Characterization of phosphate absorption in maize root cortex segments

Uptake of phosphate ions by 1 mm segments of isolated maize root cortex layers was studied. Cortex segments (from roots of 8 days old maize plants) absorb phosphate ions from 1 mM KH₂PO₄ in 0.2 mM CaSCO₄ at the average rate of 34.3 ±3.2 μg P_i g^?1 (fr. m.) h^?1,i.e. 0.35± 0.02 μmol P_i g^?1 (fr. m.) h^?1. Phosphate uptake considerably increases after a certain period of “augmentation”,i.e. washing in aerated 0.2 mM CaSO₄. This increase is completely blocked by the presence of 10 μg ml^?1 cycloheximide. The relation of uptake rate to phosphate concentration in the medium was shown to have 3 phases in the concentration range of 0.02 - 40 mM. Transition points were found between 0.8–1 mM and 10–20 mM. Following K_m and V_max values were found: K_m[mM] : 0.37 - 3.82 - 27.67 V_max[μg P_i g^?1 (fr. m.) h^?1] : 3.33 - 39.40 - 66.67 We have found no sharp pH optimum for phosphate uptake. It proceeds at almost constant rate till pH 6.0 and then the uptake rate drops with increasing pH. At low phosphate concentrations (1 mM) the lowest uptake rate was found at 5 and 13 °C, while the uptake is higher at 5 °C than at 13 °C at phosphate concentrations higher than 1 mM. At these concentrations uptake rate at 35 °C is lower than at 25 °C. Phosphate uptake considerably decreased in anaerobic conditions. DNP and iodoacetate (0.1 mM) completely blocked phosphate uptake from 1 mM KH₂PO₄, while uptake from 5 and 10 mM KH₂PO₄ was left unaffected by these substances. The inhibitors of active - SH groups NEM and PCMB inhibited phosphate uptake: 10^?3 M NEM by 81.6%, 10⁴ M NEM by 42% and 10^?4 M PCMB by 42%.     

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.     

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.     

The steady-state rate of ATP synthesis in the perfused rat heart measured by 31P NMR saturation transfer

The steady-state rate of ATP synthesis in the isolated, Langendorff-perfused rat heart was determined using a ³¹P NMR saturation transfer method. At 37°C and a perfusion pressure of 70 cm H₂O the value is 2.8 ± 0.3 (n=5 ± S.E.M.) μmol.s^?1. (g. dry wt.)^?1. The activity of creatine phosphokinase measured in the same experiments was 14.6 ± 1.0 μ mol.s^?1 .(g. dry wt.)^?1. From the rate of ATP synthesis and the separately measured oxygen consumption we calculated an apparent mitochondrial ADP:O ratio of 3.5 ± 0.8 in the intact tissue.     

PHYSIOLOGICAL RESPONSES OF ANABAENA VARIABILIS (CYANOPHYCEAE) TO INSTANTANEOUS EXPOSURE TO VARIOUS COMBINATIONS OF LIGHT INTENSITY AND TEMPERATURE1

Light intensity and temperature interactions have a complex effect on the physiological process rates of the filamentous bluegreen alga Anabaena variabilis Kütz. The optimum temperature for photosynthesis increased with increasing light intensity from 10°C at 42 μE·m^?2·s^?1 to 35°C at 562 μE·m^?2·s^?1. The light saturation parameter, I_K, increased with increasing temperatures. The maximum photosynthetic rate (2.0 g C·g dry wt.^?1·d^?1) occurred at 35°C and 564 μE·m^?2·s^?1. At 15°C, the maximum rate was 1.25 g C·g dry wt.^?1·d^?1 at 332 μE·m^?2·s^?1. The dark respiration rate increased exponentially with temperature. Under favorable conditions of light intensity and temperature the percent of extracellular release of dissolved organic carbon was less than 5% of the total C fixed. This release increased to nearly 40% under combinations of low light intensity and high temperature. A mathematical model was developed to simulate the interaction of light intensity and temperature on photosynthetic rate. The interactive effects were represented by making the light-saturation parameters a function of temperature.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.     

