Kinetics of conformational changes in tRNAPhe (yeast) as studied by the fluorescence of the y-base and of formycin substituted for the 3'-terminal adenine

The kinetics of the melting transitions of tRNA^phe (yeast) were followed by the fluorescence of the Y-base and of formycin substituted for the 3'-terminal adenine. As judged from differential UV absorbance melting cutves the formycin label had virtually no influence on the conformation of the tRNA. A temperature jump apparatus was modified to allow the simultaneous observation of transmission and fluorescence intensities by two independent optical channels. The design of a temperature jump cell with an all quartz center piece is given. The cell is resistant to temperatures up to 90°C; it provides high optical sensitivity, low stray light intensity and the possibility of measuring fluorescence polarization. The T-jump experiments allowed to discriminate between fast unspecific fluorescence quenching (τ <5 μsec) and slow co-operative conformational changes. In the central part of the temperature range of UV-melung (midpoint temperature 30°C in 0.01 M Na⁺ and 39°C in 0.03 M Na⁺, pH 6.8) two resolvable relaxation processes were observed. The coirssponding relaxation times were 20 msec and 800 msec at 30°C in 0.01 M Na⁺, and 4 msec and 120 msec at 39°C in 0.03 M Na⁺. The Y-base fluorescence shows both of the relaxation effects, which almost cancel in equilibrium fluorescence melting, because their amplitudes have opposite signs. From this finding the existence of some residual tertiary structure is inferred which persists after the unfolding of the main part of tertiary structure durirg early melting (midpoint temperature 24°C in 0.03 M Na⁺). In the fluorescence sigXXX of the formycin also the two relaxation effects appear. Both of them are connected with a decrease of the fluorescence intensity. From the results a coupled opening of the anticodon and acceptor branches is concluded.Enzymes: phenylalanyl-tRNA synthetase, PRS (EC 6.1.1.-20); ATP (CTP) tRNA nucleotidyl transferase, NT (EC 2.7.7.-20); alkaline phosphatase (EC 3-1-3.1).     

Acclimatization of K+ uptake to changes in root temperature: experiments with oilseed rape and barley in flowing solution culture

Abstract Changes in the net uptake rate of K⁺ and in the average tissue concentration of K⁺ were measured over 14 d in response to changes in root temperature with oilseed rape (Brassica napus L. cv. Bien venu) and barley (Hordeum vulgare L. cv. Atem). Plants were grown in flowing nutrient solutions containing 2.5 mmol m^?3 K⁺ and were acclimatized over 49 d (rape) or 28 d (barley) to low root temperature (5°C) prior to steady–state treatments at root temperatures between 3 °C and 25 °C, with common air temperature. Uptake of K⁺ was monitored continuously over 14 d and nitrogen was supplied as NH₄⁺+ NO^?₃ or NH⁺₄ or NO^?₃. Unit absorption rates of K⁺ increased with time and with root temperature up to Day 4 or 5 following the change in root temperature. Thereafter they usually approached steady-state, with Q₁₀? 2.0 between 7 °C and 17°C, although rates became similar between 7 °C and 13°C. Uptake of K⁺ by rape plants was invariably greater under NO^?₃ nutrition compared with NH⁺₄. The percentage K⁺ in the plant dry matter increased with temperature from 2% at 3 °C to 4% at 25 °C in rape, but there was less effect of temperature on the average concentrations of K⁺ in the plant fresh weight or plant water content. Concentrations of K⁺ in the leaf water fraction of rape plants decreased with increasing root temperature, but in barley they increased with increasing root temperature. Concentrations of K⁺ in the root water fraction were relatively stable with respect to root temperature. The results are discussed in terms of compensatory changes in K⁺ uptake following a change in root temperature and the relationships between growth, shoot: root ratio and K⁺ composition of the plant.     

