 1.38, and its K_D was 3.52 × 10⁻⁶ M while the Bmax of reduced TTR was 0.86, and its K_D was 2.86 × 10⁻⁶ M. Moreover, we detected positive amyloid fibril staining using Thioflavin T and Congo red with the S-sulfonated TTR but not with untreated or reduced TTR by microscopic fluororescent analysis. After modification of TTR in vitro, oligomers resisted reduction and denaturation was irreversibly induced, and which contributed differences in the Western blotting patterns obtained with four anti-TTR antibodies. In conclusion, this study showed that the formation of S-sulfonation of TTR through oxidative modifications of the thiol residue on the 10th cysteine of TTR is an important trigger step in the formation of transthyretin-related amyloid fibril.     

Light-dependent phosphate uptake of a submersed macrophyte Myriophyllum spicatum L.

The uptake kinetics of phosphate (Pi) by Myriophyllum spicatum was determined from adsorption and absorption under light and dark conditions. Pi uptake was light dependent and showed saturation following the Michaelis-Menten relation (in light: V = 16.91 × [Pi](1.335 + [Pi]), R² = 0.90, p < 0.001; in the dark: V = 5.13 × [Pi](0.351 + [Pi]), R² = 0.77, p < 0.001). Around 77% of the loss of Pi in the water column was absorbed into the tissue of M. spicatum, and only 23% was adsorbed on the surface of the plant shoots. Our study shows that M. spicatum shoots have a much higher affinity (in light: 3.9 μmol g⁻¹ dw h⁻¹ μM⁻¹; in the dark: 3.7 μmol g⁻¹ dw h⁻¹ μM⁻¹) and V_max (maximum uptake rate, shoot light) for Pi uptake than many other aquatic macrophytes (in light: 0.002-0.23 μmol g⁻¹ dw h⁻¹ μM⁻¹; in the dark: 0.002-0.19 μmol g⁻¹ dw h⁻¹ μM⁻¹), which may provide a competitive advantage over other macrophytes across a wide range of Pi concentrations.     

Effect of substituent dtp to optical properties of heterobimetallic M/Ag/S nest-shaped clusters (M = Mo, W)

Clusters [MoS₄Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (1), [WS₄Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (2) and [WOS₃Ag₃(PPh₃)₃{S₂P(OPrⁱ)₂}] (3) were synthesized by the reaction of (NH₄)₂MoS₄/(NH₄)₂WS₄, (NH₄)₂WOS₃ with Ag[S₂P(OPrⁱ)₂]. Their structures have been characterized by X-ray diffraction. The clusters consist of a distorted tetrahedral MS₄ (or MOS₃) (M = Mo, W) with three Ag atoms and three sulfur atom bridges (Fig. 1), and resemble roughly that of cubane-like clusters. The nonlinear optical (NLO) properties were studied with an 8 ns pulsed laser at 532 nm. Its optical response to the incident light exhibits good optical absorptive and refractive effects, with α₂ = 1.56 × 10⁻¹⁰ m W⁻¹, n₂ = 3.87 × 10⁻¹⁷ m² W⁻¹ for cluster 1; α₂ = 1.33 × 10⁻¹⁰ m W⁻¹, n₂ = 6.52 × 10⁻¹⁷ m² W⁻¹for cluster 2; and α₂ = 2.54 × 10⁻¹⁰ m W⁻¹, n₂ = 4.07 × 10⁻¹⁷ m² W⁻¹ for cluster 3 for a 1.56 × 10⁻⁴ mol dm⁻³ CH₂Cl₂ solution.     

The effects of algae species and densities on the population growth of the marine rotifer, Colurella dicentra

Colurella dicentra clones isolated from bay water in the Mississippi Gulf Coast were cultured with artificial seawater. Experiments were conducted to determine the effects of six algae species (Nannochloropsis oculata, Tetraselmis chuii, Chaetoceros gracilis, Rhodomonas salina, Isochrysis galbana, and Prorocentrum micans), six C. gracilis densities, and six N. oculata densities (25,000, 50,000, 100,000, 250,000, 500,000, and 1,000,000 cells ml^− 1) on C. dicentra population growth. Algae type influenced rotifer production (p < 0.0001). C. gracilis treatment (9120 ± 3351SD) produced the highest number of rotifers followed by N. oculata (5760 ±2232SD). P. micans had the lowest number of rotifers, although not significantly different from numbers in T. chuii, R. salina, and I. galbana treatments (p > 0.05).The population growth rate (r) varied with algae species treatment. The highest values were recorded for C. gracilis treatment (0.22 to 0.26 d^− 1), followed by N. oculata (0.21 to 0.24 d^− 1), and the lowest for P. micans (− 0.19 to 0.14 d^− 1). C. gracilis and N. oculata densities had significant effects (p < 0.0001) on C. dicentra population growth. The highest rotifer production was recorded at a C. gracilis density of 100,000 cells ml^− 1, followed by 250,000 cells ml^− 1 and 50,000 cells ml^− 1. Algae densities of 500,000 cells ml^− 1 and above produced the lowest rotifer numbers. Population growth rate (r) varied with C. gracilis densities. The highest values were observed for C. gracilis concentrations of 100,000 cells ml^− 1 (0.17 to 0.19 d^− 1), and the lowest for concentrations of 500,000 cells ml^− 1 and above (− 0.19 to 0.09 d^− 1). The 100,000 cells ml^− 1N. oculata density gave the highest rotifer production followed by 50,000, 250,000, 25,000, and 500,000 cells ml^− 1. Algae densities of 1,000,000 cells ml^− 1 produced the lowest rotifer numbers. Population growth rate (r) varied with N. oculata densities, with the highest values obtained for algae densities of 100,000 cells ml^− 1 (0.35 to 0.40 d^− 1), and the lowest for concentrations of 1,000,000 cells ml^− 1 (0.05 to 0.012 d^− 1). This is the first report of C. dicentra in Mississippi Coastal waters, and perhaps the smallest marine rotifer species (93 by 49 μm) ever cultured successfully.     

