ADAPTATION OF THE UNICELLULAR ALGA DUNALIELLA PARVA TO A SALINE ENVIRONMENT1

The holophilic alga Dunaliella parva produces glycerol as a major product of photosynthetic ¹⁴CO₂ incorporation and accumulates very large amounts of intracellular glycerol. A method was adopted for the determination of the cell water space based on the distribution of ¹⁴C sorbitol and ³H₂O between the cells and the medium. Using these measurements the internal concentration of glycerol was found to be isoomotic with that of the medium over a broad range of 0.6 to 2.1 m NaCl. When the extracellular salt concentration of an algal suspension was increased or decreased, the intracellular water content immediately varied so as to keep an osmotic equilibrium between the cells and the medium. During the following 90 min under metabolic conditions, glycerol content changed until a new level was reached. Since no leakage of intracellular glycerol was observed above 0.6 m NaCl, these alterations in glycerol content are interpreted as due to metabolic formation and degradation of intracellular glycerol. Determination of the glycerol sensitivity of enzymic and photosynthetic reactions of cell-free preparations from D. parva showed a broad range of tolerance to high concentrations of glycerol. These results indicate that osmoregulation in Dunaliella depends on the synthesis or degradation of intracellular glycerol in response to the external salt concentration. A proposed scheme of glycerol synthesis in Dunaliella is suggested.     

PHYSIOLOGICAL ECOTYPES IN THE MARINE ALGA BOSTRYCHIA RADICANS (CERAMIALES,RHODOPHYTA) FROM THE EAST COAST OF THE U.S.A1

The comparative ecophysiology of nine culture isolates of the eulittoral red alga Bostrychia radicans (Montagne) Montague collected at sites from seven states along the east coast of the U.S.A. was investigated. The growth response in relation to different salinity and light conditions as well as photosynthesis-irradiance curves were studied. In addition, the effect of salt treatment on the content of the isomeric polyols d -sorbitol and d -dulcitol was also studied. All isolates grew between salinities of 5.3 and 70 ppt but with quite different optima and maxima. The isolates were all adapted to low light levels, i.e. growth was already recorded at 2.5 μmol photons·m^?2·s^?1, and growth rates peaked between 40 and 60 μmol photons·m^?2·s_-1. These low-light requirements were also reflected by the photosynthesis-irradiance curves: all plants had low light compensation points (2.5–9.7 μmol photons ·m^?2·^?1) and low photon fluence rates for initial saturation of photosynthesis (38.1–84.7 μmol photons·m^?2·s^?1, indicating that these isolates are “shade-adapted.” Isolates from Florida and Georgia synthesized and accumulated both the osmolytes d -sorbitol and d -dulcitol in increasing salinities, whereas only d -sorbitol was present in plants from North Carolina north to Connecticut. d -sorbitol was always strongly involved in osmotic acclimation. In various isolates from the same location in South Carolina, both polyol patterns were found, i.e. d -sorbitol plus d -dulcitol and d -sorbitol only. All data indicate that B. radicans exhibits a broad salinity tolerance and a low-light preference, which explain the successful colonization of this alga on various intertidal and shaded substrates. The data also clearly indicate intraspecific differences among the nine isolates, which is interpreted as development of different physiological ecotypes.     

THE EFFECT OF SULFIDE ON THE BLUEGREEN ALGAE OF HOT SPRINGS. I. NEW ZEALAND AND ICELAND1

The concentration of soluble sulfide (H₂S, HS^?, S⁼)² in hot springs of New Zealand and Iceland has a “species-determining” effect which appears to override the effect of all other chemical factors excepting hydrogen ion concentration. The cosmopolitan high-temperature form (HTF) of Mastigocladus laminosus (Ag.) Cohn appears to be sensitive to concentrations of S⁼ over 0.15 mg·l^?1 in New Zealand and 0.25 mg·l^?1 in Iceland. It was absent in thermal streams where S⁼ level was high enough to exceed this concentration at a point below its optimal temperature range (i.e., below ca. 50 C). In low or non-S⁼ springs in these regions this alga formed mats to an upper temperature limit of 63–64 C. In contrast, one bluegreen alga (Oscillatoria amphigranulata van Goor) occurred abundantly only in moderate to high S⁼ springs of New Zealand; this was a species with an upper temperature limit of about 57 C. Field ¹⁴C-HCO₃^? incorporation experiments with various levels of added S⁼ confirmed the sensitivity of HTF Mastigocladus and the great tolerance of O. amphigranulata. In the latter, the photosynthetic incorporation of ¹⁴C-HCO₃^? was sustained or enhanced by the additions of S⁼ in the presence of 5 × 10^?5m DCMU, an inhibitor of photoelectron transport on the reducing side of photosystem II. It is possible, but not proven, that S⁼ may act as a photoreductant in this species.     