DETERMINING THE ADULT AGE OF THE ORIENTAL LATRINE FLY, CHRYSOMYA MEGACEPHALA (FABRICIUS) (DIPTERA: CALLIPHORIDAE) BY PTERIDINE FLUORESCENCE ANALYSIS

The relationship between head pteridine fluorescence (HPF) levels and age in adult females and males of a common necrophagous fly, Chrysomya megacephala, and effects of temperature and fly sex on the relationship were studied by pteridine fluorescence spectrophotometry. Factors affecting HPF levels in flies were found to include fly age, temperature and fly sex, among which the fly age was the most dominant one. There were significant linear relationships between HPF levels and age both for female and male adult flies at five constant temperatures, i. e. 16°C, 20°C, 24°C, 28°C and 32°C. The relationship between mean rate of pteridine accumulation (FV or MV) and temperature (t) could be well described by a modified exponential equation of FV=0.01288 e^{(0.2241t‐3.127)}+0.3649 (r²= 0.9987) for females and a linear regression equation of MV= 0.0574 t ‐ 0.3637 (r²= 0.9557) for males. Using the information from the experiments at five constant temperatures, three calculated methods as the candidates were developed for accurately determining the age of the fly by HPF levels at ambient temperature. The results revealed that these three methods were suitable for estimating the age only for male flies, but not for female flies. The smallest average error of the predicated age was 2.55 days for males. In addition, how to employ which of these three developed methods for determining ages of male flies in practical was also discussed.     

EFFECTS OF LONG TERM EXPOSURE TO LOW TEMPERATURE ON THE PHOTOSYNTHETIC APPARATUS OF DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The effects of long term exposure to suboptimal growth temperature on the photosynthetic apparatus of Dunaliella tertiolecta Butcher were investigated using carbon fixation rate versus irradiance curves and the variable fluorescence induction method. Carbon fixation rates per unite chlorophyll a at saturating (p^B_m) and subsaturating (α^B) irradiances were 55% and 39% lower, respectively, at 12° C than at 20° C. Chlorophyll a quotas and the spectrally averaged in vivo absorption cross section normalized to chlorophyll a (a^*) were not significantly different at these two temperatures. Analysis of the fluorescence kinetics revealed 1) no significant variations of the amount of PSII photoactive reaction centers per unit chlorophyll a, 2) a 14% decrease of the PSII quantum yield(+) and 3) a 29% decrease of the energy transfer efficiency between the light harvesting chlorophyll a pigment bed and the PSII reaction centers. The decrease in energy transfer efficiency between the antennae and the PSII reaction centers at 12° C was interpreted as a mechanism to avoid photoinhibition.     

The effects of gill remodeling on transepithelial sodium fluxes and the distribution of presumptive sodium-transporting ionocytes in goldfish (Carassius auratus)

Goldfish, Carassius auratus, adaptively remodel their gills in response to changes in ambient oxygen and temperature, altering the functional lamellar surface area to balance the opposing requirements for respiration and osmoregulation. In this study, the effects of thermal- and hypoxia-mediated gill remodeling on branchial Na⁺ fluxes and the distribution of putative Na⁺-transporting ionocytes in goldfish were assessed. When assessed either in vitro (isolated gill arches) or in vivo at a common water temperature, the presence of an interlamellar cell mass (ILCM) in fish acclimated to 7°C clearly decreased Na⁺ efflux across the gill relative to fish maintained at 25°C and lacking an ILCM. However, loss of the ILCM in 7°C-acclimated fish exposed to hypoxia led to a decrease in Na⁺ efflux (assessed under hypoxic conditions) despite the apparent large increases in functional lamellar surface area. Goldfish possessing an ILCM were able to sustain Na⁺ uptake, albeit at a lower rate matched to efflux, owing to the re-distribution of ionocytes expressing genes thought to be involved in Na⁺ uptake [Na⁺/H⁺ exchanger isoform 3 (NHE3) and V- type H⁺-ATPase] to the edge of the ILCM where they can establish contact with the surrounding environment. NHE-expressing cells co-localized with Na⁺/K⁺-ATPase expression, suggesting a role for NHE in Na⁺-uptake in the goldfish. Implications of the ILCM on ion fluxes in the goldfish are discussed.     

