Effects of irradiance and water flow on formation and growth of spongy and filamentous thalli of Codium fragile

Effects of irradiance and water flow on formation and growth of filamentous and spongy thalli of Codium fragile (Suringar) Hariot growing on vinylon threads were investigated at the laboratory culture. They showed clear differences in their irradiance and water flow requirements for their formation and growth. Spongy thalli were formed from the cultured filamentous thalli only at the high water flow velocity (10 cm s⁻¹). Number of the spongy thalli remarkably increased with increasing irradiance because those at 10, 50 and 100 μmol m⁻² s⁻¹ reached 0, 2 and 76 thalli m⁻¹, respectively, by 10 weeks of culture. In contrast, filamentous thalli were formed from the cultured spongy thalli at 0 and 3 cm s⁻¹, and difference in irradiance had no effect on their formation. Growth of the spongy thalli greatly accelerated under the combination of the high irradiance and high water velocity (200 μmol m⁻² s⁻¹ and 10 cm s⁻¹) because their relative growth rate in wet weight under the condition was two–four times higher than those at the other examined irradiances and water velocities. On the other hand, difference in water velocity had no effect on growth of the filamentous thalli under flowing water, and their growth decelerated at the high irradiance (200 μmol m⁻² s⁻¹). This demonstrates that water flow is a major factor controlling the formation of the spongy and filamentous thalli. The formation and growth of the spongy thalli surely occur under the combination of the high irradiance and fast flowing water. In contrast, the formation of the filamentous thalli occurs in the calm water, and their growth is inhibited under the high irradiance.     

Sex-specific light acclimation of Chara canescens (Charophyta)

Bisexual populations of the charophyte Chara canescens (Desv. et Loisel. in Loisel., 1810) containing male and female individuals are rarely found. Two experiments were carried out to study whether male and female algae from the same site exhibit different physiological capacities, especially with respect to light acclimation.Algae from two different shore levels and from laboratory cultures acclimated to six irradiance conditions (35–500 μmol photons m⁻² s⁻¹) were compared. Field measurements showed that both female and male algae of C. canescens are able to acclimate to daily changes in solar irradiance. The quantum yield of Photosystem II (PSII) decreased with increasing irradiance in the morning and increased with decreasing irradiance in the afternoon. Growth experiments showed increasing growth rates from 35 μmol photons m⁻² s⁻¹ (∼7 mg FW) up to 500 μmol photons m⁻² s⁻¹ (∼27 mg FW) in female and male C. canescens. The irradiance saturation point for photosynthesis (E_k) was about 140 μmol m⁻² s⁻¹ for both sexes within the whole range of acclimation irradiances. The maximum photosynthesis rate at saturating irradiances (P_max) of male algae was highest at E_k, whereas P_max of female algae was highest at 500 μmol photons m⁻² s⁻¹. The photosynthetic efficiency in the light-limited range (α) increased in female C. canescens and decreased in male C. canescens. The ratio of the non-photochemical quenching parameter (NPQ) to the relative electron transport rates rETR_(MT) increased in both sexes with irradiance, but showed a steeper increase in male than in female algae. Pigment analysis showed similar acclimation pattern for male and female C. canescens. Chl a/Chl b ratios of both sexes were constant over the whole range of E_g, whereas Chl a/carotenoid ratios in male and female C. canescens decreased from 70 μmol photons m⁻² s⁻¹ upwards. Pigment analysis pointed out that the carotenes α-, β- and γ-carotene were more prominent in male than in female algae.Our results indicate that female C. canescens are more efficient in light acclimation than male algae from the same site. Nevertheless, further investigations of bisexual C. canescens populations resolving CO₂-uptake mechanisms and/or genetic differences are needed.     