PHOSPHORUS UPTAKE KINETICS OF SPIROGYRA FLUVIATILIS (CHAROPHYCEAE) IN FLOWING WATER1,2

The inorganic phosphorus (P_i) uptake kinetics of Spirogyra fluviatilis Hilse were examined as a function of phosphorus cell quota (Q^P) and flow velocity in a laboratory stream apparatus. Short-term uptake and the acclimation of the uptake mechanism to flow were measured by the disappearance of P_i pulses in a recirculating flow cell. Short-term P_i uptake was biphasic. When the alga was P-deficient, Phase 1 and 2 half-saturation constants and maximum uptake rates were 11.0 and 47.2 μg P·L^?1 and 473 and 803 μg P·g dry wt^?1 h^?1, respectively. Flowing water altered short-term uptake when the alga was P-deficient, but not when it was P-replete. When Q^P was less than 0.21%, increases in flow velocity from 3 to 15 cm·s^?1 enhanced uptake with maximum uptake for any P_i pulse at 12 and 15 cm·s^?1. At 22 and 30 cm·s^?1, uptake was reduced by 12% or more relative to the maxima. If, however, the alga was cultivated at 22 and 30 cm·s^?1 and short-term P_i uptake was measured at 12 cm·s^?1, uptake was on average 33% greater than when the alga was cultivated at the latter velocity. Apparently, the alga could adjust short-term uptake to compensate for the suboptimal conditions of the faster velocities. Long-term P_i uptake and net phosphorus efflux were estimated by a non-steady state application of the Droop equation. Long-term uptake of very low P_i concentrations was not reduced by fast flowing water. Instead, uptake increased proportionately with flow velocity. Maximum phosphorus efflux from S. fluviatilis was 3% of cellular P per hour and occurred when Q^P was greater than 0.2%. At lower Q^P, the hourly efflux rate was typically less than 1%. Flowing water did not greatly enhance efflux, although when P_i was undetectable, efflux did tend to increase slightly with velocity. The data show that the effects of flowing water on P_i uptake were varied and not always beneficial. If the effects of flowing water on nutrient acquisition by other lotic algae are similarly varied and complex, flow may be an important determinant of nutrient partitioning among benthic algae in streams.     

The effects of sodium chloride,potassium chloride and glycerol on the activity of nitrate reductase of a salt-tolerant and two non-tolerant plants

Summary The activity of nitrate reductase from the salt-tolerant alga Dunaliella parva is inhibited by sodium chloride and potassium chloride, but not by glycerol. The activity of the enzyme from Chlorella pyrenoidosa Chick 611-8b and from the XD line of tobacco (Nicotiana tabacum L. cv. Xanthi) cells is inhibited by all three solutes. Salt tolerance in Dunaliella parva, which is due to internal formation of glycerol, is accompanied by the adaptation of the activity of the enzyme to elevated glycerol concentrations.     

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.     

