cAMP AND cAMP-STIMULATED PROTEIN PHOSPHORYLATION IN ZOOSPORES OF BROWN ALGAE1

Adenosine 3′,5′-cyclic monophosphate (cAMP) and guanosine 3′,5′-cyclic monophosphate (cGMP) were detected at concentrations of 8–11 and 10–20 pmol · mg^?1 protein, respectively, in zoospores of a brown alga, Undaria pinnatifida (Harvey) Suringer. Cellular levels of these cyclic nucleotides did not substantially change during dark to light transition. cAMP-stimulated protein phosphorylation was found in soluble cell-free extracts of zoospores of Undaria pinnatifida and Laminaria angustata Kjellman.     

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.     

PHYSIOLOGICAL INDICATORS OF NUTRIENT DEFICIENCY IN CLADOPHORA (CHLOROPHYTA) IN THE CLARK FORK OF THE COLUMBIA RIVER,MONTANA1

Cellular nutrient concentrations and nutrient uptake rates of Cladophora glomerata (L.) Kuetzing were determined during summer and fall in 1989–1990 at a site on the upper Clark Fork of the Columbia River, Montana. Both physiological tests indicated that Cladophora growth is likely to be limited by nitrogen during late summer-early fall. Maximum uptake rates of ammonia-N and nitrate-N were 5935–6991 and 507–984 μg · g DW^?1· h^?1, respectively, during July–October when dissolved inorganic nitrogen (DIN) concentrations in the river were less than 10 μg · L^?1. During November-December, when DIN was 72–376 μg · L^?1, maximum ammonia-N uptake was 1137–1633 μg · g DW^?1· h^?1 and maximum nitrate-N uptake was 0–196 μg · g DW^?1· h^?1. Cellular nitrogen during summer–early fall was 0.78–1.80% of Cladophora dry weight, frequently at or below 1.1%, a level suggested as a critical minimum N concentration for maximum growth. In contrast, cellular P was 0.18–0.36% of dry weight, 3–6 times the suggested critical P concentration of 0.06%. Molar ratios of cellular N:P (< 16:1) and DIN: SRP (< 4:1) during late summer-early fall also indicated potential N limitation. Cellular N and P from Cladophora collected from a second site influenced by a municipal wastewater discharge in 1990 displayed similar seasonal trends. At both sites, seasonal fluctuations in DIN were closely tracked by changes in cellular N, Cellular P, however, increased through the growing season despite declining levels of SRP in the river.     

Strain‐specific consumption and transformation of alga‐derived dissolved organic matter by members of the Limnohabitans‐C and Polynucleobacter‐B clusters of Betaproteobacteria

We investigated changes in quality and quantity of extracellular and biomass‐derived organic matter (OM) from three axenic algae (genera Rhodomonas, Chlamydomonas, Coelastrum) during growth of Limnohabitans parvus, Limnohabitans planktonicus and Polynucleobacter acidiphobus representing important clusters of freshwater planktonic Betaproteobacteria. Total extracellular and biomass‐derived OM concentrations from each alga were approximately 20 mg l^?1 and 1 mg l^?1 respectively, from which up to 9% could be identified as free carbohydrates, polyamines, or free and combined amino acids. Carbohydrates represented 54%–61% of identified compounds of the extracellular OM from each alga. In biomass‐derived OM of Rhodomonas and Chlamydomonas 71%–77% were amino acids and polyamines, while in that of Coelastrum 85% were carbohydrates. All bacteria grew on alga‐derived OM of Coelastrum, whereas only Limnohabitans strains grew on OM from Rhodomonas and Chlamydomonas. Bacteria consumed 24%–76% and 38%–82% of all identified extracellular and biomass‐derived OM compounds respectively, and their consumption was proportional to the concentration of each OM compound in the different treatments. The bacterial biomass yield was higher than the total identifiable OM consumption indicating that bacteria also utilized other unidentified alga‐derived OM compounds. Bacteria, however, also produced specific OM compounds suggesting enzymatic polymer degradation or de novo exudation.     