Biological activity of l-2-azetidinecarboxylic acid,isolated from Polygonatum odoratum var. pluriflorum, against several algae

The biological activities of an aqueous fraction extracted from Polygonatum odoratum var. pluriflorum Owhi and of l-2-azetidinecarboxylic acid (AZC), purified from the extract, on the growth of several types of algae were tested. The aqueous fraction was prepared by methanol extraction of P. odoratum var. pluriflorum rhizomes followed by reverse partitioning with butanol. The aqueous extraction inhibited growth of the green alga Chlorella vulgaris by less than 10% at a concentration of 1000 mg L⁻¹. However, growth of the blue-green alga Microcystis aeruginosa was inhibited by 22.0%, 67.9%, and 87.1%, respectively, at 3.1, 6.2, and 12.5 mg extract L⁻¹. AZC was isolated from the aqueous extract and was shown to be the major active substance inhibiting algal growth. AZC concentrations higher than 25 μM inhibited growth, while at 400 μM, growth of the green algae C. vulgaris and Scenedesmus spp. was inhibited by 71.2% and 70.4%, respectively. In contrast, growth of the blue-green algae Anabaena affinis and M. aeruginosa was inhibited at concentrations greater than 1.6 and 0.2 μM, respectively, whereas 92% control required concentrations of 6.3 and 1.6 μM, respectively. AZC also suppressed the growth of the red-tide microalga Cochlodinium polykrikoides by 86.9% and 100% at concentrations of 6.3 and 12.5 μM, respectively. Azetidine and 2-azetidinone showed little activity on the tested algae. The results demonstrate that AZC selectively inhibits algal growth at low concentrations. The green algae C. vulgaris and Scenedesmus spp. were tolerant, whereas M. aeruginosa, A. affinis, and C. polykrikoides were relatively sensitive. Thus, extract and AZC, prepared from P. odoratum rhizomes, showed a potential as natural selective algicide for the control of harmful algae in laboratory assay.     

Physiological responses to flooding and light in two tree species native to the Amazonian floodplains

In Amazonian floodplains, plant survival is determined by adaptations and growth strategies to effectively capture sunlight and endure extended periods of waterlogging. By measuring gas exchange, quantum efficiency of photosystem 2 (PSII), and growth parameters, we investigated the combined effects of flooding gradients and light on two common evergreen floodplain tree species, the light-tolerant Cecropia latiloba and the shade-tolerant Pouteria glomerata. Individual plants were subjected to different combinations of light and flooding intensity in short-term and long-term experiments. Plants of C. latiloba lost all their leaves under total submersion treatments (plants flooded to apex and with reduced irradiance) and showed highest maximum assimilation rates (A_max) in not flooded, high light treatments (6.1 μmol CO₂ m⁻² s⁻¹). Individuals of P. glomerata showed similar patterns, with A_max increasing from 1.9 μmol CO₂ m⁻² s⁻¹ under total flooding to 7.1 μmol CO₂ m⁻² s⁻¹ in not flooded, high light treatments. During the long-term flooding experiment, quantum efficiency of PSII (F_v/F_m) of C. latiloba was not affected by partial flooding. In contrast, in P. glomerata F_v/F_m decreased to values below 0.73 after 120 days of total flooding. Moreover, total submergence led P. glomerata to reduce significantly light saturation point (LSP), as compared to C. latiloba. For both species morphological adjustments to long-term flooding, such as the production of adventitious roots, resulted in reduced total biomass, relative growth rate (RGR) and leaf mass ratio (LMR). Growth increase in C. latiloba seemed to be more limited by low-light than by flooding. Therefore, the predominant occurrence of this species is in open areas with high light intensities and high levels of inundation. In P. glomerata flooding induced high reductions of growth and photosynthesis, whereas light was not limiting. This species is more abundant in positions where irradiance is reduced and periods of submergence are slightly modest. We could show that the physiological requirements are directly responsible for the flooding (C. latiloba) and shade (P. glomerata) tolerance of the two species, which explains their local distribution in Amazonian floodplain forests.