中国近海浮游植物生产的二甲基硫和二甲基硫丙酸的分布状况及其影响因素

于1994～1998年期间调查了浮游植物生产的生源气候气体二甲基硫(DMS)及其前身二甲基硫丙酸(DMSPp)在我国胶州湾、芝罘湾、东海的分布状况及其影响因素.结果表明,自然海区中二者浓度都存在明显的时空变化.地理分布规律是,高值出现在沿岸海区和陆架海区,低值出现在外海特别是贫营养海区.就不同季节而言,高值出现在春季或夏季,低值出现在秋季.DMS或DMSPp的分布在大尺度上主要受海流和水团的影响,而在小尺度上营养条件和生物因子则更重要.在近岸海区,硅藻是DMS和DMSPp的重要贡献者.研究海区硝酸盐与DMSPp的关系有两种情况:当硝酸盐浓度低于1μmol/L时,二者为正相关,硝酸盐浓度高于这个阈值时,二者为负相关.表明浮游植物细胞中二甲基硫丙酸作为渗透压调节物质其含量受到氮源可得性的调控.此外,研究结果还显示,生活污水入海、海水养殖等也对DMS和DMSPp的浓度分布有一定影响.     

中国近海浮游植物生产的二甲基硫和二甲基硫丙酸的分布状况及其影响因素

于1994-1998年期间调查了浮游植物生产的生源气候气体二甲基硫(DMS)及其前身二甲基硫丙酸(DMSPp)在我国胶州湾、芝罘湾、东海的分布状况及其影响因素。结果表明,自然海区中二者浓度都存在明显的时空变化。地理分布规律是,高值出现在沿岸海区和陆架海区,低值出现在外海特别是贫营养海区。就不同季节而言,高值出现在春季或夏季,低值出现在秋季。DMS或DMSPp的分布在大尺度上主要受海流和水团的影响,而在小尺度上营养条件和生物因子则更重要。在近岸海区,硅藻是DMS和 DMSPp的重要贡献者。研究海区硝酸盐与DMSPp的关系有两种情况：当硝酸盐浓度低于1 μmol／L时,二者为正相关,硝酸盐浓度高于这个阈值时,二者为负相关。表明浮游植物细胞中二甲基硫丙酸作为渗透压调节物质其含量受到氮源可得性的调控。此外,研究结果还显示,生活污水入海、海水养殖等也对DMS和DMSPp的浓度分布有一定影响。     

ISOLATION, PURIFICATION, AND CHARACTERIZATION OF DMSP LYASE (DIMETHYLPROPIOTHETIN DETHIOMETHYLASE (4.4.1.3)) FROM THE RED ALGA POLYSIPHONIA PANICULATA1

Polysiphonia paniculata Montagne is an intertidal red alga known to produce large amounts of the compound dimethylsulfoniopropionate (DMSP). Conversion of this substrate into dimethylsulfide is accomplished in P, paniculata by an enzyme called DMSP lyase (dimethylpropiothetin dethiomethyla.se (4.4.1.3)). DMSP lyase has been purified and characterized from P. paniculata. Enzymie activity is found in two different proteins: the larger with a molecular weight of 9.26 ± 10⁴ daltons and the smaller with a molecular weight of 3.65 ± 10⁴ daltons. Specific activity of the enzyme is 526 μmols min⁻¹mg⁻¹ for the smaller protein a nd 263 μmols min ⁻¹ mg⁻¹ for the la rger protein. The Michaelis-Menten constant (K_m) is 72.8 μM ± 17.15 and the v_max is 1.62 μmols min⁻¹± 0.928 for the 92.6-kDa protein. The p1 of the larger protein is 5.8 and 5.9 for the smaller protein. Interaction with cysteine protease inhibitors L-trans-epoxysuccinyl-leucylamido (4-guanidino)-butane, dithiobis-(2-nitrobenzoate), or N -ethylmaleimide inactivated enzyme activity. The presence of either magnesium or calcium with DMSP lyase enhanced activity al concentrations between 20 and 40 μM but had little effect above these levels. Addition of the divalent chelators ethylenebis(oxyethylenenitrilo) tetraacetic acid and ethylenediaminetetraacetate decreased activity of the enzyme, but activity was restored when either chelator was removed and magnesium or calcium was added to the enzyme .     