Reduction of extracellular dehydroascorbic acid by K562 cells

K562 erythroleukaemic cells produced ascorbate when incubated with dehydroascorbic acid. The reduction depended on the number of cells and on the concentration of dehydroascorbic acid. The observed rate consists of a high affinity (apparent) K_m 7 μM , V_max 3·25 pmol min^?1 (10⁶ cells)^?1 and a low affinity component, which was non-saturable up to 1 mM of DHA (rate increase of 0·1 pmol min^?1 (10⁶ cells)^?1 (1 μM of DHA^?1). The rate was dependent on temperature and was stimulated by glucose and inhibited by phloretin, N-ethylmaleimide, parachloro-mercuribenzoate and thenoyltrifluoroacetone. Although uptake of DHA proceeded at a higher rate than its extracellular reduction, the generation of extracellular ascorbate from DHA cannot be accounted for by intracellular reduction and the release of ascorbate, since the latter was not linear with time and had an initial rate of approximately 3 pmol min^?1 (10⁶ cells^?1). At a concentration of DHA of 100 μM this is 25 per cent of the observed reduction.     

Abundance and primary production of filamentous green algae Zygogonium ericetorum in an extremely acid (pH 2.9) mining lake and its impact on alkalinity generation

1. In extremely acid mining lakes, benthic filamentous green algae (Zygnemataceae, Chlorophyta) thrive as effective competitors for limited carbon (C). These algae could supply C for microbial‐mediated benthic alkalinity generation. However, biomass, productivity and impact of the acidobiontic filamentous green algae at pH ≤3 have not previously been determined. 2. Periphytic filamentous green algae was mapped by harvesting their biomass from 85 1 × 1 m quadrats in mining lake Grünewalder Lauch. Zygogonium ericetorum colonised water depths between 1.6 and 10.5 m covering 88% of total area. Biomass peaked at 5–6 m depth. Total Zygogonium biomass amounted to 72.2 t dry weight for the whole lake (0.94 km²), which corresponds to 16.1 t C and the accumulation of primary production from 2.2 years. 3. Growth of Zygogonium is moderately N, C and extremely P deficient, and seriously stressed by high rates of Fe deposition during summer. Consequently, net primary production (NPP) of Zygogonium, calculated from measured photosynthesis versus irradiance characteristics and calculated underwater irradiance (0.13 g C m^?2 year^?1) and in situ oxygen measurements (7.8 g C m^?2 year^?1), corresponds to only 0.3% and 18.1% of pelagic NPP. 4. Neither pelagic nor benthic Zygogonium primary production can supply enough C for efficient acidity removal. However, at rates of benthic NPP in summer of 21.4 mg C m^?2 day^?1, Zygogonium contributed 26% of the C equivalents to remove acidity associated with ferric iron, contributing at least seasonally to efficient alkalinity generation.     

Evidence of coprophagy in freshwater zooplankton

1. Vertical transport of nutrients in sedimenting faecal material is greatly reduced by coprophageous organisms. Unfortunately, nearly all work on faecal production, sedimentation and coprophagy has dealt with copepods in marine ecosystems. Here, we report the first evidence of coprophagy in freshwater zooplankton from oligotrophic and eutrophic lakes. We used ¹⁴C‐labelled algae and faecal material to estimate the rates of algal clearance and coprophagy. 2. Measured feeding rates per individual on faecal material were similar (Daphnia pulex, D. rosea, Leptodiaptomus tyrelli) or even higher (D. lumholtzi) than filtering rates on phytoplankton. This finding does not necessarily implicate active selection of faeces over algae because: (i) we did not use the same food concentrations for faeces and algae, and (ii) grazers of slightly different sizes were used in each test. 3. Weight‐specific clearance rates of L. tyrelli and Holopedium gibberum on faecal matter (0.084–0.089 mL μg^?1 h^?1) were higher than in the daphniids (0.026 mL μg^?1 h^?1). 4. The data indicate that coprophagy in freshwater ecosystems is an important mechanism of nutrient recycling, and this process should be taken into account when studying nutrient fluxes within lakes and reservoirs.     

Adenylate cyclase and phosphodiesterase activities in relation to a rapid increase in cellular cAMP concentration by hypotonic shock indunaliella viridis

An adenylate cyclase activity of 16.02±1.03 pmol cAMP produced min⁻¹ (mg protein)⁻¹ was detected in a cell homogenate ofDunaliella viridis, a unicellular halotolerant green alga. It was present in both the membrane fraction and soluble fraction separated from the homogenate. Adenylate cyclase activity in the homogenate was activated by 1μM GTPγS but not by Ca²⁺+calmodulin, suggesting this enzyme to be regulated by a G-protein. A phosphodiesterase activity of 23.12±15.03 pmol cAMP decomposed min⁻¹ (mg protein)⁻¹ was found in the homogenate. These activities suggest the presence of a cAMP mediated signal transduction system inDunaliella. Cells, transferred from 1.7 M NaCl medium to 1 M NaCl, showed rapid increase in cAMP within 2 min to about 1.5 times the original concentration (from 2.4±0.2 to 3.9±0.2 pmol per 10⁸ cells) which was recovered in 30 min.     