OBSERVATIONS ON THE SURVIVAL AND GERMINATION OF RESTING SPORES OF THREE CHAETOCEROS (BACILLARIOPHYCEAE) SPECIES1,2

Resting spores (hypnospores) of Chaetoceros diadema (Ehrenberg) Gran, Chaetoceros vanheurckii Gran, and Chaetoceros didymus Ehrenberg were collected from a large plastic enclosure moored in Saanich Inlet, B.C., Canada. The effects of combinations of temperature and irradiance on the germination of these resting spores were investigated. Nutrient uptake, carbon fixation, and changes in the photosynthetic capacity of the germinating spores were also examined. Resting spores germinated optimally at combinations of temperature and irradiance similar to those in the environment during sporulation. They did not germinate at irradiances 1.3 μEin m^?2 s^?1 or temperatures >25.3° C. Nitrate, phosphate and silicate were taken up after the resting spores had germinated and resumed vegetative growth. Chlorophyll a fluorescence in vivo, and the DCMU-induced increase in in vivo fluorescence also increased after the resting spores had germinated. Resting spores began to fix carbon as soon as they were placed in light. Spores remained viable for at least 645 d. The length of time between first exposure to light and germination did not change during this period; however, the percentage of viable resting spores decreased markedly. None of the Chaetoceros spores germinated after 737 d of storage at 2–4° C in darkness.     

Effects of temperature on growth and metabolism in juvenile turbot

The effects of constant temperatures on growth, food efficiency, and physiological status were studied in four different batches of juvenile turbot. The growth responses were studied in three experiments lasting 70–85 days under 8–20° C thermal conditions. There was a positive correlation between growth and temperature from 8 to 17° C and a plateau was observed from 17 to 20° C. In fish fed to satiety, specific growth rate was positively correlated to the food intake, which was double at 20° C, compared with 8° C. Minor changes were observed in food efficiency. Body fat deposition decreased as temperature increased (25% lower at 20° C, compared with 8° C). Apparent food conversion, PER (protein efficiency ratio) and PUC (protein utilization coefficient) ranges were 0.8–0.9, 2.1–2.3 and 33–38% respectively. In 70–300 g fish, routine MO₂ increased (2.5–6.5 μmol O₂ h^?1 g bw^?1) with temperature up to 20° C, while larger turbot (500–600 g) appeared relatively thermo-independent, with a lower oxygen consumption (1.5 ìmol h^?1 g^?1). The average daily total ammonia nitrogen (TAN) and urea-N excretion per fish biomass was positively related to temperature. TAN was 30% lower at 8° C, compared with 20° C. Ingested nitrogen was mainly excreted under the final form of TAN, urea-N representing 26% of the total amount. A post-prandial peak in TAN and a delayed peak in urea-N nitrogen were observed. The hydromineral status [osmolarity, sodium, chloride and potassium blood plasma, gill (Na⁺-K⁺)-ATPase activity] of turbot was not affected by progressive changes in temperature during the acclimation period. Juvenile turbots show remarkable homeostatic capacities and so they have a relatively thermo-independent physiology within the range of temperature studied.     

Life history parameters for Nesidiocoris tenuis (Reuter) (Het., Miridae) under different temperature regimes

The development time for eggs and nymphs and female fertility were determined for Nesidiocoris tenuis Reuter (Het., Miridae: Dicyphini) at 15, 20, 25, 30, 35 and 40 ± 1°C, using tomato, Solanum esculentum (Miller), as substrate and eggs of Ephestia kuehniella Zeller as substitute prey. At 40°C, N. tenuis was unable to develop and barely reproduced. Egg development ranged from 30.8 days at 15°C to 6.3 days at 35°C. The cumulative thermal requirements for the eggs were 148.6 degree days (°d) and the lower thermal threshold, 10.3°C. The duration of the nymphal instar decreased from 55.9 days at 15°C to 8.6 days at 35°C. The thermal constant for the nymphs was 182.3 °d and the lower thermal threshold 11.7°C. No nymphs survived at 40°C, and the highest mortalities were at extreme temperatures (15 and 35°C). Female and male weights were influenced significantly by temperature. The fertility of N. tenuis females was reduced greatly at 15 and 40°C. The highest fertility during an observation period of 18 days following female emergence (79.5–60.0 nymphs per female) was within the temperature range of 20 to 35°C. Fertility was related directly to female weight and temperature (r² = 0.932). Based on development, reproduction data and thermal requirements, the optimum temperature range for N. tenuis was established as being between 20 and 30°C. Overall, N. tenuis is the most thermophilous of all dicyphines from vegetable crops in the Mediterranean area studied so far.     