SHORT‐TERM EFFECT OF TEMPERATURE ON THE PHOTOKINETICS OF MICROALGAE FROM THE SURFACE LAYERS OF ANTARCTIC PACK ICE1

Microalgae growing within brine channels (85 psu salinity) of the surface ice layers of Antarctic pack ice showed considerable photosynthetic tolerance to the extreme environmental condition. Brine microalgae exposed to temperatures above ?5°C and at irradiances up to 350 μmol photons·m^?2·s^?1 showed no photosynthetic damage or limitations. Photosynthesis was limited (but not photoinhibited) when brine microalgae were exposed to ?10°C, provided the irradiance remained under 50 μmol photons·m^?2·s^?1. The highest level of photosynthetic activity (maximum relative electron transport rate [rETR_max]) in brine microalgae growing within the surface layer of sea ice was at approximately 18 μmol electrons·m^?2·s^?1, which occurred at ?1.8°C. Effective quantum yield of PSII and rETR_max of the halotolerant brine microalgae exhibited a temperature‐dependent pattern, where both parameters were higher at ?1.8°C and lower at ?10°C. Relative ETR_max at temperatures above ?5°C were stable across a wide range of irradiance.     

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.     

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.     

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.     

Temperature-jump kinetics of the dC-G-T-G-A-A-T-T-C-G-C-G double helix containing a G . T base pair and the dC-G-C-A-G-A-A-T-T-C-G-C-G double helix containing an extra adenine

The kinetics of helix formation were investigated using the temperature-jump technique for the following two molecules: dC-G-T-G-A-A-T-T-C-G-C-G, which forms a double helix containing a G·T base pair(the G·T 12-mer), and dC-G-C-A-G-A-A-T-T-C-G-C-G, which forms a double helix containing an extra adenine (the 13-mer). When data were analyzed in an all-or-none model, the activation energy for the helix association process was 22 ± 4 kcal/mol for the G·T 12-mer and 16 ± 7 kcal/mol for the 13-mer. The activation energy for the helix-dissociation process was 68 ± 2 kcal/mol for the G·T 12-mer and 74 ± 3 kcal/mol for the 13-mer. Rate constants for recombination were near 10⁵s^?1M^?1 in the temperature range from 32 to 47°C; for the dissociation process, the rate constants varied from 1s^?1 near 32°C to 130s^?1 near 47°C. Possible effects of hairpin loops and fraying ends on the above data are discussed.     

The effect of acute high light and low temperature stresses on the ascorbate–glutathione cycle and superoxide dismutase activity in two Dunaliella salina strains

Dunaliella species accumulate carotenoids and their role in protection against photooxidative stress has been investigated extensively. By contrast, the role of other antioxidants in this alga, has received less attention. Therefore, the components of the ascorbate–glutathione cycle, along with superoxide dismutase (E.C. 1.15.1.1) and peroxidase (E.C. 1.11.1.11) activity were compared in two strains of Dunaliella salina. Strain IR‐1 had two‐fold higher chlorophyll and β‐carotene concentration than Gh‐U. IR‐1 had around four‐fold higher superoxide dismutase, ascorbate peroxidase and pyrogallol peroxidase activities than Gh‐U on a protein basis. Ascorbate and glutathione concentrations and redox state did not differ between strains and there was little difference in the activity of ascorbate–glutathione cycle enzymes (monodehydroascorbate reductase [E.C. 1.6.5.4], dehydroascorbate reductase [E.C. 1.8.5.1] and glutathione reductase [E.C. 1.8.1.7]). The response of these antioxidants to high light and low temperature was assessed by transferring cells from normal growth conditions (28°C, photon flux density of 100 μmol m^?2 s^?1)to 28°C/1200 μmol m^?2 s^?1; 13°C/100 μmol m^?2 s^?1; 13°C/1200 μmol m^?2 s^?1 and 28°C/100 μmol m^?2 s^?1 for 24 h. Low temperature and combined high light‐low temperature decreased chlorophyll and β‐carotene in both strains indicating that these treatments cause photooxidative stress. High light, low temperature and combined high light‐low temperature treatments increased the total ascorbate pool by 10–50% and the total glutathione pool by 20–100% with no consistent effect on their redox state. Activities of ascorbate–glutathione cycle enzymes were not greatly affected but all the treatments increased superoxide dismutase activity. It is concluded that D. salina can partially adjust to photooxidative conditions by increasing superoxide dismutase activity, ascorbate and glutathione.     