Photosynthetic characteristics of charophytes from tropical lotic ecosystems

Responses of photosynthetic rates, determined by oxygen evolution using the light and dark bottles technique, to different temperatures, irradiances, pH, and diurnal rhythm were analyzed under laboratory conditions in four charophyte species (Chara braunii Gmelin, C. guairensis R. Bicudo, Nitella subglomerata A. Braun and Nitella sp.) from lotic habitats in southeastern Brazil. Parameters derived from the photosynthesis versus irradiance curves indicated affinity to low irradiances for all algae tested. Some degree of photoinhibition, [β= ‐(0.30–0.13) mg O2 g^?1 dry weight Ir¹ (μmol photons m^?2 s^?1)^?1], low light compensation points (I_c= 4–20 μmol photons m^?2 s^?1) were found for all species analyzed, as well as low values of light saturation parameter (I_k) and saturation (I_s) 29–130 and 92–169 μmol photons m^?2 s^?1, respectively. Photoacclimation was observed in two populations of N. subglomerata collected from sites with different irradiances, consisting of variations in photosynthetic parameters (higher values of a, and lower of I_k and maximum photosynthetic rate, P_max, in the population under lower irradiance). The highest photosynthetic rates for Chara species were observed at 10–15°C, while for Nitella the highest photosynthetic rate was observed at 20–25°C, despite the lack of significant differences among most levels tested. Rates of dark respiration significantly increase with temperature, with the highest values at 25°C. The results from pH experiments showed highest photosynthetic rates under pH 4.0 for all algae, suggesting higher affinity for inorganic carbon in the form of carbon dioxide, except in one population of N. subglomerata, with similar rates under the three levels, suggesting indistinct use of bicarbonate and carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for most algae tested, which was characterized by two peaks: the first (higher) during the morning (07.00–11.00) and the second (lower) in the afternoon (14.00–17.00). This suggests an endogenous rhythm determining the daily variations in photosynthetic rates.     

Evidence that the neuroleptic fluphenazine replaces Ca2+ and adjusts the noradrenaline induced cyclic adenosine monophosphate synthesis in the rat retina

Intact rat retinae were incubated in Krebs-Ringer media with noradrenaline (NA) in the presence (0.75 mM) or absence of extracellular Ca²⁺ and at relatively high (10 mM) or low (1 mM) theophylline concentrations. Depending on the incubation conditions we found that the neuroleptic fluphenazine (FLU) affected cAMP-synthesis separately from cAMP-degradation of the NA-cAMP system in the retina. The main results were: At a relatively high theophylline concentration of 10 mM, where cAMP synthesis alone is operative, and at 0.75 Ca²⁺ we measured with 50 μM NA a NA-response of 110 pmol cAMP/mg prot. At a low theophylline concentration of 1 mM and again at 0.75 mM Ca²⁺ both cAMP-synthesis and -breakdown are operative. In this condition we found the NA-response of 26 pmol cAMP/mg prot. to be raised by 10 μM FLU to 130 pmol cAMP/mg prot. This enhancing effect might be due to inhibition of degradation of NA-induced cAMP by FLU. In the absence of extracellular calcium and again at 10 mM theophylline, 10 μM FLU raised the NA response nearly 4-fold from 42 pmol cAMP/mg prot. to 153 pmol cAMP/mg prot. The lowest effective concentration for obtaining this enhancing effect was 10 μM FLU and the effect is characterized by an apparent K_m of 0.5 μM. The use of 10 mM theophylline in this condition suggests that this FLU-Ca²⁺ effect is confined to the synthesis part of the NA-cAMP system. The effect points to a replacement of an intramembraneous Ca²⁺ function by FLU. In conclusion: our results suggest that FLU inhibits degradation of NA-induced synthesis of cAMP and that the neuroleptic renders the NA-response less dependent on extracellular Ca²⁺.     