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.     

A diffusional analysis of the temperature sensitivity of the Mg2+-induced rise of chlorophyll fluorescence from pea thylakoid membranes

The kinetics of the chlorophyll fluorescence rise induced by adding 20 mM MgCl₂ to a suspension of isolated pea chloroplasts treated with 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) have been examined experimentally and theoretically as a function of temperature. The application of similarity arguments and particle aggregation theory to the experimental results suggests that at the first approximation, the salt-induced time-dependent fluorescence changes may be described by the diffusion-controlled lateral movement of Photosystem II pigment-protein complexes. From an analysis of the temperature dependence of the fluorescence changes, estimates obtained for the lateral diffusion coefficients were 1.85 · 10^?12–3.08 · 10^?11 cm²/s over the temperature range 10°C ? T?30°C.     

Absorption of nitrate and ammonium ions by Lolium perenne from flowing solution cultures at low root temperatures

Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH₄ or NO3 at 10 mmol m^?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO₃. The specific absorption rate (SAR) of NH⁺₄ was greater at all temperatures than SAR-NO₃. In plants grown with NH⁺, 3–5% of the total N was recovered as NH⁺₄, whereas in those grown with NO^?₃ the unassimilated NO^?₃ rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH⁺₄ lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO^?₃-grown plants. Plants grown with NH⁺₄ had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO^?₃ grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH⁺₄ or NO^?₃. The additional residual N (protein) in NH⁺₄ grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient.     

In-situ determination of intracellular concentrations of K+ in barley (Hordeum vulgare L. cv. Kara) using the K+-binding fluorescent dye benzofuran isophthalate

The tetra[acetoxymethyl] ester of the K⁺-binding fluorescent dye benzofuran isophthalate (PBFI-AM) was used to determine changes in intracellular potassium (K⁺) concentrations and to measure net transport of K⁺ in barley (Hordeum vulgare L. cv. Kara) root and leaf protoplasts. When this dye binds to free K⁺ inside the cytoplasm, the fluorescence intensity ratio 340/380 nm increases in direct relation to the K⁺ concentration. Because of a delay in the uptake of dye into the vacuoles, it is possible to determine K⁺ concentrations in the vacuoles and transport of K⁺ from the cytoplasm into the vacuole. The uptake of PBFI-AM in root and leaf protoplasts of barley differed in the absence or presence of external K⁺ and was faster at pH 5.5 than at pH 7.0. The fluorescence intensity of the dye was stable for at least 20 h when the protoplasts were kept at 4°C. In the presence of nigericin, the fluorescence intensity of both cells and protoplasts was linearly related to the external concentration of K⁺ (up to 100 mM).     

