GROWTH,PHOTOSYNTHESIS AND MAINTENANCE METABOLIC COST IN THE DIATOM PHAEODACTYLUM TRICORNUTUM AT VERY LOW LIGHT LEVELS 1

The compensation point for growth of Phaeodactylum tricornutum Bohlin is less than 1 μmol. m^?2s^?1. Growth at low PFDs (<3.5 μmol. m^?2.s^?1) does not appear to reduce the maximum quantum efficiency of photosynthesis (ø_m) or to greatly inhibit the potential for light-saturated, carbon-specific photosynthesis (P_m^c). The value for ø_m in P. tricornutum is 0.10–0.12 mol O₂-mol photon^?1, independent of acclimation PFD between 0.75 and 200 μmol.m^?2.s^?1 in nutrient-sufficient cultures. P_m^c in cells of P. tricornutum acclimated to PFDs <3.5 μmol m^?2?s^?1 is approximately 50% of the highest value obtained in nutrient-sufficient cultures acclimated to growth-rate-saturating PFDs. In addition, growth at low PFDs does not severely restrict the ability of cells to respond to an increase in light level. Cultures acclimated to growth at lees than 1% of the light-saturated growth rate respond rapidly to a shift-up in PFD after a short initial lag period and achieve exponential growth rates of 1.0 d^?1 (65% of the light- and nutrient-saturated maximum growth rate) at both 40 and 200 μmol.m^?2.s^?1     

PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P. “pseudolinearis” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance (P–I) curves revealed that maximal photosynthesis (P_max), irradiance at maximal photosynthesis (I_max), and compensation irradiance (I_c) varied with salinity, temperature, and species. The P_max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O₂ · g dwt^?1 · h^?1 (where dwt indicates dry weight) at 30–140 μmol photons · m^?2 · s^?1 (I_max) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m^?2·s^?1, and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P_max values but higher I_max values than those of P. abbottiae. The P_max of P. “pseudolinearis” conchocelis was 200–240 μmol O₂ · g dwt^?1 · h^?1 and for P. torta was 90–240 μmol O₂ · g dwt^?1 · h^?1. Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m^?2 · s^?1 at 30 psu, but P_max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m^?2 · s^?1, and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances (I_c) were relatively low (3–5 μmol · photons · m^?2 · s^?1) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.     

LIGHT DEPENDENCE OF GROWTH AND PHOTOSYNTHESIS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Phaeodactylum tricornutum Bohlin was maintained in exponential growth over a range of photon flux densities (PFD) from 7 to 230 μmol·m^?2s^?1. The chlorophyll a-specific light absorption coefficient, maximum quantum yield of photosynthesis, and C:N atom ratio were all independent of the PFD to which cells were acclimated. Carbon- and cell-specific, light-satuated, gross photosynthesis rates and dark respiration rates were largely independent of acclimation PFD. Decreases in the chlorophyll a-specific, gross photosynthesis rate and the carbon: chlorophyll ratio and increases of cell- or carbon-specific absorption coefficients were associated with an increase in cell chlorophyll a in cultures acclimated to low PFDs. The compensation PFD for growth was calculated to be 0.5 μmol·m^?2s^?1. The maintenance metabolic rate (2 × 10^?7s^?1), calculated on the basis of the compensation PFD, is an order of magnitude lower than the measured dark respiration rate(2.7 × 10^?6mol O₂·mol C^?1s^?1). Maintenance of high carbon-specific, light-saturated photosynthesis rates in cells acclimated to low PFDs may allow effective use of short exposures to high PFDs in a temporally variable light environment.     