Growth of eight Gambierdiscus (Dinophyceae) species: Effects of temperature,salinity and irradiance

Little is known about how the growth of individual Gambierdiscus species responds to environmental factors. This study examined the effects of temperature (15–34 °C), salinity (15–41) and irradiance (2–664 μmol photons m⁻² s⁻¹) on growth of Gambierdiscus: G. australes, G. belizeanus, G. caribaeus, G. carolinianus, G. carpenteri, G. pacificus and G. ruetzleri and one putative new species, Gambierdiscus ribotype 2. Depending on species, temperatures where maximum growth occurred varied between 26.5 and 31.1 °C. The upper and lower thermal limits for all species were between 31–34 °C and 15–21 °C, respectively. The shapes of the temperature vs. growth curves indicated that even small differences of 1–2 °C notably affected growth potentials. Salinities where maximum growth occurred varied between 24.7 and 35, while the lowest salinities supporting growth ranged from <14 to 20.9. These data indicated that Gambierdiscus species are more tolerant of lower salinities than is generally appreciated. Growth of all species began to decline markedly as salinities exceed 35.1–39.4. The highest salinity tested in this study (41), however, was lethal to only one species, Gambierdiscus ribotype 2. The combined salinity data indicated that differences in salinity regimes may affect relative species abundances and distributions, particularly when salinities are <20 and >35. All eight Gambierdiscus species were adapted to relatively low light conditions, exhibiting growth maxima at 50–230 μmol photons m⁻² s⁻¹ and requiring only 6–17 μmol photons m⁻² s⁻¹ to maintain growth. These low light requirements indicate that Gambierdiscus growth can occur up to 150 m depth in tropical waters, with optimal light regimes often extending to 75 m. The combined temperature, salinity and light requirements of Gambierdiscus can be used to define latitudinal ranges and species-specific habitats, as well as to inform predictive models.     

Purification and characterization of yellow laccase from Trametes hirsuta MTCC-1171 and its application in synthesis of aromatic aldehydes

A yellow laccase from the culture filtrate of Trametes hirsuta MTCC-1171 has been purified. The purification methods involved concentration of the culture filtrate by ammonium sulphate precipitation and an anion exchange chromatography on diethylaminoethyl cellulose. The sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide gel electrophoresis gave single protein band indicating that the enzyme preparation was pure. The molecular mass of the enzyme determined from SDS-PAGE analysis was 55.0 kDa. Using 2,6-dimethoxyphenol, 2,2′[azino-bis-(3-ethylbonzthiazoline-6-sulphonic acid) diammonium salt] and 3,5-dimethoxy-4-hydroxybenzaldehyde azine as the substrates, the K_m, k_cat and k_cat/K_m values of the laccase were found to be 420 μM, 13.04 s⁻¹, 3.11 × 10⁴ M⁻¹ s⁻¹, 225 μM, 13.03 s⁻¹, 1.3 × 10⁵ M⁻¹ s⁻¹ and 100 μM, 13.04 s⁻¹, 5.8 × 10⁴ M⁻¹ s⁻¹, respectively. The pH and temperature optima were 4.5 and 60 °C, respectively while pH and temperature stabilities were pH 4.5 and 50 °C. The activation energy for thermal denaturation of the enzyme was 18.6 kJ/mol/K. The purified laccase has yellow colour and does not show absorption band around 610 nm like blue laccases. The purified laccase transforms toluene, 3-nitrotoluene, 4-nitrotoluene, 3-chlorotoluene, 4-chlorotoluene and 3,4-dimethoxytoluene to benzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 3-chlorobenzaldehyde, 4-chlorobenzaldehyde and 3,4-dimethoxybenzaldehyde in the absence of mediator molecules in high yields.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

The metabolic cost of bicarbonate use in the submerged plant Elodea nuttallii

The aquatic plant Elodea nuttallii (Planch.) St. John has been shown to express plasticity in the source of inorganic carbon it uses for photosynthesis. An investigation was undertaken to determine what effect the switch from CO₂ to HCO₃⁻ use had on the growth of E. nuttallii. Plants were grown under reduced CO₂ availability that favoured the switch, together with control plants (CO₂ at equilibrium with air) that continued to use CO₂ only. The extent to which both sets of plants could utilise HCO₃⁻ was determined (as the ratio of oxygen evolution at pH 9 and 6.5), and several measures of growth were made. Although reduced CO₂ availability produced an increase in HCO₃⁻ utilisation, no differences were found in the measured growth of the plants. Therefore, it was possible to estimate, from the difference between the estimated rate of photosynthesis of the plants utilising HCO₃⁻ and those using CO₂ only, the approximate cost of constructing, maintaining and running the bicarbonate utilisation mechanism in this species as 69 μmol photons m⁻² s⁻¹. This value can be used to estimate an irradiance of circa 80 μmol m⁻² s⁻¹ below which HCO₃⁻ use would not be expected in this species, an irradiance commonly experienced by submerged macrophytes in the field.     

