Vertical structure and photosynthetic activity of Lake Shira phytoplankton

This study was conducted to analyse vertical dynamics of phytoplankton distribution in Shira Lake during the summer stratification regime. From late June to September phytoplankton in Shira Lake were stratified with the maximum in the lower part of the thermocline, at a depth of 8–12 m, with a chlorophyll concentration up to 23 g and biomass up to 5 mg l^–1. Maxima of chlorophyll and biomass of cyanobacteria and green algae were in different layers. From June to September a major part of chlorophyll a was in green algae, while under ice – in cyanobacteria. The variable fluorescence proves high photosynthetic activity of algae in the depth assemblage. Epifluorescent analysis disclosed that additional light-harvesting pigments were better developed in cells from the depth maximum. The maximum of gross primary production calculated from fluorescence corresponded to the depth maximum of phytoplankton. Primary production over a season was 2.7 gO₂ m^–2. Formation mechanisms of the depth maximum of phytoplankton are discussed in this paper.     

Diel periodicity in dark uptake of ammonium by natural populations of marine phytoplankton

We discovered the phenomenon that dark uptake of ammonium increasesat night and maximizes around midnight. The maximum values atmidnight are 2 or 3 times higher than the values in the daytime.     

Fatty acid composition in photosynthetic products of natural phytoplankton population in Lake Biwa, Japan

Fatty acid composition of phytoplankton photosynthetic productswas determined by a ¹³C tracer and gas chromatography-mass spectrometry(¹³C-GC-MS) method from August 1985 to June 1986 in Lake Biwa,Japan. The total fatty acid production rate varied from 2.8to 10.9 µg C l^–1 day^–1 at the water surfaceand accounted for 9.1–30% of photosynthetic productionof particulate organic carbon. A high contribution of fattyacid to the particulate organic carbon production rate was noticedduring winter time, and an increase in the fatty acid contributionresulted in an increase in the C/N value in the photosyntheticproducts. The fatty acid composition varied throughout the year,mainly depending on the seasonal change in the dominant phytoplanktonspecies. The contribution of polyunsaturated fatty acids tototal fatty acids was low during the summer period, probablydue to nitrogen limitation of phytoplankton growth.     

The effect of long wave ultraviolet radiation (UV-A) on the photosynthetic activity of natural population of freshwater phytoplankton

The effect of ultraviolet radiation on diel changes and depth profiles of phytoplankton photosynthesis was studied in four temperate freshwater lakes. Photosynthetic oxygen production was determined by incubating lake water in light and dark bottles under various weather conditions. Half the light bottles were wrapped with sheets of vinyl chloride film to exclude light with wavelengths shorter than 400 nm. The inhibition of photosynthesis due to UV-A (320–400 nm) was observed during most of the daytime and was very strong around noon on both sunny and cloudy days. On sunny days, when the surface waters of the highly eutrophic Lake Suwa and Senzoku Pond were dominated by denseMicrocystis populations, cumulative daily production at the surface, estimated from the incubation of bottles from which UV-A was excluded by the vinyl film, were about double the rates obtained from glass bottles in which UV-A was present. The UV-A inhibition was detected from the surface toca 20 cm depth in hypereutrophic lakes and at depths greater than 50 cm in mesotrophic lakes. Analysis of the photosynthesis-irradiance (P-I) relationship obtained in the present study shows β, a parameter that describes photo-inhibition, is higher in the presence of UV-A than in its absence. This indicates that UV-A is the major cause of photo-inhibition of phytoplankton photosynthesis.     

Inhibition of cyanobacterial photosynthetic activity by natural ketones

Microbial volatiles have a significant impact on the physiological functions of prokaryotic and eukaryotic organisms. Various ketones are present in volatile mixtures produced by plants, bacteria, and fungi. Our earlier results demonstrated the inhibitory effects of soil bacteria volatiles, including ketones, on cyanobacteria. In this work, we thoroughly examined the natural ketones, 2‐nonanone and 2‐undecanone to determine their influence on the photosynthetic activity in Synechococcus sp. PCC 7942. We observed for the first time that the ketones strongly inhibit electron transport through PSII in cyanobacteria cells in vivo. The addition of ketones decreases the quantum yield of primary PSII photoreactions and changes the PSII chlorophyll fluorescence induction curves. There are clear indications that the ketones inhibit electron transfer from Q_A to Q_B, electron transport at the donor side of PSII. The ketones can also modify the process of energy transfer from the antenna complex to the PSII reaction center and, by this means, increase both chlorophyll fluorescence quantum yield and the chlorophyll excited state lifetime. At the highest tested concentration (5 mM) 2‐nonanone also induced chlorophyll release from Synechococcus cells that strongly indicates the possible role of the ketones as detergents.     