PHOTOSYNTHESIS,DARK RESPIRATION AND DESICCATION RESISTANCE OF THE INTERTIDAL SEAWEEDS HESPEROPHYCUS HARVEYANUS AND PELVETIA FASTIGIATA F. GRACILIS12

Rates of net photosynthesis and dark respiration were determined under submersed and emerged conditions for Hesperophycus harveyanus S. & G. and Pelvetia fastigiata f. gracilis (Decne.) S. & G. Both species exhibited submersed photosynthesis-light relationships and dark respiration rates similar to those established for other closely related intertidal, fucoids. Maximal net photosynthesis of H. harveyanus (0.21 mmol O₂ g dry wt.^-1· h^-1; 0.18 mmol CO₂ g dry wt.^-1· h^-1) was similar to that of P. fastigiata f. gracilis (0.17 mmol. O₂ g dry wt.^-1· h^-1; 0.14 mmol CO₂ g dry wt. ^-1· h^-1). Light saturation occurred between 150 and 250 μE · m^-2· s^-1 for H. harveyanus and between 75 and 150 μE · m^-2· s^-1 for P. fastigiata f. gracilis; photon flux densities required for compensation were 6.4 and 9.2 μE · m^-2· s^-1, respectively. Photoinhibition was not observed for either species. The light-saturated, submersed net photosynthetic performances of both species varied significantly with temperature. Greatest photosynthetic rates were obtained at 23° C for H. harveyanus and at 18° C for P. fastigiata f. gracilis. Under emersed conditions, the maximal net photosynthetic rate and the photon flux densities required for saturation were greater for H. harveyanus (0.08 mmol CO₂ g dry wt.^-1· h^-1; 260 to 700 μE · m^-2· s^-1) than for P. fastigiata f. gracilis (0.02 mmol CO₂g dry wt.^-1· h^-1; 72 to 125 μE · m^-2· s^-1). However, for both species, emersed photosynthetic rates were much lower (14–44%) than those obtained under submersed conditions. Desiccation negatively influenced emersed photosynthesis, of both species, but H. harveyanus thalli contained more water when fully hydrated and lost water more slowly during dehydration, thus suggesting greater photosynthetic potential during field conditions of emersion.     

Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina

Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m^?2 s^?1. When measured at a standard temperature (17°C), rates of light-saturated photosynthesis (P_max) were higher in 5 °C-grown algae (c. 3.0 μmol O₂ m^?2 s^?1) than in 17 °C-grown algae (c. 0.9 μmol O₂ m_-2 s_-1). Concentrations of Rubisco were also 3-fold higher (per unit protein) in 5 °C-grown algae than in algae grown at 17 °C. Light-limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low-light algae absorbed c. 75% of incident light, whereas 5 °C high-light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin-Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0_max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low-light-grown algae was twice that of high-light-grown algae (c. 160.0 versus 80.0 nmol m^?2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.     

Influence of light and temperature on photosynthesis and respiration by Pithophora oedogonia (Mont.) Wittr. (chlorophyceae)

Rates of net photosynthesis and respiration were determined for Pithophora oedogonia (Mont.) Wittr. acclimatized to 56 combinations of light (7–1200 μE m^?2 s^?1) and temperature (5–35°C). Conditions for maximum net photosynthesis were estimated to be 26°C and 970 μE m^?2 s^?1. The rate of net photosyntheses varied considerably with temperature, with the maximum measured value (9.67 mg O₂ h^?1 g dry wt.^?1) occurring at 25°C. Respiration rate increased with temperature and the light received just prior to measurement. The maximum respiration rate (7.05 mg O₂ g^?1 h^?1) occurred at 30°C and 1200 μE m^?2 s^?1. Exposure of Pithophora to light levels of 600 or 1200 μE m^?2 s^?1 prior to determination of the respiration rate resulted in significantly elevated levels of oxygen consumption at temperatures ≥ 15°C. The relationship between light, temperature and photosynthesis and respiration were summarized as three-dimensional response surfaces.     