Geosmin production and polyphasic characterization of Oscillatoria limosa Agardh ex Gomont isolated from the open canal of a large drinking water system in Tianjin City,China

Taste and odor (T & O) episodes always cause strong effects on drinking water supply system. Luanhe River diversion into Tianjin City in China is an important drinking water resource. Massive growth of a benthic filamentous cyanobacterium with geosmin production in the open canal caused a strong earthy odor episode in Tianjin. On the basis of the morphological and molecular identification of this cyanobacterium as Oscillatoria limosa Agardh ex Gomont, the genetic basis for geosmin biosynthesis and factors influencing growth and geosmin production of O. limosa CHAB 7000 were studied in this work. A 2268-bp open reading frame, encoding 755 amino acids, was amplified and characterized as the geosmin synthase gene (geo), followed by a cyclic nucleotide-binding protein gene (cnb). Phylogenetic analysis implied that the evolution of the geosmin genes in O. limosa CHAB 7000 might involve a horizontal gene transfer event. Examination on the growth and geosmin production of O. limosa CHAB 7000 at different light intensities showed that the maximum geosmin production was observed at 10 μmol photons m⁻² s⁻¹, while the optimum growth was at 60 μmol photons m⁻² s⁻¹. Under three temperature conditions (15 °C, 25 °C, and 35 °C), the maximum growth and geosmin production were observed at 25 °C. Most amounts of geosmin were retained in cells during the growth phase, but high temperature and low light intensity increased the release of geosmin into the medium, implying that O. limosa CHAB 7000 had a high potential harm for the release of geosmin from its cells at these adverse conditions.     

Modelling of growth and accumulation of carotenoids in Haematococcus pluvialis as a function of irradiance and nutrients supply

This paper analyzes the feasibility of the autotrophic production of vegetative cells of Haematococcus pluvialis under conditions resembling outdoors. The experimental design simulates in laboratory with artificial light an outdoors circadian cycle similar to solar illumination. The influence of the irradiance and nutrient concentration on the growth rate and carotenoids accumulation in batch cultures is studied. The cultures were not photoinhibited even under the maximum irradiance-level tested (2500 μE m⁻² s⁻¹). Growth was kept nutrient-limited by using nutrients concentration below the standard inorganic medium (10 mM nitrate). When no nutrient-limitation occurs, the growth rate and biomass productivity measured 0.57 day⁻¹ and 0.28 g L⁻¹ day⁻¹, respectively, were similar to the maximum values reported, regardless of the nutritional regime: autotrophic, mixotrophic or heterotrophic. On the other hand, carotenogenesis was only observed under nutrient-limiting conditions when the medium strength was reduced to 0.2- or 0.3-fold of the standard medium. On the other hand, carotenogenesis ceased under severe nutrient deprivation (i.e. nutrient strength of 0.1-fold of the standard medium). The growth rate and the carotenoids accumulation rate were demonstrated to be a function of the average irradiance inside the culture, and of the nutrient content of the medium. A mathematical model for the observed behaviour is proposed. This model was adequate to fit all the experimental data obtained. The values determined for the characteristics parameters are in agreement with those found by other authors. Therefore, the proposed model can be a useful tool for the design and management of Haematococcus cultures, and could allow improving the yield of this production process.     

