Affinity, capacity and oxygen sensitivity of two different mechanisms for bicarbonate utilization in Ulva lactuca L. (Chlorophyta)

Ulva lactuca, collected on the west coast of Sweden at the end of May, was able to utilize the HCO₃ ^? pool of seawater only through extracellular dehydration via carbonic anhydrase, followed by uptake of the CO₂ formed. A decrease in the CO₂ supply via this mechanism resulted in the gradual development of an additional method of HCO₃ ^? utilization, namely a direct uptake of HCO₃ ^? . Photosynthesis could then be supported by either a ‘HCO₃ ^? dehydration mechanism’ or a ‘HCO₃ ^? uptake mechanism’. Through selective inhibition of either of these mechanisms, the physiological properties of the other could be assessed. These properties suggest that the HCO₃ ^? uptake mechanism of U. lactuca is important under conditions when low concentrations of inorganic C, high pH and high external O₂ concentrations would limit photosynthesis supported by the HCO₃ ^? dehydration mechanism. Such conditions may occur during intense irradiation of the alga in rockpools or in shallow bays with low rates of water exchange. The results are discussed in relation to a possible coupling between mechanisms for inorganic C acquisition and cell structure (or even morphology) of green macroalgae. They also illustrate some necessary precautions when using Michaelis–Menten kinetics for estimations of V_max and K_1/2 values.     

在水生与气生状态下石莼光合作用对无机碳的响应

潮间带海藻光合作用总是处于水生 (高潮时 )与气生 (低潮时 )两种连续变化的环境状态下进行。对汕头沿岸常见的潮间带海藻石莼 (UlvalactucaL .)在水生和气生不同状态下光合作用对无机碳的响应特性进行了比较研究。在水生状态下 ,现有海水中溶解性无机碳浓度能充分饱和 (10℃和 2 0℃时 )或接近饱和 (30℃时 )石莼的光合作用 ;而在气生状态下 ,石莼光合作用受大气CO2 浓度的限制 ,且这种限制作用在较高温度 (2 0 - 30℃ )下比在低温(10℃ )下更严重。在 10℃和 2 0℃时 ,石莼在气生状态下比在水生状态下具有更高的碳饱和最大光合速率 ;而在30℃时 ,石莼在这两种状态下的碳饱和光合速率相似。石莼光合作用的Km(CO2 )值在气生状态下比在水生状态下高 ;而在气生状态下石莼对CO2 的表观光合导度远小于其在水生状态下的值。认为大气CO2 浓度升高将通过促进石莼在气生状态下的光合作用而增加其初级生产力。     

在水生与气生状态下石莼光合作用对无机碳的响应

潮间带海藻光合作用总是处于水生(高潮时)与气生(低潮时)两种连续变化的环境状态下进行.对汕头沿岸常见的潮间带海藻石莼(Ulva lactuca L.)在水生和气生不同状态下光合作用对无机碳的响应特性进行了比较研究.在水生状态下,现有海水中溶解性无机碳浓度能充分饱和(10 ℃和20 ℃时)或接近饱和(30 ℃时)石莼的光合作用;而在气生状态下,石莼光合作用受大气CO2浓度的限制,且这种限制作用在较高温度(20-30 ℃)下比在低温(10 ℃)下更严重.在10 ℃和20 ℃时,石莼在气生状态下比在水生状态下具有更高的碳饱和最大光合速率;而在30 ℃时,石莼在这两种状态下的碳饱和光合速率相似.石莼光合作用的Km (CO2)值在气生状态下比在水生状态下高;而在气生状态下石莼对CO2的表观光合导度远小于其在水生状态下的值.认为大气CO2浓度升高将通过促进石莼在气生状态下的光合作用而增加其初级生产力.     

Photosynthesis of Ulva fasciata. IV. pH, carbonic anhydrase and inorganic carbon conversions in the unstirred layer

Abstract. The common marine macroalga Ulva was found to have a surface pH of about 10 during photosynthesis. Under such a condition, the equilibrium CO₂ concentration within the unstirred layer would be below reported CO₂ compensation points, and dehydration of HCO₃ could not occur. Even at a compensation point approaching zero, uncatalysed rates of HCO₃ to CO₂ conversion within the unstirred layer volume could not support photosynthetic rates as measured under stirred conditions in the presence of a carbonic anhydrase inhibitor. Based on this, it is concluded that Ulva takes up HCO₃. It is likely that HCO₃ uptake leads to high internal CO₂ levels which, in turn, suppress photorespiration and thus cause this plant's efficient gas exchange features. Carbonic anhydrase activity was measurable only in plant extracts. However, inhibitor studies suggest the presence of a surface enzyme. The possible functions of extracellular carbonic anhydrase in Ulva are assessed in terms of CO₂ hydration during emergence and a possible HCO₃, transport system.     