AKINETE FORMATION IN PLANKTONIC ANABAENA SPP. (CYANOBACTEFUA) BY TREATMENT WITH LOW TEMPERATURE1

The effects of temperature, light intensity and nutrient depletion on akinete formation in seven strains of planktonic Anabaena spp.: A. mucosa TAC426; A. crassa TAC436; A. spiroides TAC443 and TAC444; A. flosaquae TAC446; and A. ucrainica TAC448 and TAC449 were examined. A Marked Pfft of temperature on akinete formation was observed at 40 μmol photons·m^?2·sec^?1 and nutrient-sufficient conditions. At 20° C, akinetes did not develop in A. mucosa TAC426, A. crassa TAC436, A. spiroides TAC443, A. flos-aquae TAC446, or A. ucrainica TAC449 but were formed at frequencies of a little over 11% (ratio of filaments with akinetes to total filaments) in A. spiroides TAC444 and A. ucrainica TAC448. None of the strains fmd akinetes or heterocysts at 30° C and 35° C. At lower temperature (10° C and 15° C), akinetes developed in all the strains at maximum frequencies of 13.4–77.4% during the late exponential phase or late exponential to stationary phases of growth. With only one exception, low light or nutrient deletion did not lead to the induction of akinete diferentiation at 20° C. Only akinete formation in A. flosaquae TAC446 was induced by nitrogen deletion with a frequency of 12.1%, similar to that induced by low temperature, but the initiation of akinete formation in the strain was delayed compared to treatment with low temperature. These results show that temperature was the most important environmental factor triggering akinete formation in these species. In A. crassa TAC436 and A. spiroides TAC443 and TAC444, akinetes developed during the late exponential growth phase even though heterocysts were formed at a 100% frequency (ratio of filaments with heterocysts to total filaments) throughout the entire growth phase. In A. mucosa TAC426, A. flos-aquae TAC446, and A. ucrainica TAC448 and TAC449, there was a positive correlation between heterocyst and akinete formation, suggesting that the presence of a heterocyst may play a role in akinete formation.     

Photosynthetic activity of a temperate coral Acropora pruinosa (Scleractinia, Anthozoa) with symbiotic algae in Japan

Physiological properties of the temperate hermatypic coral Acropora pruinosa Brook with symbiotic algae (zooxanthellae) on the southern coast of the Izu Peninsula, Shizuoka Prefecture, central Japan, were compared between summer and winter. Photosynthesis and respiration rates of the coral with symbiotic zooxanthellae were measured in summer and winter under controlled temperatures and irradiances with a differential gasvolumeter (Productmeter). Net photosynthetic rate under all irradiances was higher in winter than in summer at the lower range of temperature (12–20°C), while lower than in summer at the higher range of temperature (20–30°C). The optimum temperature for net photosynthesis was apt to fall with the decrease of irradiance both in summer and winter, whereas it was higher in summer than in winter under each irradiance. At 25/ 50/100 μmol photons nr² s^?1, it was nearly the sea‐water temperature in each season. Dark respiration rate was higher in winter than in summer, especially in the range from 20–30°C. In both seasons the optimum temperature for gross photosynthesis was 28°C under 400 μmol photons nr² s^?1 and lowered with decreasing irradiance up to 22°C under 25 μmol photons nr² s^?1 in summer, while 20°C under the same irradiance in winter. The optimum temperature for production/respiration (P/R) ratio was higher in summer than in winter under each irradiance. Results indicated that metabolism of coral and zooxanthellae is adapted to ambient temperature condition under nearly natural irradiance in each season.     

The kinetics of light-induced changes of C-550, cytochrome b559 and fluorescence yield in chloroplasts at low temperature

The kinetics of the photoreduction of C-550, the photooxidation of cytochrome b₅₅₉ and the fluorescence yield changes during irradiation of chloroplasts at ?196 °C were measured and compared. The photoreduction of C-550 proceeded more rapidly than the photooxidation of cytochrome b₅₅₉ and the fluorescence yield increase followed the cytochrome b₅₅₉ oxidation. These results suggest that fluorescence yield under these conditions indicates the dark reduction of the primary electron donor to Photosystem II, P680⁺, by cytochrome b₅₅₉ rather than the photoreduction of the primary electron acceptor.The photoreduction of C-550 showed little if any temperature dependence over the range of ?196 to ?100 °C. The amount of cytochrome b₅₅₉ photooxidized was sensitive to temperature decreasing from the maximal change at temperatures between ?196 to ?160 °C to no change at ?100 °C. To the extent that the reaction occurred at temperatures between ?160 and ?100 °C the rate was largely independent of temperature. The rate of the fluorescence increase was dependent on temperature over this range being 3–4 times more rapid at ?100 than at ?160 °C. At ?100 °C the light-induced fluorescence increase and the photoreduction of C-550 show similar kinetics. The temperature dependence of the fluorescence induction curve is attributed to the temperature dependence of the dark reduction of P680⁺.The intensity dependence of the photoreduction of C-550 and of the photooxidation of cytochrome b₅₅₉ are linear at low intensities (below 200 μW/cm²) but fall off at higher intensities. The failure of reciprocity in the photoreduction of C-550 at the higher intensities is not explained by the simple model proposed for the Photosystem II reaction centers.     