SPECIES-SPECIFIC CHARACTERISTICS EXPLAIN THE PERSISTENCE OF STIGEOCLONIUM TENUE (CHLOROPHYTA) IN A WOODLAND STREAM1

The heterotrichous alga Stigeoclonium tenue Küetzing is dominant in many streams with high densities of herbivores. Previous in situ studies in Walker Branch (WB), a woodland stream in eastern Tennessee, indicated that dominance by Stigeoclonium basal cells was “grazer-dependent”; however, Stigeoclonium also appeared to have a lower biomass–specific productivity rate than other species that dominated when snails were experimentally removed. Here, an explicit test of the grazing dependence of Stigeoclonium was made with unialgal cultures established in the laboratory. Five different “assemblage types” were tested: 1 and 2) unialgal cultures of Stigeoclonium at low and high biomass, 3 and 4) a mixed assemblage of diatoms at low and high biomass, and 5) a natural stream community. Reduction in chlorophyll a after exposure to snail grazing was dependent on assemblage type (one-way ANOVA, P < 0.0001); low biomass Stigeoclonium tiles and tiles from the stream (on which basal cells of Stigeoclonium were dominant) were most grazer-resistant. In addition, Stigeoclonium had a lower biomass-specific productivity rate (measured as H¹⁴CO₃^? uptake) than a mixed assemblage of diatoms, regardless of biomass level, suggesting an underlying tradeoff between resistance to herbivory and competitive ability. Additional laboratory experiments were conducted to determine the response of Stigeoclonium to high (approx. 150 μmol quanta ·m^?2· s^?1)and low (approx. 25 μmol quanta · m^?2· s^?1) irradiance when nutrients were at 1) ambient WB concentrations and 2) increased 1000× ambient concentrations. There was a positive response of growth to increased irradiance only under high nutrient conditions. This suggests that observed reductions in the abundance of Stigeoclonium under high irradiance/low nutrient conditions that occur on a seasonal basis in WB can be explained in part by autecological resource requirements of this alga. We use these results to model the response of algal communities dominated by basal-regenerating species (e.g. Stigeoclonium) to gradients in herbivory and productivity. The results of our culture studies, combined with an overview of factors affecting communities dominated by grazer-resistant species, illustrate how both broad-scale (e.g. functional form) and species-specific studies can be combined to achieve an understanding of community dynamics.     

Movement of Abscisic Acid Across the Plasmalemma and the Tonoplast of Guard Cells of Valerianella locusta

Uptake experiments and efflux compartmental analyses of abscisic acid (ABA) with acid treated epidermal peels of Valerianella locusta were performed to elucidate the mechanisms of transport of ABA across the plasmalemma and tonoplast of guard cells. ABA uptake across the plasmalemma is linearly correlated with external ABA concentration in the incubation medium. Under alkaline conditions ABA-uptake was not significantly above background, indicating that ABA uptake occurs mainly by diffusion of undissociated ABAH as the most permeable species, which is trapped afterwards in the alkaline cytosol as impermeable ABA^?. Efflux analysis of ABA revealed a saturable component of ABA transfer across the tonoplast. A Woolf-Augustinsson-Hofstee analysis suggested the existence of two transport systems for ABA at the tonoplast. The high affinity transport system had a K_M of 0.21 mol m^?3 and a V_max 85.8 amol ABA cell^?1 h^?1. Using the data of the uptake and efflux experiments we calculated the permeability coefficients of ABA for the plasmalemma and the tonoplast of guard cells, which are 2.46 10^?7 m s–¹ and 1.26 10^?8m s^?1, respectively. The distribution of the pH-probe (¹⁴C)-DMO between medium, cytosol and vacuole was investigated and used to calculate cytosolic and vacuolar pH. The vacuolar pH is too low to explain the high vacuolar ABA concentration by trapping of ABA^?, whereas the cytosol is sufficiently alkaline to act as an efficient anion trap. Therefore we conclude that ABA transport across the guard cell tonoplast is catalyzed by a saturable uptake component.     