Photosynthetic performance of freshwater Rhodophyta in response to temperature, irradiance, pH and diurnal rhythm

Responses of net photosynthetic rates to temperature, irradiance, pH/inorganic carbon and diurnal rhythm were analyzed in 15 populations of eight freshwater red algal species in culture and natural conditions. Photosynthetic rates were determined by oxygen concentration using the light and dark bottles technique. Parameters derived from the photosynthesis–irradiance curves indicated adaptation to low irradiance for all freshwater red algae tested, confirming that they tend to occur under low light regimes. Some degree of photo‐inhibition (β= ‐0.33–0.01 mg O₂ g^?1 DW h^?1 (μmol photons m^?2 s^?1)^?1) was found for all species/populations analyzed, whereas light compensation points (Ic) were very low (≤ 2 μmol photons m‐ photons s^?1) for most algae tested. Saturation points were low for all algae tested (Ik = 6–54 μmol photons m^?2 s^?1; Is = 20–170 umol photons m^?2 s^?1). Rates of net photosynthesis and dark respiration responded to the variation in temperature. Optimum temperature values for net photosynthesis were variable among species and populations so that best performances were observed under distinct temperature conditions (10, 15, 20 or 25°C). Rates of dark respiration exhibited an increasing trend with temperature, with highest values under 20–25°C. Results from pH experiments showed best photosynthetic performances under pH 8.5 or 6.5 for all but one species, indicating higher affinity for inorganic carbon as bicarbonate or indistinct use of bicarbonate and free carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for all algae tested, which was characterized by two relatively clear peaks, with some variations around it: a first (higher) during the morning (07.00–11.00 hours.) and a second (lower) in the afternoon (14.00–18.00 hours). Comparative data between the ‘Chantransia’ stage and the respective gametophyte for one Batrachospermum population revealed higher values (ca 2‐times) in the latter, much lower than previously reported. The physiological role of the ‘Chantransia’ stage needs to be better analyzed.     

Seasonal Growth and Photosynthetic Performance of the Antarctic Macroalga Desmarestia menziesii (Phaeophyceae) Cultivated under Fluctuating Antarctic Daylengths

Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d^?1 in winter condition (July-August) to 0.5% d^?1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g^?1 FW (chlorophyll a), 0.4 mg g^?1 FW (chlorophyll c) and 0.9 mg g^?1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (P_max), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O₂ g^?1 FW h^?1 in October and minima close to 9μmol O₂ g^?1 FW h^?1 in April. Dark respiration was high in spring (13μmol O₂ g^?1 FW h^?1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (l_k) increased significantly in spring [1.3 μimol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 and 26μmol photons m^?2 s^?1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

Effects of salinity,light intensity and sediment on growth,pigments, agar production and reproduction in Gracilaria tenuistipitata from Songkhla Lagoon in Thailand

The effects of salinity, light intensity and sediment on Gracilaria tenuistipitata C.F. Chang & B.M. Xia on growth, pigments, agar production, and net photosynthesis rate were examined in the laboratory under varying conditions of salinity (0, 25 and 33 psu), light intensity (150, 400, 700 and 1000 µmol photons m^?2 s^?1) and sediment (0, 0.67 and 2.28 mg L^?1). These conditions simulated field conditions, to gain some understanding of the best conditions for cultivation of G. tenuistipitata. The highest growth rate was at 25 psu, 700 µmol photons m^?2 s^?1 with no sediments, that provided a 6.7% increase in weight gain. The highest agar production (24.8 ± 3.0 %DW) was at 25 psu, 150–400 µmol photons m^?2 s^?1 and no sediment. The highest pigment contents were phycoerythrin (0.8 ± 0.5 mg g^?1FW) and phycocyanin (0.34 ± 0.05 mg g^?1 FW) produced in low light conditions, at 150 µmol photons m^?2 s^?1. The highest photosynthesis rate was 161.3 ± 32.7 mg O₂ g^?1 DW h^?1 in 25 psu, 400 µmol photons m^?2 s^?1 without sediment in the short period of cultivation, (3 days) and 60.3 ± 6.7 mg O₂ g^?1 DW h^?1 in 25 psu, 700 µmol photons m^?2 s^?1 without sediment in the long period of cultivation (20 days). The results indicated that salinity was the most crucial factor affecting G. tenuistipitata growth and production. This would help to promote the cultivation of Gracilaria cultivation back into the lagoon using these now determined baseline conditions. Extrapolation of the results from the laboratory study to field conditions indicated that it was possible to obtain two crops of Gracilaria a year in the lagoon, with good yields of agar, from mid‐January to the end of April (dry season), and from mid‐July to the end of September (first rainy season) when provided sediment was restricted.     