Light acclimation of photosynthesis in three charophyte species

The main aim of this study was to investigate if the charophyte species Chara baltica, Chara canescens (two populations from the Baltic Sea (BS) and the Gulf of Korinth, Greece (GK)), and Lamprothamnium papulosum exhibit different acclimation capacities to irradiance. Growth, photosynthesis and pigment content were examined in the laboratory under six irradiance conditions (35–500 μmol photons m⁻² s⁻¹). Growth experiments showed increasing growth rates from 35 μmol photons m⁻² s⁻¹ (∼10 mg fresh weight (FW)) up to 70 μmol photons m⁻² s⁻¹ (∼20 mg FW) in C. baltica, from 35 μmol photons m⁻² s⁻¹ (∼15 mg FW) up to 380 μmol photons m⁻² s⁻¹ (∼145 mg FW) in C. canescens (BS), and up to the highest growth irradiance in algae of L. papulosum (35 μmol: ∼5 mg FW; 500 μmol: ∼20 mg FW). The species were tested for their ability to acclimate to different growth irradiances (E_g) by calculating P_max (maximum photosynthesis rate at saturating irradiances), α (the efficiency of light utilization at limiting irradiance), and E_k (the light saturation point of photosynthesis, P_max/α). All species exhibited increasing P_max with increasing E_g. Whereas both populations of C. canescens increased α with increasing E_g, L. papulosum and C. baltica did not acclimate α at all. E_k, the irradiance at which photosynthesis ceased to be light-limited, was constant for all Chara species within the range of irradiances tested. Chl a/Chl b ratios of all species were constant over the whole range of E_g. Chl a/carotenoid ratios were constant in C. baltica, whereas Chl a/carotenoid ratios in L. papulosum and C. canescens (BS) decreased from 250 and 70 μmol photons m⁻² s⁻¹ upwards, respectively. Pigmentation analysis showed that Chl a/carotenoid acclimation was mainly caused by species-specific capacity to raise the content of lutein and carotene (C. canescens (BS), C. canescens (GK)) and xanthophyll cycle pigments (XCP; L. papulosum). The non-photochemical quenching (NPQ) capacities of L. papulosum, C. canescens (BS), and C. canescens (GK) were dependent from preacclimation status of algae, whereas NPQ of C. baltica was independent from growth irradiance.Our results indicate that C. baltica and C. canescens (BS) were light saturated within the chosen irradiances, whereas C. canescens (GK) and L. papulosum did not reach their limits of high-light acclimation. The photosynthetic pigments lutein, α- and β-carotene are suggested to act as photo-protective pigments in L. papulosum and C. canescens.     

Differences in the photoacclimation and photoprotection exhibited by two species of the ciguatera causing dinoflagellate genus,Gambierdiscus

In culture, Gambierdiscus spp. have been shown to prefer irradiances that are relatively low (≤250 μmol photons m⁻² s⁻¹) versus those to which they are frequently exposed to in their natural environment (>500 μmol photons m⁻² s⁻¹). Although several behavioral strategies for coping with such irradiances have been suggested, it is unclear as to how these dinoflagellates do so on a physiological level. More specifically, how do long term exposures (30 days) affect cell size and cellular chlorophyll content, and what is the photosynthetic response to short term, high irradiance exposures (up to 1464 μmol photons m⁻² s⁻¹)? The results of this study reveal that cell size and chlorophyll content exhibited by G. carolinianus increased with acclimation to increasing photon flux density. Additionally, both G. carolinianus and G. silvae exhibited reduced photosynthetic efficiency when acclimated to increased photon flux density. Photosynthetic yield exhibited by G. silvae was greater than that for G. carolinianus across all acclimation irradiances. Although such differences were evident, both G. carolinianus and G. silvae appear to have adequate biochemical mechanisms to withstand exposure to irradiances exceeding 250 μmol photons m⁻² s⁻¹ for at least short periods of time following acclimation to irradiances of up to 150 μmol photons m⁻² s⁻¹.     

Evaluation of the effects of light intensity on growth of the benthic dinoflagellate Ostreopsis sp. 1 using a newly developed photoirradiation-culture system and a novel regression analytical method