Patterns of dark14CO2 incorporation by natural marine phytoplankton communities

The rates of dark¹⁴CO₂ fixation by natural phytoplankton communities growing in eutrophic and oligotrophic waters were studied with short-term in situ experiments. Three aspects were investigated: (1) the time course incorporation of¹⁴CO₂ in darkness, (2) the depth variability in dark¹⁴CO₂ fixation, and (3) the variability in¹⁴CO₂ fixation within a year. The highest dark¹⁴CO₂ incorporation rates were observed during the first interval of incubation (20 min) after which they approached a constant rate with time. The observed differences in dark¹⁴CO₂ fixation rates between populations from different depths were associated with differences in species composition as well as with physiological differences caused by exposure to different illumination conditions prior to their exposure to darkness. Autocorrelation coefficients were computed for the analysis of variability of dark¹⁴CO₂ fixation rates within a year. It was suggested that dark¹⁴CO₂ incorporation might be a periodic phenomenon depending mainly on the productive capacity of the phytoplankton community.     

Influence of environemntal factors on phytoplankton photosynthetic activity in the Volga River reservoirs

The relation of the photosynthetic activity of phytoplankton biomass in the Volga River reservoirs to environmental factors has been analyzed. It is revealed that values of A/B and P/B coefficients depend to the largest extent on the content of total nitrogen, as well as on the temperature and illumination, the factors integrating the effect of geographical zonality. Among the proper phytoplankton parameters, its production capabilities are determined by the taxonomic composition, cenotic diversity and cell sizes, biomass, and physiological state of populations. Maximal values of A/B and P/B coefficients are characteristic of the algal communities with prevailing small-celled green, dinophytic, and cryptophytic algae.     

Effects of simulated upwelling and oligotrophy on chemostat-grown natural marine phytoplankton assemblages

Natural phytoplankton assemblages from the Scripps Pier were grown in two chemostats under conditions that simulated two rates of upwelling followed by oligotrophic conditions. At a moderate upwelling rate (D = 0.3·day^?1) centric diatoms were selected, while at a low rate (D = 0.1·day^?1) a mixture of species dominated. Pumping of low-nutrient water (oligotrophy) resulted in a mixture of species at both rates. Upwelling at a high rate decreased diversity of the crop as compared with the low rate or oligotrophy. These results are compared with those of others who have subjected natural assemblages to continuous culture.     

Response to polychlorinated biphenyls of marine phytoplankton isolates cultured under natural conditions.

Polychlorinated biphenyls (PCB) at a concentration of 10 mug/liter substantially but temporarily suppressed the growth rate and photosynthesis of two species of Thalassiosira recently isolated from Long Island Sound and grown in dialysis membrane bags suspended in the tidal channel of an estuarine marsh. Inhibition of carbon fixation was apparently due to reduced levels of chlorophyll a per PCB-treated cell, but no significant loss of function per unit of existing chlorophyll a was observed. Cell concentrations in all size classes (3.2- to 18.6-mum-equivalent spherical diameters) were markedly lower in PCB-treated cultures, with toal biomass equaling only 30% of that in control cultures throughout the experiment.     

A method for determining alkaline phosphatase activity in marine phytoplankton using spectrofluorometry

A method for determining relative percent intensity alkaline phosphatase activity (APA) using enzyme labeled fluorescence coupled with spectrofluorometry is presented. Compared to traditional microscopy and flow cytometry, we increase statistical power and reduce sample-handling issues. Combined with a biological standard, our method can quantify APA of natural plankton assemblages.     

海洋浮游藻类细胞质膜氧化还原活性与细胞外CA活性的关系（简报）

Exofacial ferricyanide reduction at the plasma membrane of intact cells, and the link between plasma membrane redox activity, inorganic carbon status of the cells and extracellular carbonic anhydrase (CAext) activity were assayed using 10 marine phytoplankton species. In species Chaetocceros compressus, Cocolithus pelagicus and Gephyrocapsa ocetanica with no extracellular CA activity under carbon-limited or carbon-replete conditions, barely detectable ferricyanide reduction was observed. Species Skeletonema costatum, Melosira sp., Thalassiosira rotula, Thalassiosira weisflogi and Pleurochrysis carterae in which extracellular CA activity was only detected under carbon-limited conditions showed high rates of exofacial ferricyanide reduction. Western blotting and immunolocalization showed the presence of enzyme protein under carbon-limited and replete conditions at the cell surface, even though the CA activity could only detected when inorganic carbon was limiting, which suggests that the development of extracellular CA in response to carbon limitation is an activation of a preexisting protein rather than de novo synthesis. The results suggest that inorganic carbon limitation in the light increases plasma membrane redox activity and promotes proton extrusion, which result in the protonation and activation of the extracellular CA.     

Cell-specific beta-N-acetylglucosaminidase activity in cultures and field populations of eukaryotic marine phytoplankton.