Optimization of growth conditions and fatty acid analysis for three freshwater diatom isolates

Diatoms are a group of highly abundant and diverse aquatic algae species. They contain high lipid content along with many bioactive compounds that can be exploited for biotechnological applications. Despite these attractive attributes, diatoms are underrepresented in production projects due to difficulties in their cultivation. To optimize the growth of three freshwater diatom isolates, Cyclotella sp., Synedra sp. and Navicula sp., an orthogonal assay on N, P, Si and Fe, as well as temperature and pH, was designed using traditional single‐factor tests. We also studied the effect of using nanosilica as an alternate Si source on growth and found that the diatom isolates studied achieved their highest growth rates under different combinations of nutrient and environmental conditions. Silica had the greatest influence on growth, followed by phosphate and iron. The optimized growth conditions for Synedra sp. were N: 30 mg L^?1, P: 3 mg L^?1, Si: 14.8 mg L^?1, Fe: 0.448 mg L^?1, temperature 25°C and pH 8. For Navicula sp.: N: 20 mg L^?1, P: 2.5 mg L^?1, Si: 19.7 mg L^?1, Fe: 0.112 mg L^?1, temperature 30°C and pH 7.5–8. For Cyclotella sp.: N: 20 mg L^?1, P: 2.5 mg L^?1, Si: 19.7 mg L^?1, Fe: 0.448 mg L^?1, temperature 30°C and pH 7.5–8. Nano silica negatively affected growth in Navicula sp. and Cyclotella sp., but no such effect was observed in Synedra sp. Fatty acid profiling showed C16:0, C16:1(n ? 7), C18:0 and C20:5(n ? 3) as major fatty acids, with no significant differences in fatty acid methyl ester profiles between traditional and modified media. This work gives us a new insight into the growth requirements of freshwater diatom species, which are less studied than marine species.     

IMPORTANCE OF PHYSICAL VARIABLES ON THE SEASONAL DYNAMICS OF EPILITHIC ALGAE IN A HIGHLY SHADED CANYON STREAM1

The seasonal abundance of epilithic algae was correlated with major physico-chemical parameters in a first-order, heavily shaded stream in northern Arizona. Diatoms made up over 85%, by numerical abundance, of the epilithon community Light energy, water temperature, and stream discharge were most highly correlated with seasonal abundance of epilithic diatom taxa when analyzed with stepwise multiple regression. None of the chemical variables measured in the study (NO₃-N, O-PO₄, SiO₂, including PH) was found to be significantly correlated with the seasonal community structure of epilithic diatoms. Total diatom cell densities showed a significant negative correlation to stream bed light energy. Likewise, total diatom cell densities along a transect in the stream bed showed a negative correlation to current velocity during those months when base flow was low and stable, and current velocity was ≤25 cm·sec-¹. Most diatom taxa had highest cell densities at temperatures < 16°C and at daily mean stream bed light levels < 400 μE·m^?2·s^?1. Highest cell densities of green algae occurred at temperatures between 6–16°C and at daily mean stream bed light levels of > 400 μE·m^?2·s^?1. Blue-green algae (cyanobacteria) grew best at the highest recorded water temperatures and daily mean stream bed light energy (16–20°C and 900–1200 μE·m^?2·s^?1). Abrupt increases in NO₃-N coincided with a brief pulse of Nostoc pruniforme colonies during June, and leaf drop from Alnus oblongifolia during October.     

Implications of rudd (Scardinius erythrophthalmus) herbivory on submerged macrophytes in a shallow eutrophic lake

The role of rudd (Scardinius erythrophthalmus) herbivory was studied in Kirkkojärvi, a shallow and turbid basin in Lake Hiidenvesi, Finland. The submerged species dominating in the rudd diets were Potamogeton obtusifolius, Ranunculus circinatus, Sparganium emersum, bryophytes, and filamentous algae. Plant consumption estimated with bioenergetics modelling increased with fish age, being highest in late summer concomitant with the macrophyte biomass peak. Depending on the age structure, a rudd biomass of 20 kg ha^?1 consumes 18–23 kg of macrophytes ha^?1 a^?1, while a rudd biomass of 100 kg ha^?1 results in plant consumption of 92–115 kg ha^?1 a^?1. Although, rudd seemed to feed rather unselectively on suitable-sized and edible plants, some species abundant in the littoral, such as Myriophyllum verticillatum and pleustophytic Ceratophyllum demersum, were not found in rudd guts, indicating selective plant consumption. In Kirkkojärvi, selective grazing by rudd and increased turbidity and high nutrient levels partly caused by bottom dwelling cyprinid fish, may promote the inedible and pleustophytic macrophytes, which have increased in Kirkkojärvi during the past decades.