SEASONAL PATTERN OF DIEL PERIODICITY IN PHOTOSYNTHESIS BY POLAR PHYTOPLANKTON: SPECIES-SPECIFIC RESPONSES1

The diel patterns of light-saturated and light-limited photosynthesis were measured for three diatom species in McMurdo Sound, Antarctica during the transition from late austral winter to summer. Maximum photosynthetic capacity occurred around mid-day during September, when there was a well defined light/dark cycle, and progressively shifted to about midnight by late october when irradiance was continuous. There was a concomitant shift in minimum photosynthetic capacity from midnight to midday. Rates of light-saturated and -limited photosynthesis covaried, and the magnitude of seasonal and diel changes in photosynthetic characteristics were similar. The linear relationship between light-saturated and -limited photosynthesis suggests that the shapes of the photosynthesis-irradiance curves remained relatively constant over the day and througout the season. The unique diel patterns of photosynthesis of these polar phytoplankton appear to be a response to the persistently low, yet continuous irradiance of the polar summer.     

Light absorption and scattering by cell suspensions of some cyanobacteria and microalgae

Absorption spectra of cyanobacteria (Anacystis nidulans, Anabaena variabilis, and Chlorogloeopsis fritschii), red (Cyanidium caldarum and Porphyridium cruentum), green (Dunaliella maritima and Dunaliella salina) and diatom (Thalassiosira weisflogii) alga cell suspensions are presented; the spectra were obtained by using an approach developed earlier to compensate for scattering [1, 2]. In all species, the shapes of the absorption spectra were independent of the cell concentration. For Th. weisflogii and D. maritima, the analysis of selective and nonselective scattering was carried out. The effect of mechanical cell disruption on optical properties (absorption, scattering, and “package” effect) on D. maritima was studied. The character and dynamics of optical changes in D. salina under the influence of sodium chloride were followed.     

Monitoring river periphyton with artificial benthic substrates

The objective of this research was to identify the materials and methods necessary to study the attached algal community on a river bottom in deep water. The study site was the Susquehanna River near Falls, Pennsylvania. Artificial substrates of smooth glass, frosted glass, Vermont slate, sandy slate (flagstone) and acrylic plate were placed on the stream bottom in detritus free sample holders by scuba divers. Both monthly and long-term cumulative samples were collected from the plates employing scuba and a Bar-Clamp sampler. River stones (natural substrates) were collected for comparison. Samples were analyzed in a Palmer Cell under a Bausch and Lomb research microscope. Diatoms were the most important colonizers of river stones, with the genera Nitzschia and Navicula most abundant. Highest periphyton densities occurred on natural substrates in winter with a maximum of 2.2 × 10⁴ units/ mm². Artificial substrates with one month exposure periods accumulated maximum periphyton density from May through October with relatively low densities in winter. Cumulative artificial substrates were most like river stones in patterns of colonization. Frosted acrylic is recommended for future studies employing benthic artificial periphyton substrates.This study was partially supported by the Pennsylvania Power and Light Company     

RUBISCO ADAPTATION TO LOW TEMPERATURES: A COMPARATIVE STUDY IN PSYCHROPHILIC AND MESOPHILIC UNICELLULAR ALGAE

Some properties of the ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) from two psychrophilic Chloromonas species have been investigated in relation to their adaptation to cold environments. Contrary to the situation usually encountered with psychrophilic enzymes, the carboxylase activity of both purified "cold" RUBISCO enzymes was lower at low temperatures than that found with the enzyme of the mesophilic alga Chlamydomonas reinhardtii Dangeard. Moreover, the apparent optimal temperature for RUBISCO carboxylase activity was similar for psychrophilic and mesophilic enzymes. Psychrophilic RUBISCOs, however, showed a greater thermosensitivity than the C. reinhardtii enzyme. Genes encoding small and large subunits of RUBISCO from one psychrophilic isolate were sequenced. Comparison of the deduced amino acid sequences to those of higher plants and green algae revealed the substitution of a very highly conserved residue (cysteine₂₄₇ → serine in the large subunit) that could be responsible, at least in part, for the increased thermosensitivity of the "cold" enzyme. Interestingly, the relative amount of RUBISCO subunits found in the psychrophilic isolates was about twice as high as the amount observed in C. reinhardtii and five other mesophilic algae. The high production of a key enzyme to counterbalance its poor catalytic efficiency at low temperature could constitute a novel type of adaptive mechanism to cold environments.