CO2 exchange in the alpine sedge Carex curvula as influenced by canopy structure,light and temperature

Summary The temperature and light responses of CO₂ uptake (F_n) in the sedge Carex curvula were investigated in situ by IRGA technic in the Austrian Central Alps at an altitude of 2,310 m. F_n in Carex leaves reaches a maximum of 15.6 mg CO₂ dm^-2 h^-1 at a leaf temperature of 22.5°C and a quantum flux density larger than 1.0 mmol photons m^-2 s^-1 (400–700 nm). A model based on a polynomal regression analysis of the F_n responses and informations about the microclimate and the canopy structure was used to simulate F _n for individual days and for a whole season. It turned out that the major rate limiting factor is the availability of light in the canopy: The calculated photosynthetic yield for a hypothetical optimum season of clear days with fully illuminated leaves and optimum temperature as well as for a typical season with the actual light and temperature conditions in the canopy, shows that insufficient illumination of the leaves accounts for almost 40% reduction of the possible CO₂ uptake while suboptimal temperatures cause only a loss of 8%. Half of the light deficit is caused by mutual shading of the leaves. The minor importance of temperature for the annual CO₂ uptake results from the fact that temperature adaptation of F _n in this sedge allows optimal utilization of short periods with high light intensity and hence high photosynthetic yield. The weaker the quantum supply the more becomes temperature limiting. This indicates that the length of the growing season is probably less important for the success of this prominent alpine plant than the sum of hours with high radiation.List of Symbols I _o quantum flux density in a horizontal plane above the plant canopy (mol photons m^-2 s^-1, 400–700 nm) - I _z as I _o, but at level z in the leaf canopy - I ₁ quantum flux density received by a leaf at level z and with leaf inclination (for diffuse light I _z=I ₁) - solar elevation angle (°) - leaf angle to the vertical (°) - extinction coefficient - LAI leaf area index - T ₁ leaf temperature (°C) - F _n rate of net photosynthesis (CO₂ uptake; mg CO₂ g dry weight^-1 h^-1, or mg CO₂ dm^-2 h^-1, projected leaf area) - R _d rate of dark respiration (mg CO₂ g^-1 h^-1)     

LIGHT AND TEMPERATURE AS FACTORS REGULATING SEASONAL GROWTH AND DISTRIBUTION OF ULOTHRIX ZONATA (ULVOPHYCEAE)1

Ulothrix zonata (Weber and Mohr) Kütz. is an unbranched filamentous green alga found in rocky littoral areas of many northern lakes. Field observations of its seasonal and spatial distribution indicated that it should have a low temperature and a high irradiance optimum for net photosynthesis, and at temperatures above 10°C it should show an increasingly unfavorable energy balance. Measurements of net photosynthesis and respiration were made at 56 combinations of light and temperature. Optimum conditions were 5°C and 1100 μE·m^?2·s^?1 at which net photosynthesis was 16.8 mg O₂·g^?1·h^?1. As temperature increased above 5° C optimum irradiance decreased to 125 μE·m^?2·s^?1 at 30°C. Respiration rates increased with both temperature and prior irradiance. Light-enhanced respiration rates were significantly greater than dark respiration rates following irradiance exposures of 125 μE·m^?2·s^?1 or greater. Polynomials were fitted to the data to generate response surfaces. Polynomial equations represent statistical models which can accurately predict photosynthesis and respiration for inclusion in ecosystem models.     

Response of the Ubiquitous Pelagic Diatom Thalassiosira weissflogii to Darkness and Anoxia