EFFECTS OF HARVEST STAGE AND LIGHT ON THE BIOCHEMICAL COMPOSITION OF THE DIATOM THALASSIOSIRA PSEUDONANA1

The marine diatom Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal was cultured under three different light regimes: 100 μmol photon · m^?2· s^?1 on 12:12 h light : dark (L:D) cycles; 50 μmol photon · m^?2· s^?2 on 24:0 h L:D; and 100 μmol photon · m^?2· s^?1 on 24:0 h L:D. It was harvested during logarithmic and stationary phases for analysis of biochemical composition. Across the different light regimes, protein (as % of organic weight) was highest in cells during logarithmic phase, whereas carbohydrate and lipid were highest during stationary phase. Carbohydrate concentrations were most affected by the different light regimes; cells grown under 12:12 h L:D contained 37–44% of the carbohydrate of cells grown under 24:0 h L:D. Cells in logarithmic phase had high proportions of polar lipids (79 to 89% of total lipid) and low triacylglycerol (≤10% of total lipid). Cells in stationary phase contained less polar lipid (48 to 57% of total lipid) and more triacylglycerol (22 to 45% of total lipid). The fatty acid composition of logarithmic phase cells grown under 24:0 h L:D were similar, but the 100 μmol photon · m^?2· s^?1 (12:12 h L:D) cells at the same stage contained a higher proportion of polyunsaturated fatty acids (PUFAs) and a lower proportion of saturated and monounsaturated fatty acids due to different levels of 16:0, 16:1(n-7), 16:4(n-1), 18:4(n-3), and 20:5(n-3). With the onset of stationary phase, cells grown at 100 μmol photon · m^?2· s^?1 (both 12:12 and 24:0 h L:D) increased in proportions of saturated and monounsaturated fatty adds and decreased in PUFAs. Concentrations (% organic or dry weight) of 14:0, 16:0, 16:1(n-7), 20:5(n-3), and 22:6(n-3) increased in cells of all cultures during stationary phase. The amino acid compositions of cells were similar irrespective of harvest stage and light regime. For mariculture, the recommended light regime for culturing T. pseudonana will depend on the nutritional requirements of the animal to which the alga is fed. For rapidly growing bivalve mollusc larvae, stationary-phase cultures grown under a 24:0 h L:D regime may provide more energy by virtue of their higher percentage of carbohydrate and high proportions and concentrations of energy-rich saturated fatty acids.     

PHYSIOLOGICAL CHARACTERISTICS OF PHOTOSYNTHESIS IN PORPHYRIDIUM CRUENTUM: EVIDENCE FOR BICARBONATE TRANSPORT IN A UNICELLULAR RED ALGA1

Various physiological characteristics of photosynthesis in the unicellular red alga Porphyridium cruentum Naegeli have been investigated. The rate of photosynthesis was optimal at 25° C and pH 7.5 and was not inhibited by 21% oxygen over a temperature range of 5 to 35° C. Kinetics of whole cell photosynthesis as a function of substrate concentration gave a K_1/2, (CO₂) of 0.3 μM. CO₂ compensation point, measured in a closed system at pH 7.5, was a constant 6.7 m?L · L^?1 over the temperature range 15 to 30° C and was unaffected by O₂ concentration. Whole cell photosynthesis, measured in a closed system at alkaline pH, showed that the rates of oxygen evolution were greatly in excess of the rate of CO₂ supply from the spontaneous dehydration of HCO₃^? in the medium. This indicates that bicarbonate is utilized by the cell to support this photosynthetic rate. These physiological characteristics of Porphyridium cruentum are consistent with the hypothesis that this alga transports bicarbonate across the plasmalemma.     

Net efflux of Cl− during hypotonic turgor regulation in a brackish water alga Lamprothamnium*

Abstract. Net efflux of Cl^? was measured potentiometrically (Ag/AgCl electrode) during turgor regulation which was induced by hypotonic treatment (hypotonic turgor regulation) in the alga Lamprothamnium succinctum. The efflux of Cl^? reached the peak value (11 μmol m ^?2s^?1) several minutes after the hypotonic treatment was started and then declined. The efflux of Cl^? and inhibition of the cytoplasmic streaming [reflection of an increase in cytoplasmic concentration of free Ca²⁺([Ca²⁺]_c)] were blocked under a low external concentration of Ca²⁺ ([Ca²⁺]_e) (0·01 mol m^?3) and resumed after raising [Ca²⁺]_e to the normal value (3·9 mol m^?3). The decrease in cell-osmotic pressure upon hypotonic treatment was inhibited by lowering either turgor pressure or [Ca^2h]_e. The inhibition was reflected in decreases of both the efflux of Cl^? and the membrane conductance. Recovery of the cytoplasmic streaming from the inhibition was also accelerated by the same treatments. It is concluded that an increase in turgor pressure is continuously sensed by the cells and that continuous presence of external Ca²⁺ is necessary for the hypotonic turgor regulation.     