Astaxanthin diferulate as a bifunctional antioxidant

Abstract

Astaxanthin when esterified with ferulic acid is better singlet oxygen quencher with k₂ = (1.58 ± 0.1) 10¹⁰ L mol^{? 1}s^{? 1} in ethanol at 25°C compared with astaxanthin with k₂ = (1.12 ± 0.01) 10⁹ L mol^{? 1}s^{? 1}. The ferulate moiety in the astaxanthin diester is a better radical scavenger than free ferulic acid as seen from the rate constant of scavenging of 1-hydroxyethyl radicals in ethanol at 25°C with a second-order rate constant of (1.68 ± 0.1) 10⁸ L mol^{? 1}s^{? 1} compared with (1.60 ± 0.03) 10⁷ L mol^{? 1}s^{? 1} for the astaxanthin:ferulic acid mixture, 1:2 equivalents. The mutual enhancement of antioxidant activity for the newly synthetized astaxanthin diferulate becoming a bifunctional antioxidant is rationalized according to a two-dimensional classification plot for electron donation and electron acceptance capability.     

Characterization and comparisons of five N2-fixing Azolla-Anabaena associations,I. Optimization of growth conditions for biomass increase and N content in a controlled environment*

Abstract Biomass increase, C and N content, C₂H₂ reduction, percentage dry weight and chlorophyll a/b ratios were determined for clones of Azolla caroliniana Willd., A. filiculoides Lam., A. mexicana Presl., and A. pinnata R. Br. as a function of nutrient solution, pH, temperature, photoperiod, and light intensity in controlled environment studies. These studies were supplemented by a glasshouse study. Under a 16 h, 26°C day at a light intensity of 200 μmol m^?2 s^?1 and an 8 h, 19° C dark period, there was no significant difference in the growth rates of the individual species on the five nutrient solutions employed. Growth was comparable from pH 5 to pH 8, but decreased at pH 9. Using the same photoperiod and light intensity but constant growth temperatures of 15–40°C, at 5°C intervals, the individual species exhibited maximum growth, nitro-genase (N²ase) activity and N content at either 25° or 30°C. There was no difference in the temperature optima at pH 6 and pH 8. The tolerance of the individual species to elevated temperature was indicated to be A. mexicana> A. pinnata> A. caroliniana> A.filiculoides. At the optimum temperature, growth rates increased with increasing photoperiod at both pH 6 and pH 8 but N₂ase activity was usually highest at a 16 h light period. At photon flux densities of 100, 200, 400 and 600 μmol m^?2 s^?1, during a 16 h light period and optimum growth temperature of the individual species, N₂ase activity was saturated at less than 200 μmol m^?2 s^?1 and growth at 400 μmol m^?2 s^?1.No interacting effects of light and pH were noted for any species, nor were light intensities up to 1700 μmol m^?2 s^?1 detrimental to the growth rate or N content of any species in a 5 week glasshouse study with a natural 14.5 h light period and a constant temperature of 27.5°C. Using the optimum growth temperature, a 16 h light period, and a photon flux density of at least 400 μmol m^?2 s^?1, the Azolla species all doubled their biomass in 2 days or less and contained 5–6% N on a dry weight basis.     