Thalassiosira weissflogii, an abundant, nitrate-storing, bloom-forming diatom in the world’s oceans, can use its intracellular nitrate pool for dissimilatory nitrate reduction to ammonium (DNRA) after sudden shifts to darkness and anoxia, most likely as a survival mechanism. T. weissflogii cells that stored 4 mM ¹⁵N-nitrate consumed 1.15 (±0.25) fmol NO₃ ^- cell^-1 h^-1 and simultaneously produced 1.57 (±0.21) fmol ¹⁵NH₄ ⁺ cell^-1 h^-1 during the first 2 hours of dark/anoxic conditions. Ammonium produced from intracellular nitrate was excreted by the cells, indicating a dissimilatory rather than assimilatory pathway. Nitrite and the greenhouse gas nitrous oxide were produced at rates 2-3 orders of magnitude lower than the ammonium production rate. While DNRA activity was restricted to the first few hours of darkness and anoxia, the subsequent degradation of photopigments took weeks to months, supporting the earlier finding that diatoms resume photosynthesis even after extended exposure to darkness and anoxia. Considering the high global abundance of T. weissflogii, its production of ammonium and nitrous oxide might be of ecological importance for oceanic oxygen minimum zones and the atmosphere, respectively.     

Dunaliella salina (Chlorophyta) with small chlorophyll antenna sizes exhibit higher photosynthetic productivities and photon use efficiencies than normally pigmented cells

The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to different light intensities were investigated. Batch cultures were grown to the mid-exponential phase under continuous low-light (LL: 100 μmol photon m^-2 s^-1) or high-light (HL: 2000 μmol photon m^-2 s^-1) conditions. Under LL, cells were normally pigmented (deep green) containing ∼500 chlorophyll (Chl) molecules per photosystem II (PSII) unit and ∼250 Chl molecules per photosystem I (PSI). HL-grown cells were yellow-green, contained only 60 Chl per PSII and 100 Chl per PSI and showed signs of chronic photoinhibition, i.e., accumulation of photodamaged PSII reaction centers in the chloroplast thylakoids. In LL-grown cells, photosynthesis saturated at ∼200 μmol photon m^-2 s^-1 with a rate (P_max) of ∼100 mmol O₂ (mol Chl)^-1 s^-1. In HL-grown cells, photosynthesis saturated at much higher light intensities, i.e. ∼2500 μmol photon m^-2 s^-1, and exhibited a three-fold higher P_max (∼300 mmol O₂ (mol Chl)^-1 s^-1) than the normally pigmented LL-grown cells. Recovery of the HL-grown cells from photoinhibition, occurring prior to a light-harvesting Chl antenna size increase, enhanced P_max to ∼675 mmol O₂ (mol Chl)^-1 s^-1. Extrapolation of these results to outdoor mass culture conditions suggested that algal strains with small Chl antenna size could exhibit 2–3 times higher productivities than currently achieved with normally pigmented cells. This revised version was published online in August 2006 with corrections to the Cover Date.     

CYTOCHROME f LOSS IN ASTAXANTHIN-ACCUMULATING RED CELLS OF HAEMATOCOCCUS PLUVIALIS (CHLOROPHYCEAE): COMPARISON OF PHOTOSYNTHETIC ACTIVITY, PHOTOSYNTHETIC ENZYMES, AND THYLAKOID MEMBRANE POLYPEPTIDES IN RED AND GREEN CELLS

Photosynthetic activity, chloroplast enzymes, and poly-peptides were compared in green and red (ketocarotenoid-containing) cultures of the microalga Haematococcus pluvialis Flotow. Green cultures, grown at 80 μmol pho-tons.m^-2. s^-1 in an acetate-containing medium, had a mean generation time of 27 h. Ketocarotenoid accumulation was induced by transfer of green cultures to PO₄-deficient medium and exposure to 250 μmol photons.m^-2. s^-1. Under these conditions, there was no increase in cell number, and the cultures turned red. Relative amounts of enzymes and thylakoid polypeptides in red and green cells were ascertained by immunoprobing with standardization on a chlorophyll (Chl) basis. In red cultures, the level of cytochrome f was greatly decreased (< 1% of green cell level), which is expected to greatly impair the linear electron flow from photosystem (PS) II to PS I. Also, the levels of apoproteins in red cells, namely, of CPI, D2, CP47, LHC I, and ribulose-1, 5-bisphosphate carboxylase were reduced to 15, 18, 29, 48, and 80%, respectively, of those in green cells. Only adenosine triphosphate syn-thase exhibited no significant change in the two types of cultures. The respiration rate of red cultures was much higher (100 μmoles O₂. mg Chl^-1.h^-1) than that of green cells (16 μmoles O₂. mg Chl^-1.h^-1). Conversely, net O₂ evolution (at P_max in green cultures was 80 μmoles O₂. mg Chl^-1.h^-1 but was —40 μmoles O₂. mg Chl^-1.h^-1 in red cultures. PS II activity was demonstrated in broken cells of both green and red cultures, showing activity of 40 and 15 μmoles DCPIP-mg Chl^-1.h^-1 (with DPC as electron donor), respectively. In contrast, PS I activity measured by the Mehler reaction showed that red rather than green cells had a greater activity (64 vs. 46 μmoles O₂. mg Chl^-1.h^-1, respectively). Thus, in spite of the decline of O₂ evolution in red cells, the photosystems were still functional. We postulate that the decline of O₂, evolution in red cells is largely attributable to an increase in the respiration rate and the impairment of linear electron flow from PS II to PS I and, to some extent, to a decrease in components of the photosystems.     