     

DIFFERENT RESPONSE MECHANISMS OF TWO PLANKTONIC DESMID SPECIES (CHLOROPHYCEAE) TO A SINGLE SATURATING ADDITION OF PHOSPHATE

Two planktonic algal species, Staurastrum chaetoceras (Schr.) G. M. Smith and Cosmarium abbreviatum Rac. var. planctonicum W. et G. S. West, from trophically different alkaline lakes, were compared in their response to a single saturating addition of phosphate (P) in a P-limited growth situation. Storage abilities were determined using the luxury coefficient R = Q_max/Q₀. Maximum cellular P quotas differed, depending on whether cells were harvested during exponential growth at μ_max (Q_max, R being 26.7 and 9.1 for C. abbreviatum and S. chaetoceras, respectively) or harvested after a saturating pulse at P-limited growth conditions (Q′_max, R being 53.5 and 20.2 for C. abbreviatum and S. chaetoceras, respectively). At stringent P-limited conditions, maximum initial uptake rates were higher in S. chaetoceras than in C. abbreviatum (0.094 and 0.073 pmol P·cell^?1·h^?1, respectively), but long-term (net) uptake rates (over ～20 min) were higher in C. abbreviatum than in S. chaetoceras (0.048 and 0.019 pmol P·cell^?1·h^?1, respectively). Before growth resumed after the onset of a large P addition (150 μmol·L^?1), a lag phase was observed for both species. This period lasted 2–3 days for S. chaetoceras and 3–4 days for C. abbreviatum, corresponding with the time to reach Q^′_max. Subsequent growth rates (over ～10 days) were 0.010 h^?1 and 0.006 h^?1 for S. chaetoceras and C. abbreviatum, respectively, being only 20%–30% of maximum growth rates. In conclusion, S. chaetoceras, with a relatively high initial P-uptake rate, short lag phase, and high initial growth rate, is well adapted to a P pulse of short duration. Conversely, C. abbreviatum, with a high long-term uptake rate and high storage capacity, appears competitively superior when exposed to an infrequent but lasting pulse. These characteristics provide information about possible strategies of algal species to profit from temporarily high P concentrations.     

PRODUCTION AND NUTRIENT REMOVAL BY PERIPHYTON GROWN UNDER DIFFERENT LOADING RATES OF ANAEROBICALLY DIGESTED FLUSHED DAIRY MANURE1

Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. Algal turfs, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 μmol photons·m^?2· s^?1) and anaerobically digested flushed dairy manure wastewater (ADFDMW) loading rates ranging from 0.8 to 3.7 g total N and 0.12 to 0.58 g total P·m^?2·d^?1. Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia, and Cyclotella sp.) partially replaced the filamentous green algae at relatively high ADFDMW loading rates and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6±2.71 to 19.1±2.73 g dry weight· m^?2·d^?1. The N and P content of algal biomass generally increased with loading rate and ranged from 2.9%–7.3% and 0.5%–1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42%–47%). The maximum removal rates of N and P per unit algal biomass were 70 and 13 mg·g^?1 dry weight·m^?2·d^?1, respectively. Recovery of nutrients in harvested algal biomass accounted for about 31%–52% for N and 30%–59% for P. Recovery of P appeared to be uncoupled with N at higher loading rates, suggesting that algal potential for accumulation of P may have already been saturated. It appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the algal turf scrubber units.     

Sulphate transport in the cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. leopoliensis) PCC 7942

Synechococcus R-2 (PCC 1942) actively accumulates sulphate in the light and dark. Intracellular sulphate was 1.35 ± 0.23 mol m^?3 (light) and 0.894 ± 0.152 mol m^?3 (dark) under control conditions (BG-11 media: pH_o, 7.5; [SO₄^2?]_o, 0.304 mol m^?3). The sulphate transporter is different from that found in higher plants: it appears to be an ATP-driven pump transporting one SO₄^2?/ATP [ΔμSO₄^2?_i,o=+ 27.7 ± 0.24 kJ mol^?1 (light) and + 24 ± 0.34 kj mol^?1 (dark)]. The rate of metabolism of SO₄^2?at pH_o, 7.5 was 150 ± 28 pmol m^?2 s^?1 (n = 185) in the light but only 12.8 ± 3.6 pmol m^?2 s^?1 (n = 61) in the dark. Light-driven sulphate uptake is partially inhibited by DCMU and chloramphenicol. Sulphate uptake is not linked to potassium, proton, sodium or chloride transport. The alga has a constitutive over-capacity for sulphate uptake [light (n= 105): K_m= 0.3 ± 0.1 mmol m^?3, V_max, = 1.8 ± 0.6 nmol m^?2 s^?1; dark (n= 56): K_m= 1.4 ± 0.4 mmol m^?3, V_max= 41 ± 22 pmol m^?2 s^?1]. Sulphite (SO₃^2?) was a competitive inhibitor of sulphate uptake. Selenate (SeO₄^2?) was an uncompetitive inhibitor.     