TEMPERATURE EFFECTS ON SILICON LIMITED GROWTH OF THE LAKE MICHIGAN DIATOM STEPHANODISCUS MINUTUS (BACILLARIOPHYCEAE)1

The effect of temperature on the silicon limited growth and nutrient kinetics of Stephanodiscus minutus Grun. was examined using batch and semicontinuous culture methods. Short-term batch culture methods gave maximum growth rates which were essentially constant over the temperature range of 10° to 20°C (μ₃= 0.71–0.80 d^?1). The half-saturation constant for growth (K_s) was significantly lowest at 10°C (K_s= 0.31 μM Si; 0.22–0.41), and higher at both 15°C (K_s= 1.03 μM Si; 0.68–1.47) and 20°C (K_s= 0.88 μM Si; 0.60–1.22). Two methods were used to evaluate the semicontinuous experiments. The Droop relationship showed that the minimum cell quota was about 1.50 × 10^?7 nmol Si cell^?1, but there was much overlap in the results at all three temperatures. The Monod growth relationship for the semicontinuous experiments gave estimates of K_s which were lowest at 15°C (K_s= 0.12 μM Si), and higher at 10°C (K_s= 0.68 μM Si) and 20°C (K_s= 1.24 μM Si), although 95% confidence intervals overlapped. The maximum growth rate estimates for the semicontinuous experiments were similar at 10° and 15°, and higher at 20°C, but the number of points used in making the calculations makes the results less reliable than those from batch cultures. Generally, there were no consistent significant differences in the silicon limited growth of S. minutus over the temperature range studied. Our values of K_s for S. minutus are the lowest recorded for a freshwater diatom, and are consistent with the distribution of this species in nature. Generally, this species becomes abundant in areas with high phosphorus loading and very low silicon levels (low Si:P loading rates). Stephanodiscus species are also fossil indicators of eutrophication in north temperate lakes.     

SYMBIOSIS IN THE PLANKTONIC FORAMINIFER,ORBULINA UNIVERSA,AND THE ISOLATION OF ITS SYMBIOTIC DINOFLAGELLATE,GYMNODINIUM BÉII SP. NOV.1

The symbiotic association of the spinose planktonic foraminifer, Orbulina universa, with the dinoflagellate, Gymnodinium béii sp. nov., was examined with light and electron microscopy, and the symbiont was isolated into unialgal culture. The intact association is characterized by a diurnal movement of the symbionts from the distal regions of the spines during the day, to perialgal vacuoles within the host cytoplasm at night. This diurnal migration involves a daily endo- exocytotic cycle. Gymnodinium béii is non-motile and spindle-shaped within the host, whereas it is motile and gymnodinoid in shape when in culture. Ultrastructural examination revealed two or more stalked pyrenoids penetrated by lamellae, a typical dinokaryon nucleus and no trichocysts. A distinct ‘flange’projects over the sulcus from the hypocone. The swimming behavior of this dinoflagellate was characterized by intermittent darting events. Swimming speeds during a dart reached velocities of 770 μm. s^?1 as compared to a mean, non-darting swimming velocity of 126 μm. s^?1. Gymnodinium béii is eurythermal and division rates ranged between 0.16 and 0.65 divisions day^?1 for culture temperatures between 6.5 and 25° C respectively.     

COMPARISON OF DEVELOPMENT AND PHOTOSYNTHETIC GROWTH FOR FILAMENT CLUMPS AND REGENERATED MICROPLANTLET CULTURES OF AGARDHIELLA SUBULATA (RHODOPHYTA, GIGARTINALES)

Two axenic, in vitro liquid suspension cultures were established for Agardhiella subulata (C. Agardh) Kraft et Wynne, and their growth characteristics were compared. This study illustrated how reliable routes for the development of suspension cultures of macrophytic red algae of terete thallus morphology can be achieved for biotechnology applications. Undifferentiated filament clumps of 2–8 mm diameter were established by induction of callus-like tissue from thallus explants, and lightly branched microplantlets of 2–10 mm length were established by regeneration of filament clumps. The filament clumps were susceptible to regeneration. Adventitious shoot formation was reliably induced from 40% to 70% of the filament clumps by gentle mixing at 100 rev min^?1 on an orbital shaker. The specific growth rate of the microplantlets was higher than the filament clumps in nonagitated well plate culture (4%–6% per day for microplantlets vs. 2%–3% per day for filament clumps) at 24° C and 8–36 μmol photons·m^?2·s^?1 irradiance (10:14 h LD cycle) when grown on ASP12 artificial seawater medium at pH 8.6–8.9 with 20%–25% per day medium replacement. Oxygen evolution rate vs. irradiance measurements showed that relative to the filament clumps, microplantlets had a higher maximum specific oxygen evolution rate (P_o,max= 0.181 ± 0.035 vs. 0.130 ± 0.023 mmol O₂·g^?1 dry cell mass·h^?1), but comparable respiration rate (Q_o= 0.040 ± 0.013 vs. 0.033 ± 0.017 mmol O₂·g^?1 dry cell mass·h^?1), compensation point (I_c= 3.8 ± 2.4 vs. 5.7 ± 1.2 μmol photons·m^?2·s^?1), and light intensity at 63.2% of saturation (I_k= 17.5 ± 3.9 vs. 14.9 ± 2.6 μmol photons·m^?2·s^?1). The microplantlet culture was more suitable for suspension culture development than the filament clump culture because it was morphologically stable and exhibited higher growth rates.     

Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

Respiration of thermogenic inflorescences of skunk cabbage Symplocarpus renifolius in heliox

The respiration rate of the thermogenic inflorescences of Japanese skunk cabbage Symplocarpus renifolius can reach 300 nmol s^?1 g^?1, which is sufficient to raise spadix temperature (T_s) up to 15 ° C above ambient air temperature (T_a). Respiration rate is inversely related to T_a, such that the T_s achieves a degree of independence from T_a, an effect known as temperature regulation. Here, we measure oxygen consumption rate (?o ₂) in air (21% O₂ in mainly N₂) and in heliox (21% O₂ in He) to investigate the diffusive conductance of the network of gas‐filled spaces and the thermoregulatory response. When T_s was clamped at 15 ° C, the temperature that produces maximal ?o ₂ in this species, exposure to high diffusivity heliox increased mean ?o ₂ significantly from 137 ± 17 to 202 ± 43 nmol s^?1 g^?1 FW, indicating that respiration in air is normally limited by diffusion in the gas phase and some mitochondria are unsaturated. When T_a was clamped at 15 ° C and T_s was allowed to vary, exposure to heliox reduced T_s 1 ° C and increased ?o ₂ significantly from 116 ± 10 to 137 ± 19 nmol s^?1 g^?1, indicating that enhanced heat loss by conduction and convection can elicit the thermoregulatory response.     

Effect of irradiance and temperature on the photosynthesis of a cultivated red alga,Pyropia tenera (= Porphyra tenera), at the southern limit of distribution in Japan

The effect of irradiance and temperature on the photosynthesis of the red alga, Pyropia tenera, was determined for maricultured gametophytes and sporophytes collected from a region that is known as one of the southern limits of its distribution in Japan. Macroscopic gametophytes were examined using both pulse‐amplitude modulated fluorometry and/or dissolved oxygen sensors. A model of the net photosynthesis–irradiance (P‐E) relationship of the gametophytes at 12°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 46 μmol photons m^?2 s^?1, and the compensation irradiance was 9 μmol photons m^?2 s^?1. Gross photosynthesis and dark respiration for the gametophytes were also determined over a range of temperatures (8–34°C), revealing that the gross photosynthetic rates of 46.3 μmol O₂ mg_chl‐a^?1 min^?1 was highest at 9.3 (95% Bayesian credible interval (BCI): 2.3–14.5)°C, and the dark respiration rate increased at a rate of 0.93 μmol O₂ mg_chl‐a^?1 min^?1°C^?1. The measured dark respiration rates ranged from ?0.06 μmol O₂ mg_chl‐a^?1 min^?1 at 6°C to ?25.2 μmol O₂ mg_chl‐a^?1 min^?1 at 34°C. The highest value of the maximum quantum yield (Fv/Fm) for the gametophytes occurred at 22.4 (BCI: 21.5–23.3) °C and was 0.48 (BCI: 0.475–0.486), although those of the sporophyte occurred at 12.9 (BCI: 7.4–15.1) °C and was 0.52 (BCI: 0.506–0.544). This species may be considered well‐adapted to the current range of seawater temperatures in this region. However, since the gametophytes have such a low temperature requirement, they are most likely close to their tolerable temperatures in the natural environment.