It is widely appreciated that eukaryotic marine phytoplankton can hydrolyze a variety of compounds within the dissolved organic matter (DOM) pool in marine environments. Herein, cultures and field populations of marine phytoplankton were assayed for beta-N-acetylglucosaminidase activity, a terminal enzyme of chitin degradation. A traditional bulk assay, which can assess hydrolytic rate, but is not cell-specific, was complemented with a cell-specific assay that images the activity associated with single cells using an enzyme labeled fluorescence (ELF) substrate. beta-N-acetylglucosaminidase activity was widespread across various taxa of marine phytoplankton, and activity was observed both under controlled culture conditions and in field populations. The number of cells with enzyme activity varied with the nutritional physiology of the test species in three of the 17 cultures tested. In these three cases the number of cells with activity in the low nutrient medium was higher than in nutrient replete medium. Taken together, these data suggest that a broad group of marine phytoplankton may be a relevant part of chitin-like DOM degradation and should be incorporated into conceptual models of chitin cycling in marine systems.     

Effects of ethephon on aging and photosynthetic activity in isolated chloroplasts

Chloroplasts, isolated from the primary leaves of 7-day-old seedlings, were incubated in vitro at 25°C with 2-chloroethylphosphonic acid (ethephon) under light (0.16 milliwatts per square centimeter) and dark conditions. Ethephon at 1 micromolar (0.1445 ppm), 0.1 and 1 millimolar, or 5 microliters ethylene promoted the deterioration of chloroplasts, increased proteolysis, and reduced the chlorophyll content and PSI and PSII during 72 hours under both light and dark conditions. The decline in PSI and PSII occurred prior to a measurable loss of chlorophyll. The loss of photosynthetic activity affected by ethephon was initiated prior to 12 hours of incubation. After 24 hours in light, 0.1 millimolar (1.445 ppm) epthephon significantly reduced PSI and PSII and promoted the total free amino acid liberation in isolated chloroplasts. In darkness the rate of loss of PSI activity was about 50% of that in light. After 24 hours, in light at 1 millimolar epthephon, PSII activity was 55% of the control, yet nearly 90% of the chlorophyll remained, which indicates that the loss of thylakoid integrity was promoted by ethephon. Ethylene injected in the chloroplast medium at 5 microliters (0.22 micromolar per milliliter) reduced PSI by nearly 50% of the initial in 12 hours. In leaf sections floated in 5 microliters per milliliter suspension medium, a 36% loss of chlorophyll of the control in 36 hours was observed. Cycloheximide at 0.5 millimolar masked the effect of 1 millimolar ethephon and maintained the initial chlorophyll content during the 72 hour period.     

Carbon isotope ratio and photosynthetic activity of phytoplankton in the eutrophic Mikawa Bay,Japan

Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural carbon isotope ratio (δ ¹³C) and short-term carbon uptake rates (¹³C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates, which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ ¹³C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction (−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more negativeδ ¹³C values (−22 to −18‰). Highδ ¹³C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the nannoplankton fractions with higher POC values have relatively lowδ ¹³C values.     

Temporal stability of marine phytoplankton in a subtropical coastal environment

We investigated the temporal stability of phytoplankton at a subtropical coastal site for 9 months by conducting chlorophyll and flow cytometric measurements at relatively high frequency (roughly at 2–5 day interval). Phytoplankton cells were grouped based on their sizes obtained from flow cytometric signals. We also conducted dilution experiments to estimate the growth and grazing mortality rates of different phytoplankton groups to assess whether the temporal stability of phytoplankton abundances was related with phytoplankton growth/grazing rates. Based on size-fractionated chlorophyll measurements, there was some indication that smaller phytoplankton cells were more stable than larger ones. However, by cytometric counting, there was no evidence for greater stability in small cells. Synechococcus, which had the lowest stability and dominated the <1 μm size class, showed a strong seasonal cycle that was highly dependent on temperature whereas eukaryotes did not have evident seasonal cycles. In general, biomass of a phytoplankton group consisting of several size classes was more stable than that of its sub component, consistent with the hypothesis that higher diversity leads to higher stability, probably related with the effect of statistical averaging (portfolio effect). Stability of heterotrophic bacteria was much higher than that of phytoplankton, leading to the speculation that bacteria were more diverse than phytoplankton. Phytoplankton stability was not related with their growth or grazing mortality rates. Our study suggests that species diversity should be taken into account when considering the temporal stability of phytoplankton.     