Benthic dinoflagellates of the genus Ostreopsis are found all over the world in temperate, subtropical, and tropical coastal regions. Our recent studies revealed that a putative “cryptic” species of Ostreopsis ovata is present widely along Japanese coasts. This organism, Ostreopsis sp. 1, possesses palytoxin analogs and thus its toxic blooms may be responsible for potential toxification of marine organisms. To evaluate the bloom dynamics of Ostreopsis sp. 1, the present study examined the growth responses of Ostreopsis sp. 1 strain s0716 to various light intensities (photon flux densities: μmol photons m⁻² s⁻¹) using a newly devised photoirradiation-culture system. This novel system has white light-emitting diodes (LEDs) capable of more closely simulating the wavelength spectrum of light entering the oceanic water column than do fluorescent tubes and halogen lamps. In this system, the light intensity of the white LEDs was reduced through two polarizing filters by varying the rotation angles of the filters. Thereby, the new system was capable of culturing microalgae under well-controlled light intensity conditions. Ostreopsis sp. 1 grew proportionally when light intensity was increased from 49.5 to 199 μmol photons m⁻² s⁻¹, but its growth appeared to be inhibited slightly at ≥263 μmol photons m⁻² s⁻¹. The relationship between observed growth rates and light intensity was calculated at R > 0.99 (P < 0.01) using a regression analysis with a modified equation of the photosynthesis-light intensity (P-L) model. The equation determined the critical light intensities for growth of Ostreopsis sp. 1 and the organism's growth potential as follows: (1) the threshold light intensity for growth: 29.8 μmol photons m⁻² s⁻¹; (2) the optimum light intensity (L_m) giving the maximum growth rate (μ_max = 0.659 divisions day⁻¹): 196 μmol photons m⁻² s⁻¹; (3) the optimum light intensity range (L_opt) giving ≥95% μ_max: 130–330 μmol photons m⁻² s⁻¹; (4) the semi-optimum range (L_sopt) giving ≥80% μ_max: 90 to over 460 μmol photons m⁻² s⁻¹. The L_sopt represents 4.5–23% ambient light intensity present in surface waters off of a temperate region of the Japanese coast, Tosa Bay; putatively, this semi-optimum range of light intensity appears at depth of 12.9–27.8 m. Considering these issues, our data indicate that Ostreopsis sp. 1 in coastal environments may form blooms at ca. ∼28 m depth in regions along Japanese coasts.     

Accumulation of phycocyanin in heterotrophic and mixotrophic cultures of the acidophilic red alga Galdieria sulphuraria

The relationship between light intensity, nitrogen availability and pigmentation was investigated in mixotrophic and heterotrophic cultures of the unicellular red alga Galdieria sulphuraria 074G, a potential host for production of the blue pigment, phycocyanin (PC). During the exponential growth phase of batch cultures, G. sulphuraria 074G contained 2–4 mg phycocyanin per g dry weight. In carbon-limited and nitrogen-sufficient batch cultures grown in darkness, this value increased to 8–12 mg g⁻¹ dry weight during the stationary phase, whereas the phycocyanin content in nitrogen-deficient cells decreased to values below 1 mg g⁻¹ dry weight during stationary phase. Light intensities between 0 and 100 μmol photons m⁻² s⁻¹ had no influence on phycocyanin accumulation in mixotrophic cultures grown on glucose or fructose, while light stimulated phycocyanin synthesis in cultures grown on glycerol, in which the phycocyanin content in stationary phase was increased from 10 mg g⁻¹ dry weight in darkness to 20 mg g⁻¹ dry weight at a light intensity of 80 μmol photons m⁻² s⁻¹. At higher light intensities, less phycocyanin accumulated than at lower intensities, irrespective of the carbon substrate used. In carbon-limited continuous flow cultures grown on glucose or glycerol at a dilution rate of 0.63 day⁻¹, corresponding to 50% of the maximum specific growth rate, the highest steady-state phycocyanin content of 15–28 mg g⁻¹ dry weight was found at 65 μmol photons m⁻² s⁻¹. In contrast to the apparent glucose repression of light-induced PC synthesis observed in batch cultures, no glucose repression of the light stimulation was observed in continuous flow cultures because the glucose concentration in the culture supernatant always remained at limiting levels. Despite the fact that G. sulphuraria 074G contains less phycocyanin than some other microalgae and cyanobacteria, the ability of G. sulphuraria 074G to grow and synthesize phycocyanin in heterotrophic or mixotrophic cultures makes it an interesting alternative to the cyanobacterium, Spirulina platensis presently used for synthesis of phycocyanin.     

The effects of light intensity on the growth of Japanese Gambierdiscus spp. (Dinophyceae)

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (L_max) and the semi-optimum light intensity range (L_s-opt) that resulted in the maximum growth rate (μ_max) and ≥80% μ _max values of the four species/phylotypes, respectively, were as follows: (1) the L_max and L_s-opt of G. australes were 208 μmol photons m⁻² s⁻¹ and 91–422 μmol photons m⁻² s⁻¹, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m⁻² s⁻¹, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m⁻² s⁻¹, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m⁻² s⁻¹, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m⁻² s⁻¹ to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m⁻¹. The values 1700 μmol photons m⁻² s⁻¹, 500 μmol photons m⁻² s⁻¹, and 200 μmol photons m⁻² s⁻¹ were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of L_max and L_s-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.     