COMPARATIVE STUDY ON THE PHOTOSYNTHETIC PROPERTIES OF PRASIOLA (CHLOROPHYCEAE) AND NOSTOC (CYANOPHYCEAE) FROM ANTARCTIC AND NON‐ANTARCTIC SITES1

The terrestrial cyanobacterium Nostoc commune Vaucher ex Bornet et Flahault occurs worldwide, including in Japan and on the Antarctic continent. The terrestrial green alga Prasiola crispa (Lightf.) Kütz. is also distributed in Antarctica. These two species need to acclimate to the severe Antarctic climate including low ambient temperature and desiccation under strong light conditions. To clarify this acclimation process, the physiological characteristics of the photosynthetic systems of these two Antarctic terrestrial organisms were assessed. The relative rate of photosynthetic electron flow in N. commune collected in Japan and in Antarctica reached maxima at 900 and 1,100 μmol photons · m^?2 · s^?1, respectively. The difference seemed to reflect the presence of high amounts of UV‐absorbing substances within the Antarctic cyanobacterium. On the other hand, the optimal temperatures for photosynthesis at the two locations were 30°C–35°C and 20°C–25°C, respectively. This finding suggested a decreased photosynthetic thermotolerance in the Antarctic strain. P. crispa exhibited desiccation tolerance and dehydration‐induced quenching of PSII fluorescence. Re‐reduction of the photooxidized PSI reaction center, P700, was also inhibited at fully dry states. Photosynthetic electron flow in P. crispa reached a maximum at 20°C–25°C and at a light intensity of 700 μmol photons ? m^?2 ? s^?1. Interestingly, the osmolarity of P. crispa cells suggested that photosynthesis is performed using water absorbed in a liquid form rather than water absorbed from the air. Overall, these data suggest that these two species have acclimated to optimally photosynthesize under conditions of the highest light intensity and the highest temperature for their habitat in Antarctica.     

Environmental Optima for Seven Strains of Pseudochattonella (Dictyochophyceae,Heterokonta)

The ichthyotoxic flagellate Pseudochattonella has formed recurrent blooms in the North Sea, Skagerrak and Kattegat since 1998. Five strains of Pseudochattonella farcimen and two strains of P. verruculosa were examined in an assay comparing the light response of specific growth rates over a range of temperatures and salinities to get further knowledge on the autecology of members of this genus. Temperature optima were lower in P. farcimen (9°C–15°C) than in P. verruculosa (12°C–20°C). P. farcimen also showed a somewhat lower salinity optimum (18–26) than P. verruculosa (20–32). All strains showed light‐dependent growth responses reaching saturation between 18 and 52 μmol · photons · m^?2 · s^?1 at optimal temperature and salinity conditions. Compensation point estimates ranged from 4.2 to 15 μmol · photons · m^?2 · s^?1. Loss rates increased with temperature and were lowest at salinities close to optimal growth conditions. Blooms of P. farcimen have been recorded in nature under conditions more similar to those minimizing loss rates rather than those maximizing growth rates in our culture study.     