PHOTOADAPTATION,GROWTH AND PRODUCTION OF BOTTOM ICE ALGAE IN THE ANTARCTIC1

Biomass, chemical composition, growth rates and the photosynthetic response of natural populations of sea ice algae in McMurdo Sound, Antarctica were followed over most of the spring bloom to examine temporal variability under a relatively constant incident irradiance (ca. 1500–1700 μE · m^-2· s^-1 at solar noon). Collection were restricted to bottom 20 cm of the ice sheet in an area with little or no snow (0–5 cm). At low temperature and irradiance these algae normally exhibited low assimilation numbers (ca. 0.1–0.4 mg C · mg Chl^-1· h^-1). Average growth rates (0.02–0.45 d^-1), based on changes in standing stocks, were also low. Biomass, biochemical composition, growth rates, assimilation numbers and photosynthetic efficiencies (mg C · mg Chl^-1· h^-1 (μE · m^-2· s^-1)^-1) displayed large fluctuations over periods of several days during the growth season. On the other hand, I_k which is an index of photoadaptation, and I_m, the optimal irradiance for photosynthesis, were relatively constant with less than twofold variation throughout our study. Substantial nutrient fluxes (3.3–8.0 mmol Si or N · m^-2· d^-1) were necessary to satisfy the minimum nutrient demand for the observed biomass levels and population growth rates; over the 41 days of our study, integrated nutrient demand represented 69–150 mmol N or Si · m^-2, Only 5–25% of this total demand could be met by all of the nutrients in the ice sheet, if they were readily available. However, adequate amounts were present in the top few meters of the water column. With small nutrient gradients in surface waters below the sea ice, vertical eddy diffusivities on the order of 3.8–9.3 cm²· s^- should supply sufficient nutrients to meet algal demand.     

AUTOTROPHIC GROWTH AND PHOTOACCLIMATION IN KARLODINIUM MICRUM (DINOPHYCEAE) AND STOREATULA MAJOR (CRYPTOPHYCEAE)1

We compared autotrophic growth of the dinoflagellate Karlodinium micrum (Leadbeater et Dodge) and the cryptophyte Storeatula major (Butcher ex Hill) at a range of growth irradiances (E_g). Our goal was to determine the physiological bases for differences in growth–irradiance relationships between these species. Maximum autotrophic growth rates of K. micrum and S. major were 0.5 and 1.5 div.·d^?1, respectively. Growth rates were positively correlated with C‐specific photosynthetic performance (PP^C, g C·g C^?1·h^?1) (r²=0.72). Cultures were grouped as light‐limited (LL) and high‐light (HL) treatments to allow interspecific comparisons of physiological properties that underlie the growth–irradiance relationships. Interspecific differences in the C‐specific light absorption rate (E_a^C, mol photons·g C^?1·h^?1) were observed only among HL acclimated cultures, and the realized quantum yield of C fixation (φ_C(real.), mol C·mol photons^?1) did not differ significantly between species in either LL or HL treatments. The proportion of fixed C that was incorporated into new biomass was lower in K. micrum than S. major at each E_g, reflecting lower growth efficiency in K. micrum. Photoacclimation to HL in K. micrum involved a significant loss of cellular photosynthetic capacity (P_max^cell), whereas in S. major, P_max^cell was significantly higher in HL acclimated cells. We conclude that growth rate differences between K. micrum and S. major under LL conditions relate primarily to cell metabolism processes (i.e. growth efficiency) and that reduced chloroplast function, reflected in PP^C and photosynthesis–irradiance curve acclimation in K. micrum, is also important under HL conditions.     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.     