Growth and domoic acid content of Pseudo-nitzschia australis isolated from northwestern Baja California,Mexico, cultured under batch conditions at different temperatures and two Si:NO3 ratios

Domoic acid (DA) poisoning in the southern part of the California Current System has been associated typically with blooms of Pseudo-nitzschia australis. The environmental variables that promote growth and DA production in the Mexican part of this system have not been identified. The present study investigated the effect of temperature and two nutrient ratios on the growth characteristics and DA content of two (BTS-1, BTS-2) P. australis strains isolated from the Pacific coast of northern Baja California peninsula, México. Of the different temperatures assayed (10, 12, 14, 15, 18 and 20 °C), the maximum cell abundance was detected at 12 °C for BTS-2 and 14 °C for BTS-1. The highest maximum specific growth rate (1.69 day⁻¹) was measured at 15 °C for BTS-2. With the exception of cells maintained at 15 °C, growth characteristics were similar in P. australis cultured in a high Si:NO₃ (2.5) or low Si:NO₃ (0.5) ratio at each temperature. Dissolved (dDA) and cellular (cDA) DA content measured at the stationary phase of growth was similar in cells cultivated at the different temperatures. No difference in cDA (between 0.11 and 1.87 pg DA cell⁻¹) was observed in cells cultivated at the two nutrient ratios. To evaluate if P. australis accumulates DA (cDA + dDA) at different stages of the culture and not only during the stationary phase of growth, the BTS-1 strain was cultivated at 14 °C and the content of this toxin was measured during culture development. The cultures were maintained at high (HL; 200 μmol quanta m⁻² s⁻¹) and low light (LL; 30 μmol quanta m⁻² s⁻¹) and in the two nutrient ratios to evaluate the effect of these variables on DA content. The photosynthetic performance and pigment concentration were measured as indicators of the physiological condition of the cells. cDA was detected in all culture conditions and during the different stages of growth. The highest DA content was measured during the lag phase of growth and it was present mainly in the medium (dDA = 70.83 pg DA cell⁻¹). Cells cultivated at HL produced more DA than LL cultured cells. P. australis cultured in HL presented lower photosynthetic rates than LL cells and had similar concentrations of photoprotective pigments and the highest maximum photosynthetic rates were detected during the lag phase of growth in all culture conditions. The results demonstrate that P. australis from northern Baja California peninsula presents a narrow temperature range for optimal growth under batch culture conditions. P. australis produce DA at different stages of growth, and DA content was related to the light intensity at which the cells were cultivated.     

Successful storage of protocorm-like bodies of hybrid Cymbidium (Orchidaceae) under low temperature conditions

Low temperatures result in lower metabolic cellular activity, thus slowing down cell division and growth. This is advantageous where a plant scientist might seek to store important germplasm without the risks associated with low temperature storage. In this study, two cold temperatures above freezing, namely 4 and 10 °C, were tested to assess for how long PLBs could be preserved without a significant loss in regeneration ability (i.e., the ability to form neo-PLBs). Control treatments were cultured at 25 °C on Teixeira Cymbidium (TC) medium at a 16-h photoperiod at a photosynthetic photon flux density (PPFD) of 45 μmol m⁻² s⁻¹. For the cold treatments, each was replicated in the dark and at low light intensity (12-h photoperiod and a PPFD of 10 μmol m⁻² s⁻¹). All cultures were sub-cultured six times onto fresh medium every 60 days, for approximately 1 year. On the 7th subculture, all neo-PLBs were prepared uniformly and replated onto standard TC medium under light conditions described above for the control. 45 days after the 7th subculture and just before subcultures 1–6, the number of neo-PLBs per half-PLB was measured. The number of neo-PLBs that formed under different treatments depended strongly on the temperature and light conditions with most neo-PLBs forming under control conditions, although that number dropped significantly as the temperature was dropped to 10 °C and then even more to 4 °C, the same trend being observed when explants were cultured and subcultured under dim light, with organogenesis being more strongly negatively influenced in darkness. For all low-temperature treatments, as well as the dimmed light and darkness treatments, the number of neo-PLBs increased significantly when recultured, on the 7th subculture, onto control TC medium under control environmental conditions, almost as high as the control values. In contrast, the control values decreased, with significantly fewer neo-PLBs by the 7th subculture relative to the control, indicating that new PLBs should be induced from shoot cultures at least once a year to maintain their vitality.     