Biosorption of mercury from aqueous solution by Ulva lactuca biomass

The mercury biosorption onto non-living protonated biomass of Ulva lactuca, as an alternative method for mercury removal from aqueous solutions, was investigated. Batch equilibrium tests showed that at pH 3.5, 5.5 and 7 the maxima of mercury uptake values, according to Langmuir adsorption isotherm, were 27.24, 84.74 and 149.25 mg/g, respectively. The ability of Ulva lactuca biomass to adsorb mercury in fixed-bed column, was investigated as well. The influence of column bed height, flow rate and effluent initial concentration of metal was studied. The adsorbed metal ions were easily desorbed from the algal biomass with 0.3 N H₂SO₄ solution. After acid desorption and regeneration with distilled water, the biomass could be reused for other biosorption assays with similar performances.     

Membrane potential measurements of marine macroalgae: Porphyra purpurea and Ulva lactuca

Abstract. Accumulation of the lipophilic cation tri-phenylmethylphosphonium (TPMP⁺) has been used to estimate the plasmalemma potential (Φm) of Porphyra purpurea (Rhodophyta, Bangiales) and Ulva lactuca (Chlorophyta, Ulvales). Values of Φm obtained using the Nernst equation were −61 mV and −54 mV respectively; these values compare well with those obtained using glass microelectrodes. A trend of hyperpolarization of Φm in P. purpurea was observed with decreasing external salinity. This hyperpolarization was shown to be primarily due to changes in external K⁺ concentration. Varying external Na⁺ concentration was found to have little effect on Φm. The present data suggest that the membrane potential of P. purpurea is not wholly due to a K⁺ diffusion potential, but may have an electrogenic component.     

The utilization of bicarbonate ions by the macroalga Ascophyllum nodosum (L.) Le Jolis

Abstract A comparison of some of the methods used to determine whether aquatic plants have the ability to utilize bicarbonate ions as a source of inorganic carbon for photosynthesis has been applied to the intertidal macroalga Ascophyllum nodosum. These include: observing photosynthesis at a high pH (below the alga's CO₂ compensation point), pH compensation point determinations, comparing the photosynthetic characteristics at low pH (5.20) and at high pH (7.95), estimating the maximal rates at which CO₂ can diffuse through the unstirred layer and the rate at which CO₂ can be produced from bicarbonate dehydration in the unstirred layer. All indicated that Ascophyllum nodosum can use bicarbonate ions for photosynthesis, though some were not always consistent. Calculating the total inorganic carbon concentration from pH measurements and acidification CO₂ determinations revealed that the assumption that the alkalinity remains constant during pH drift experiments is not always valid.     

The effect of temperature and oxygen on the CO2 compensation point of the marine alga Ulva lactuca

Abstract The CO₂ compensation point of Ulva lactuca frond sections has been measured in artificial seawater using a sensitive gas-chromatographic method. Under nitrogen the compensation point remained relatively constant at 3–6 cm³ m⁻³ at temperatures from 10 to 30°C while in air-saturated medium (0.3 kg m⁻³ O₂) the compensation point rose from 5 cm³ m⁻³ at 10°C to 11 cm³ m⁻³ at 30°C. These responses of the compensation point to temperature and oxygen concentration indicate that there is little photorespiratory CO₂ loss in this marine macroalga, and the low values of these compensation points indicate that inorganic carbon is actively accumulated by the plant.     