RESPONSE TO SALINITY AND HEAT STRESS IN TWO HALOTOLERANT CHLOROPHYTE ALGAE1

Two new isolates of halotolerant chlorophyte algae from the Salt Plains National Wildlife Refuge in Oklahoma, USA, tentatively identified as Dunaliella sp. Teodoresco and Nannochloris sp. Naumann, were characterized with respect to interaction between growth salinity and short‐term heat tolerance. Cells were cultured at 23–25° C over a wide range of salinity. In both species, salinity alone had little effect on maximum photochemical yield (measured by pulse modulated fluorescence) and integrity of the light harvesting system (77 K fluorescence emission spectra). In contrast, Nannochloris exhibited decreasing growth rate (μ), light‐saturated photosynthetic capacity (P^cell_max), respiration (R_d), light‐harvesting efficiency (α^cell), and chl content with increasing salinity. Cultures were heated for 2 h near their upper temperature limits (41.5° C for Dunaliella and 45° C for Nannochloris grown at 50 psu). Dunaliella was progressively more heat‐tolerant with increasing salinity. Photochemical yield of cells at 100 and 50 psu was inhibited by about 15% and 40%, respectively, and largely recovered within 30 min after return to 23° C. Thermal inhibition of photochemical yield in Nannochloris was about 45% at both 50 and 100 psu, but recovery was slower at 100 psu. At 20 psu, both species were almost 90% inhibited by high temperature and required more than a day to recover. In both species, 2 h of heating increased the PSI:PSII fluorescence emission ratio (714:690 nm) at all salinities. This ratio largely recovered within 24 h in Dunaliella at 50 and 100 psu and partially recovered in Nannochloris at 100 psu, but cells of both species heated at 20 psu were chlorotic the next day.     

Acclimation of potassium influx in rye (Secale cereale) to low root temperatures

The influx of K⁺(⁸⁶Rb⁺) into intact roots of rye (Secale cereale L. cv. Rheidal) exposed to a differential temperature (DT) between the root (8° C) and shoot (20° C) is initially reduced compared with warm-grown (WG) controls with both shoot and root maintained at 20° C. Over a period of 3 d, however, K⁺-influx rates into DT plants are restored to levels similar to or greater than those of the WG controls, the absolute rates of K⁺ influx being strongly dependent upon the shoot/root ratio. Acclimation in DT plants results in a reduction of K⁺ influx into the apical (0–2 cm) region of the seminal root which is associated with a compensatory increase in K⁺ influx into the more mature, basal regions of the root. Values of V _max and apparent K _m for K⁺ influx into DT plants were similar to those for WG plants at assay temperatures of 8° C and 20° C except for an increase in the apparent K _m at 8° C. The influx of K⁺ from solutions containing 0.6 mol·m^-3 K⁺ into both WG and DT plants was found to be linearly related to assay temperature over the range 2–27° C, and the temperature sensitivity of K⁺ influx to be dependent upon shoot/root ratio. At high shoot/root ratios, the ratio of K⁺ influx at 20° C:K⁺ influx at 8° C for WG plants approached a minimum value of 1.9 whereas that for DT plants approached unity indicating that K⁺ influx into DT plants has a large temperature-insensitive component. Additionally, when plants were grown in solutions of low potassium concentration, K⁺ influx into DT plants was consistently greater than that into WG plants, in spite of having a greater root potassium concentration ([K⁺]int). This result indicates some change in the regulation of K⁺ influx by [K⁺]int in plants exposed to low root temperatures. We suggest that K⁺ influx into rye seedlings exposed to low root temperatures is regulated by the increased demand placed on the root system by a proportionally larger shoot and that the acclimation of K⁺ influx to low temperatures may be the result of an increased hydraulic conductivity of the root system.Abbreviations DT differential temperature pretreatment - [K⁺]int root potassium concentration - [K⁺]ext potassium concentration of nutrient medium - WG warm-grown pretreatment     

LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA,CNIDARIA)1

Symbiodinium californium (#383, Banaszak et al. 1993 ) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5°C–30°C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15°C and 28°C (μ 0.21–0.26 · d^?1) and extremely low at 5, 10, and 30°C (0.02–0.03 · d^?1). Average doubling times ranged from 2.7 d (20°C) to 33 d (5, 10, and 30°C). Cells cultured at 10°C had the greatest cell volume (821 μm³) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light‐saturated maximum photosynthesis (P_max) increased from 2.9 pg C · cell^?1 · h^?1 at 20°C to 13.2 pg C · cell^?1 · h^?1 at 30°C, a 4.5‐fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30°C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.