Allelopathic inhibition of phytoplankton by exudates from Stratiotes aloides

The allelopathic potential of exudates from the aquatic macrophyte Stratiotes aloides on the growth of phytoplankton was investigated. A selection of phytoplankton species, occurring in habitats similar to that of Stratiotes, was used: two cyanobacterial strains (toxic and non-toxic Microcystis aeruginosa), one green alga (Scenedesmus obliquus) and one eustigmatophyte (Nannochloropsis limnetica). The results indicate allelopathic effects of Stratiotes on phytoplankton in six of the eight cases, expressed in an extended duration of the initial biovolume doubling time. The overall inhibitory effect (8–51%) was strain-specific for the two cyanobacteria. We also studied the effect of irradiance on the allelopathic potential of exudates from Stratiotes. Irradiance influenced the response of Scenedesmus only. The inhibitory effect of Stratiotes exudates on the growth of this green alga was stronger at 35 μmol m⁻² s⁻¹ than at 105 μmol m⁻² s⁻¹. We conclude that Stratiotes has allelopathic effects on phytoplankton, and that irradiance can, but does not always determine the extent of the allelopathic inhibition. In our experiments, the sensitivity of cyanobacteria to Stratiotes exudates was not higher than for other phytoplankton strains, but within cyanobacteria, the toxic strain was more sensitive than the non-toxic one.     

The dinoflagellate Akashiwo sanguinea will benefit from future climate change: The interactive effects of ocean acidification,warming and high irradiance on photophysiology and hemolytic activity

Due to global climate change, marine phytoplankton will likely experience low pH (ocean acidification), high temperatures and high irradiance in the future. Here, this work report the results of a batch culture experiment conducted to study the interactive effects of elevated CO₂, increased temperature and high irradiance on the harmful dinoflagellate Akashiwo sanguinea, isolated at Dongtou Island, Eastern China Sea. The A. sanguinea cells were acclimated in high CO₂ condition for about three months before testing the responses of cells to a full factorial matrix experimentation during a 7-day period. This study measured the variation in physiological parameters and hemolytic activity in 8 treatments, representing full factorial combinations of 2 levels each of exposure to CO₂ (400 and 1000 μatm), temperature (20 and 28 °C) and irradiance (50 and 200 μmol photons m⁻² s⁻¹). Sustained growth of A. sanguinea occurred in all treatments, but high CO₂ (HC) stimulated faster growth than low CO₂ (LC). The pigments (chlorophyll a and carotenoid) decreased in all HC treatments. The quantum yield (F_v/F_m) declined slightly in all high-temperature (HT) treatments. High irradiance (HL) induced the accumulation of ultraviolet-absorbing compounds (UV_abc) irrespective of temperature and CO₂. The hemolytic activity in the LC treatments, however, declined when exposed to HT and HL, but HC alleviated the adverse effects of HT and HL on hemolytic activity. All HC and HL conditions and the combinations of high temperature*high light (HTHL) and high CO₂*high temperature*high light (HCHTHL) positively affected the growth in comparison to the low CO₂*low temperature*low light (LCLTLL) treatment. High temperature (HT), high light (HL) and a combination of HT*HL, however, negatively impacted hemolytic activity. CO₂ was the main factor that affected the growth and hemolytic activity. There were no significant interactive effects of CO₂*temperature*irradiance on growth, pigment, F_v/F_m or hemolytic activity, but there were effects on P_m, α, and E_k. If these results are extrapolated to the natural environment, it can be hypothesized that A. sanguinea cells will benefit from the combination of ocean acidification, warming, and high irradiance that are likely to occur under future climate change. It is assumed that faster growth and higher hemolytic activity and UV_abc of this species will occur under future conditions compared with those the current CO₂ (400 μatm) and temperature (20 °C) conditions.     