EFFECT OF LIGHT QUALITY AND INTENSITY ON GLYCEROL CONTENT IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE) AND THE RELATIONSHIP TO CELL GROWTH/OSMOREGULATION1

Dunaliella tertiolecta Butcher was grown at two intensities (33, 150μEin · m^?2· s^?1) of blue light and white light at 0.25, 0.50 and 1.00 M NaCl. Growth rates were used as an indication of the relative osmoregulatory ability of cells in the various treatments. There was no significant effect on growth rate due to various NaCl molarities. No significant difference in growth rate was found between blue- and white-light cultures at the high intensity, the average growth constant being 2.07 divisions/day. However, at the low intensity illumination, blue light produced a significant increase in growth rate; 1.42 vs. 0.93 divisions/day for blue light and white light grown cells respectively. The average glycerol content of exponentially dividing cells grown at 0.25, 0.50 and 1.00 M NaCl was 0.12, 0.41 and 1.12 mg/10⁸ cells, respectively, as measured by gas chromatography. The intracellular glycerol content was significantly reduced by blue light at both light intensities and at each NaCl molarity. However, high light intensity reduced cellular glycerol content more than the reduction effected by blue light. Glycerol accumulated in the medium throughout culture growth. Intracellular glycerol content also increased with cellular aging reaching 2.72 mg/10⁸ cells in stationary phase, low intensity 1.00 M NaCl cultures. A negative correlation between glycerol content and growth rate was found. Total inhibition of glycerol production could not be obtained by treatment with blue light. However, this negative correlation possibly indicates that D. tertiolecta expends energy producing an excess amount of glycerol over that required for osmoregulation, leading to a reduction in the growth rate for the organism.     

THE INABILITY OF THE TEXAS “BROWN TIDE” ALGA TO USE NITRATE AND THE ROLE OF NITROGEN IN THE INITIATION OF A PERSISTENT BLOOM OF THIS ORGANISM1

A planktonic alga similar in general morphology and pigments to Aureococcus anophagefferens Hargraves and Sieburth has caused persistent and ecologically damaging blooms along the south Texas coast. Experiments using 100 μM NO₃^?, NO₂^?, and NH₄⁺ demonstrated that the alga could not use NO₃^? for growth but could use NO₂^? and NH₄⁺. Doubling iron or trace metal concentrations did not permit growth on NO₃^?. Chemical composition data for cultures grown in excess NO₃^? or NH₄⁺, respectively, were as follows: N·cell^?1 (0.88 vs. 1.3 pg), C:N ratio (25:1 vs. 6.4:1), C:chlorophyll a (chl a) (560:1 vs. 44:1), and chl a·cell^?1 (0.033 vs. 0.16 pg). These data imply that cells supplied with NO₃^? were N-starved. Culture addition of 10 mM final concentration chlorate (a nitrate analog) did not affect the Texas isolate while NO₃^? utilizing A. anophagefferens was lysed, suggesting that the NO₃^? reductase of the Texas isolate is nonfunctional. Rates of primary productivity determined during a dense bloom indicated that light-saturated growth rates were ca. 0.45 d^?1, which is similar to maximum rates determined in laboratory experiments (0.58 d^?1± 0.16). However, chemical composition data were consistent with the growth rate of these cells being limited by N availability (C:N 28, C:chl a 176, chl a·cell^?1 0.019). Calculations based on a mass balance for nitrogen suggest that the bloom was triggered by an input of ca. 69 μM NH₄⁺ that resulted from an extensive die-off of benthos and fish.     