Spatial and temporal variation of photosynthetic parameters in natural phytoplankton assemblages in the Beaufort Sea, Canadian Arctic

During summer 2008, as part of the Circumpolar Flaw Lead system study, we measured phytoplankton photosynthetic parameters to understand regional patterns in primary productivity, including the degree and timescale of photoacclimation and how variability in environmental conditions influences this response. Photosynthesis–irradiance measurements were taken at 15 sites primarily from the depth of the subsurface chlorophyll a (Chl a) maximum (SCM) within the Beaufort Sea flaw lead polynya. The physiological response of phytoplankton to a range of light levels was used to assess maximum rates of carbon (C) fixation (P _m^*), photosynthetic efficiency (α ^*), photoacclimation (E _k), and photoinhibition (β ^*). SCM samples taken along a transect from under ice into open water exhibited a >3-fold increase in α ^* and P _m^*, showing these parameters can vary substantially over relatively small spatial scales, primarily in response to changes in the ambient light field. Algae were able to maintain relatively high rates of C fixation despite low light at the SCM, particularly in the large (>5 μm) size fraction at open water sites. This may substantially impact biogenic C drawdown if species composition shifts in response to future climate change. Our results suggest that phytoplankton in this region are well acclimated to existing environmental conditions, including sea ice cover, low light, and nutrient pulses. Furthermore, this photoacclimatory response can be rapid and keep pace with a developing SCM, as phytoplankton maintain photosynthetic rates and efficiencies in a narrow “shade-acclimated” range.     

Enzymatic degradation of chlorophyll a by marine phytoplankton in vitro

The enzymatic degradation of chlorophyll a and the formation of chlorophyllide a, phaeophytin a, and phaeophorbide a were detected in vitro in several species of marine phytoplankton. Loss of phytol and Mg²⁺ were found to be catalysed by chlorophyllase and a magnesium-releasing enzyme, respectively. The activities of the two enzymes could be distinguished from each other by inhibiting with Mg²⁺ and/or p-chloromercurobenzoate. Both enzymes are activated by cell disintegration. Degradation products were not detected spectrophotometrically in vivo. Additionally, in some species, chlorophyll a was degraded to products which do not absorb visible light.     

Extracellular endoglucanase activity by a novel bacterium isolated from marine shipworm

An extracellular enzyme preparation from shipworm bacterium cultures dramatically increased reducing sugar content of carboxymethylcellulose (CMC3), but did not solubilize sugar from particulate cellulose. The preparation degraded cellodextrins larger than cellotriose (G3). Only interior cellodextrin chain linkages were cleaved and the center-most bond of cellohexaose (G6) was preferentially cleaved. Activity maxima were observed at 60 degrees C and between pH 5.0 and 7.0. The activity was resistant to protease treatment and little loss of activity was observed after 14 d at 25 degrees C.     

Antitumor activity of the marine natural product dibromophakellstatin in vitro

The pyrrole-imidazole alkaloid rac-dibromophakellstatin displayed selective antitumor activity in vitro when tested in 36 cell lines in a cell survival and proliferation assay. The ovarian cancer cell line OVXF 899L proved to be most sensitive (0.60 microM, IC50), followed by the glioblastoma cell line CNXF 498NL (0.93 microM), the non-small lung cancer cell line LXF 529L (0.96 microM), and the uterus cancer cell line UXF 1138L (1.21 microM). The selectivity profile of rac-dibromophakellstatin may be indicative for a novel mechanism of action. Separation of the enantiomers on a chiral HPLC column revealed that only the naturally occurring (-)-dibromophakellstatin is antitumor active. Debromination of the pyrrole moiety leads to complete loss of activity.     

Induced defences in marine and freshwater phytoplankton: a review

Many organisms have developed defences to avoid predation by species at higher trophic levels. The capability of primary producers to defend themselves against herbivores affects their own survival, can modulate the strength of trophic cascades and changes rates of competitive exclusion in aquatic communities. Algal species are highly flexible in their morphology, growth form, biochemical composition and production of toxic and deterrent compounds. Several of these variable traits in phytoplankton have been interpreted as defence mechanisms against grazing. Zooplankton feed with differing success on various phytoplankton species, depending primarily on size, shape, cell wall structure and the production of toxins and deterrents. Chemical cues associated with (i) mechanical damage, (ii) herbivore presence and (iii) grazing are the main factors triggering induced defences in both marine and freshwater phytoplankton, but most studies have failed to disentangle the exact mechanism(s) governing defence induction in any particular species. Induced defences in phytoplankton include changes in morphology (e.g. the formation of spines, colonies and thicker cell walls), biochemistry (such as production of toxins, repellents) and in life history characteristics (formation of cysts, reduced recruitment rate). Our categorization of inducible defences in terms of the responsible induction mechanism provides guidance for future work, as hardly any of the available studies on marine or freshwater plankton have performed all the treatments that are required to pinpoint the actual cue(s) for induction. We discuss the ecology of inducible defences in marine and freshwater phytoplankton with a special focus on the mechanisms of induction, the types of defences, their costs and benefits, and their consequences at the community level.