Effects of intraspecific competition on growth and photosynthesis of Atriplex prostrata

We investigated the effect of intraspecific competition on growth parameters and photosynthesis of the salt marsh species Atriplex prostrata Boucher in order to distinguish the effects of density-dependent growth inhibition from salt stress. High plant density caused a reduction of 30% in height, 82% in stem dry mass, 80% in leaf dry mass, and 95% in root dry mass. High density also induced a pronounced 72% reduction in leaf area, 29% decrease in length of mature internodes and 50% decline in net photosynthetic rate. The alteration of net photosynthesis paralleled growth inhibition, decreasing from 7.6 ± 0.9 μmol CO₂ m⁻² s⁻¹ at low density to 3.5 ± 0.4 μmol CO₂ m⁻² s⁻¹ at high density, indicating growth inhibition caused by intraspecific competition is mainly due to a decline in net photosynthesis rate. Plants grown at high density also exhibited a reduction in stomatal conductance from 0.7 ± 0.1 mol H₂O m⁻² s⁻¹ at low density to 0.3 ± 0.1 mol H₂O m⁻² s⁻¹ at high density and a reduction in transpiration rate from 6.0 ± 0.3 mmol H₂O m⁻² s⁻¹ at low density to 4.3 ± 0.3 mmol H₂O m⁻² s⁻¹ at high density. Biomass production was inhibited by an increase in plant density, which reduced the rate of photosynthesis, stomatal conductance and leaf area of plants.     

The effect of water temperature and velocity on barnacle growth: Quantifying the impact of multiple environmental stressors

Organisms employ a wide array of physiological and behavioral responses in an effort to endure stressful environmental conditions. For many marine invertebrates, physiological and/or behavioral performance is dependent on physical conditions in the fluid environment. Although factors such as water temperature and velocity can elicit changes in respiration and feeding, the manner in which these processes integrate to shape growth remains unclear. In a growth experiment, juvenile barnacles (Balanus glandula) were raised in dockside, once-through flow chambers at water velocities of 2 versus 19 cm s⁻¹ and temperatures of 11.5 versus 14 °C. Over 37 days, growth rates (i.e., shell basal area) increased with faster water velocities and higher temperatures. Barnacles at high flows had shorter feeding appendages (i.e., cirri), suggesting that growth patterns are unlikely related to plastic responses in cirral length. A separate experiment in the field confirmed patterns of temperature- and flow-dependent growth over 41 days. Outplanted juvenile barnacles exposed to the faster water velocities (32±1 and 34±1 cm s⁻¹; mean±SE) and warm temperatures (16.81±0.05 °C) experienced higher growth compared to individuals at low velocities (1±1 cm s⁻¹) and temperatures (13.67±0.02 °C). Growth data were consistent with estimates from a simple energy budget model based on previously measured feeding and respiration response curves that predicted peak growth at moderate temperatures (15 °C) and velocities (20–30 cm s⁻¹). Low growth is expected at both low and high velocities due to lower encounter rates with suspended food particles and lower capture efficiencies respectively. At high temperatures, growth is likely limited by high metabolic costs, whereas slow growth at low temperatures may be a consequence of low oxygen availability and/or slow cirral beating and low feeding rates. Moreover, these results advocate for approaches that consider the combined effects of multiple stressors and suggest that both increases and decreases in temperature or flow impact barnacle growth, but through different physiological and behavioral mechanisms.     

Oxygen enhances the recovery of Potamogeton maackianus from prolonged exposure to very low irradiance

Recovery ability in relation to carbohydrate content of Potamogeton maackianus growing in two dissolved oxygen concentrations (8 and 2 mg L⁻¹) was investigated during 28 days exposure to very low irradiance (about 0.06 μmol m⁻² s⁻¹). Plant weight remained relatively constant (0.19 g dry wt plant⁻¹) within the initial 21 days in the high oxygen treatment, but decreased to 0.14 g dry wt plant⁻¹ at the end of the experiment. In low oxygen environments, plant weight was similar within the initial 14 days, but decreased to 0.08 g dry wt plant⁻¹ at 21 day. During the experimental period, both soluble sugar and starch contents in shoots decreased with time. Compared to high oxygen treatment, plants in the low oxygen treatment depleted starch more quickly (25 versus 18 mg g⁻¹ at 28 day) but remained a relatively high soluble sugar content (0.9 versus 1.8 mg g⁻¹ at 28 day). After recovery in high light and high dissolved oxygen conditions for 1 week, plant growth rate, new branch number, stem elongation rate and leaf recruitment number were significantly higher in high oxygen than in the low oxygen treatments. These data suggest that the ability of the plant to recover from prolonged exposure to very low irradiance is related to the depletion level of carbohydrate stored in plant tissues, which is regulated by oxygen availability in the water.