Production of recombinant protein in Escherichia coli cultured in extract from waste product alga,Ulva lactuca

This study examined the potential for waste product alga, Ulva lactuca, to serve as a media component for recombinant protein production in Escherichia coli. To facilitate this investigation, U. lactuca harvested from Jamaica Bay was dried, and nutrients acid extracted for use as a growth media. The E. coli cell line BL21(DE3) was used to assess the effects on growth and production of recombinant green fluorescent protein (GFP). This study showed that media composed of acid extracts without further nutrient addition maintained E. coli growth and recombinant protein production. Extracts made from dried algae lots less than six‐months‐old were able to produce two‐fold more GFP protein than traditional Lysogeny Broth media. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:784–789, 2014     

光照和温度对氮饥饿及饱和营养条件下石莼(Ulva lactuca)的硝态氮吸收动力学影响

为探讨海藻养分吸收能力并以高效养分过滤器筛选为目标,以N饥饿和N饱和的石莼为材料,研究了3种光照及温度因子及其交互作用对不同N素营养限制状态下石莼NO3-吸收动力学特征的影响。结果表明:N饱和条件下,随着光照的增强,石莼对NO3-的最大吸收速率也增加;30℃条件下,光照强度的增加虽然使得其最大吸收速率提高,但Vmax/Km在中等光强下最大;20℃最有利于石莼对NO3-的吸收。N饥饿条件下,石莼对NO3-的吸收速率显著大于非饥饿状态。在10℃和20℃条件下,呈现与N饱和条件下相似的规律,但在30℃条件下,中等光强石莼对NO3-的最大吸收速率最高。在10℃和20℃条件下,增加光强促进石莼对NO3-的吸收,但30℃条件下光强的增加并未起到促进作用。饥饿状态下的石莼的NO3-吸收速率较高,当石莼吸收NO3-饱和时,依然可以以较低的速率继续吸收环境中的NO3-。     

A screening procedure for the solubilization of chloroplast membrane proteins from the marine green macroalga Ulva lactuca using RP-HPLC-MALDI-MS

A protocol for purification and analysis of chloroplast membrane proteins in the green macroalga Ulva lactuca has been developed, including reversed phase high performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Five different solvents were evaluated for extraction of membrane proteins by three methods. The highest protein yield was achieved when proteins were extracted directly from the chloroplasts using the solvent hexafluoroisopropanol. A range of proteins of increasing hydrophobicity was separated by HPLC. Analysis of both HPLC fractions and non-separated samples by MALDI-TOF-MS revealed proteins with molecular weights spanning between 1 and 376 kDa.     

The active uptake of carbon dioxide by the marine diatoms Phaeodactylum ticornutum and Cyclotella sp.

Mass spectromelry has been used to investigate the uptake of CO₂ by two marine diatoms, Phaeodactylum tricornutum and Cyclotella sp. The time course of CO₂ formation in the dark after addition of 100 mmol m^?3 dissolved inorganic carbon (DIC) to cell suspensions showed that external carbonic anhydrase (CA) was not present in cells of P. tricornutum but was present in Cyclotella sp. In the absence of external CA, or when it was inhibited by 5 mmol m^?3 acetazolamide, cells of both species preincubated with 100 mmol m^?3 DIG rapidly depleted almost all of the free CO₂ (3·2mmol m^?31 at pH7·5) from the suspending medium within seconds of illumination and prior to the onset of steady-state photosynthesis. Addition of bovine CA quickly restored the HCO₃^?–CO₂ equilibrium in the medium, indicating that the initial depletion of CO₂ resulted from the selective uptake of CO₂ rather than uptake of all DIG species. Transfer of cells to the dark caused a rapid increase in the CO₂ concentration in the medium, largely as a result of the efflux of unfixed inorganic carbon from the cells. The measured CO₂ uptake rates for both species accounted for 50% of the total DIG uptake at HCO₃^?–CO₂ equilibrium, indicating that HCOHCO₃^? was also being taken up. These results indicate that both Phaeodactylum tricornutum and Cyclotella sp. have the capacity to transport CO₂ actively against concentration and pH gradients.     

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)

Direct comparisons between photosynthetic O₂ evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400–600 μmol photons m⁻² s⁻¹. O₂ exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((F_m′−F_t)/F_m′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0–300 μmol photons m⁻² s⁻¹), there was a significant correlation between O₂ evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O₂ evolution tended towards an asymptote. However at high irradiance levels (600–1200 μmol photons m⁻² s⁻¹) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO₃ ⁻], [NH₄ ⁺] and [HPO₄ ^2-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O₂ evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O₂, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances. This revised version was published online in June 2006 with corrections to the Cover Date.