Feeding and growth of Asellus aquaticus (Isopoda) on food items from the littoral of Windermere, including green leaves of Elodea canadensis

SUMMARY. In the laboratory, Asellus aquaticus devoured intact green leaves from growing shoots of the aquatic macrophyte Elodea canadensis. In four collections of A. aquaticus on Elodea in a lake (Windermere), c. 20% of the specimens contained in their guts fragments of green Elodea leaves; this material and pieces of oak (Quercus) were identified from characteristic leaf hairs. Some specimens had also eaten the filamentous alga Oedogonium. Fluorescence microscopy is a useful aid for screening invertebrates that may have eaten living plant tissues. Immature A. aquaticus, with an initial mean body length of c. 3 mm, wet weight c. 1 mg, were grown through sexual maturity over a 49-day period at 15°C in a series of twenty-two experiments (six to twelve isolated specimens in each experiment) comparing growth rates on different foods, including instances where no food was given. Animals were fed on a variety of items collected from the littoral of Windermere, plus some laboratory cultures of algae and bacteria. The highest mean specific growth rate (5.8% day^?1) was obtained on young Elodea leaves mechanically shaken to remove epiphytes. Other diets yielding fast growth rates (3.7–5.3% day^?1) were young growing leaves of Elodea with few epiphytes and older green and brown living leaves covered with a thick growth of epiphytic algae, epiphytic algae removed from Elodea, plastic imitation Elodea immersed in the lake until covered with attached algae, epilithic algae on stones, Oedogonium, and decaying oak leaves. Slower growth (1.3–2.2% day^?1) and poorer survival was obtained on the following: a pure culture of the bacterium Sphaerotilus natans; cultured bacteria from lakewater; the filamentous algae Cladophora and Stigeoclonium both with and without epiphytes; faecal matter from Asellus; freshly killed Asellus; lake sediment. Some growth (mean = 0.7% day^?1) and 50% survival for 21 days occurred in ‘starved’ animals kept in filtered, sterilized lakewater. Better survival and slightly faster growth (1.0–1.5% day^?1) occurred in ‘starved’ animals kept in filtered and unfiltered lakewater. Growth of A. aquaticus was also experimentally determined from birth in animals fed on young green Elodea leaves and on decaying oak leaves. On both diets, growth was curvilinear and approximately exponential from birth to sexual maturity reached at c. 2mg wet weight in 46–60 days at 15°C. In older specimens the relative growth rate gradually fell over a period of 50 days, representing a more linear phase of growth during sexual maturity.     

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.     

BIOSYNTHESIS OF POLY‐3‐HYDROXYBUTYRATE (PHB) IN THE TRANSGENIC GREEN ALGA CHLAMYDOMONAS REINHARDTII1

A cell‐wall deficient strain of Chlamydomonas reinhardtii P. A Dang. CC‐849 was cotransformed with two expression vectors, p105B124 and pH105C124, containing phbB and phbC genes, respectively, from Ralstonia eutropha. The transformants were selected on Tris‐acetate‐phosphate media containing 10 μg · mL^?1 Zeomycin. Upon further screening, the transgenic algae were subcloned and maintained in culture. PCR analysis demonstrated that both phbB and phbC genes were successfully integrated into the algal nuclear genome. Poly‐3‐hydroxybutyrate (PHB) synthase activity in these transgenic algae ranged from 5.4 nmol · min^?1 · mg protein^?1 to 126 nmol · min^?1 · mg protein^?1. The amount of PHB in double transgenic algae was determined by gas chromatography–mass spectrometry (GC–MS) when comparing with PHB standard. In addition, PHB granules were observed in the cytoplasm of transgenic algal cells using TEM, which indicated that PHB was synthesized in transgenic C. reinhardtii. Hence, results clearly showed that producing PHB in C. reinhardtii was feasible. Further studies would focus on enhancing PHB production in the transgenic algae and targeting the chloroplast for PHB accumulation.