ADSORPTION AND UPTAKE OF COPPER BY THE GREEN ALGA SCENEDESMUS SUBSPICATUS (CHLOROPHYTA)1

Copper (II) accumulation has been investigated in the green alga Scenedesmus subspicatus G. Brinkmann considering both adsorption and uptake kinetics. Experiments were conducted in a Cu- and PH-buffered medium at different free Cu²⁺ concentrations that were neither growth limiting nor toxic. We distinguished between adsorption on the cell surface and intracellular uptake by extracting copper from the cells with EDTA. Data from short-term experiments were compared with data obtained from experiments under steady state conditions. The accumulation of Cu can be described by two processes, an initial fast adsorption occurring within a minute followed by a slower intracellular uptake. Metal uptake followed Michaelis-Menten kinetics and is mediated by two systems, one with low and the other with high affinity. The maximum uptake rates (1.30 × 10^?-¹⁰ mol·[g dry wt algae]^?1· min^?1, 3.67 × 10^?-⁹ mol·[g dry wt algae]^?1·min^?1), and the half-saturation constants (6.84 × 10^?-¹⁴ M, 2.82 × 10^?-¹² M) for the two uptake systems were determined using the Lineweaver-Burk plot. The calculated maximum concentration of binding sites on the surface of the algae is initially higher (9.0 × 10^?-⁶ mol Cu.[g dry wt algae]^?1) than under steady state conditions (2.9 × 10^?-⁶ mol Cu·[g dry wt algae]^?1). This suggests that the initial binding to the algal surface comprises the binding to specific transport ligands as well as to inert adsorption sites. The conditional stability constant of the Cu binding to surface ligands was calculated as log K_Cu= 11.0 at pH 7.9. This freshwater alga has a high ability to accumulate Cu, reflecting its adaptation to the bioavailable concentration of copper.     

A novel bioreactor for immobilized phototrophs

A novel configuration of photobioreactor is described in which filaments of alginate containing immobilized cells of a leaky mutant of Dunaliella parva are wound round a central light well which is located within a glass outer chamber so that a liquid medium is caused to flow in the annular space between the outside chamber and the alginate filaments. Glycerol production by D. parva was maintained for 700 h and the highest concentration of glycerol attained was approx. 12 mg l⁻¹.     

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.     

EFFECT OF TEMPERATURE AND IRRADIANCE ON GROWTH OF HAEMATOCOCCUS PLUVIALIS (CHLOROPHYCEAE)1

The growth characteristics of Haematococcus pluvialis Flotow were determined in batch culture. Optimal temperature for growth of the alga was between 25° and 28°C, at which the specific growth rate was 0.054 h^?1. At higher temperatures, no cell division was observed, and cell diameter increased from 5 to 25 μm. The saturated irradiance for growth of the alga was 90 μmol quanta · m^?2·s^?1; under higher irradiances (e.g. 400 μmol quanta·m^?2·s^?1) astaxanthin accumulation was induced. Growth rate, cell cycle, and astaxanthin accumulation were significantly affected by growth conditions. Careful attention should be given to the use of optimal growth conditions when studying these processes.     

METHYLAMINE UPTAKE IN THE GREEN ALGA CHLORELLA PYRENOIDOSA1

Methylamine uptake in nitrogen-starved Chlorella pyrenoidosa Beij. follows Michaelis-Menten kinetics: maximum uptake is about 1.6 nmol μl^?1· cells · min^?1, half-saturation occurs at 4 μM methylamine, and the slope in the range where uptake is proportional to concentration is 0.4 nmol μl^?1· min^?1·μM^?1. In cells grown in the presence of a non-limiting nitrogen concentration, methylamine uptake is directly proportional to concentration up to at least 0.5 mM, and the slope is 1/500 that for starved cells. Similar uptake kinetics have been reported for Penicillium chrysogenum and attributed to an inducible “ammonium permease.” Apparently, a similar permease occurs in algae.     

ANALYSIS OF THE EXPRESSION OF GENES FOR P-TYPE ATPASE IN THE HALOTOLERANT ALGA DUNALIELLA SALINA (CHLOROPHYCEAE)1

A partial complementary DNA (cDNA) (DSA8) for a P-type ATPase was obtained from the halotolerant alga Dunaliella salina (Dunal) Teod. (Chlorophyceae). The cDNA exhibited greater than 90% homology to the cDNA for a H⁺-ATPase in D. bioculata Butcher. The expression of the gene that corresponded to DSA8 was decreased strongly by increases in NaCl concentration. The expression of a gene that corresponded to another ATPase (DSA1; possibly for a Ca²⁺-ATPase) from D. salina did not show the same decrease as did the DSA8. However, increased osmotic pressure due to glycerol resulted in the same decrease in the DSA8 gene. Under salt or osmotic stress, the activity of a H⁺-ATPase from microsomes of this alga also decreased. We suggest that expression of the gene for the plasma membrane H⁺-ATPase of D. salina is regulated by osmotic pressure rather than by the concentration of NaCl.