PRODUCTIVITY OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYTA) IN SURREY LAKE,INDIANA1

Biomass, akinete numbers, net photosynthesis, and respiration of Pithophora oedogonia were monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO₂·g^?1 dry wt·h^?1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m^?2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO₃-N and PO₄-P in 1981. Laboratory investigations of temperature and light effects on Pithophora photosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest P_max value occurred at 35°C (0.602 μmol O₂·mg^?1 chl a·min^?1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of I_k(47 μE·m^?2·s^?1) and I_c (6 μE·m^?2·s^?1). Comparison of P. oedogonia and Cladophora glomerata indicated that the former was more tolerant of temperatures above 30°C. Pithophora's tolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littoral areas inhabited by this filamentous alga.     

Dissolved carbon dioxide accumulation in a large scale and high density production of TGFβ receptor with baculovirus infected Sf-9 cells

Production of a TGF receptor with high density baculovirus infected Sf-9 cells (7×10⁶cells ml^-1) served as a test run for a retrofitted 150 L microbial fermentor. The entire 110 L batch run was performed in serum free medium, with an addition of a concentrated amino acid and yeastolate mixture at the time of infection. This addition strategy has been proven effective at a small scale by enabling cultures to maintain maximum product yield. In the bioreactor however, while cellular growth was comparable to that of the smaller scale control, TGF receptor production was three fold below the control. To minimize the mechanical stress, low flow rate of pure oxygen was used to control the dissolved oxygen at 40%. As a consequence, it seems that this aeration strategy involved an accumulation of dissolved carbon dioxide that in turn inhibited the protein production. A model has been developed that estimated the CO₂ partial pressure in the culture to be in the vicinity of 0.15 atm. The effect of dissolved CO₂ at this concentration has been assessed at smaller scale for TGF receptor and -gal expression, in controlled atmosphere incubators.Abbreviations CST cumulative sparging time (s) - dpi days post-infection (d) - CO₂/O₂ diffusivities ratio (=0.784 at 27 °C) - DO % saturation of dissolved oxygen (%) - hpi hours post-infection (h) - He Henry coefficient (He_{CO 2}=32.1×10^-3M atm^-1, He_{O 2}=1.23×10^-3 M atm^-1 at 27 °C) - k_La volumetric liquid-side mass transfer coefficient (h^-1) - LDH Lactate dehydrogenase - MOI multiplicity of infection (pfu cell^-1) - N agitation speed (rpm) - OTR oxygen transfer rate (mole O₂ ml^-1 h^-1) - OUR oxygen uptake rate (mole O₂ ml^-1 h^-1) - p partial pressure (atm) - P total pressure (atm) - pfu plaque forming units - q specific consumption or production rate (mole cell^-1 h^-1) - Q_{H, OUT} headspace outlet gas flow rate - Q_S,NOM nominal volumetric sparged gas flow rate (92 ml s^-1 at bioreactor conditions) - R ideal gas constant (82.05 ml atm mole^-1 K^-1) - SR_{V L} molar sparging rate per unit liquid volume (mole ml^-1 h^-1) - SSR specific sparging rate (mole cell^-1 h^-1) - T temperature (C or K) - V_L culture volume (ml) - VVD volume of feed per volume of culture per day (d^-1) - X cell concentration (cell ml^-1) - Y yield coefficient Indexes CO₂, O₂ related to CO₂ or O₂, respectively - glc glucose - H headspace gas phase or gas/liquid interface - L liquid phase - lact lactate - S sparged phase or gas/liquid interface - V viable