Respective Growth Temperatures Research Articles

Two dimensional boron nitride growth on nickel foils by plasma assisted molecular beam epitaxy from elemental B and N sources

The growth of two dimensional sp2-bonded boron nitride (2D-BN) was studied in a plasma-assisted molecular beam epitaxy set-up, using independent boron and nitrogen sources. We studied the growth conditions on polycrystalline Ni foils: B and N respective fluxes, growth temperature and time, which are influencing the surface morphology, stoichiometry and the 2D-BN domain size. Using a B/N precursor flux ratio ≫1 yields films with incorporated boron largely in excess and intermixed with 2D-BN. On the contrary, precursor flux ratios from moderately B-rich to moderately N-rich leads to stoichiometric 2D-BN. The optimum growth temperature is found to be 900 °C, a temperature for which the crystallographic quality is improved compared to lower temperatures thanks to the increased adatom surface mobility although a partial sublimation of BN occurs. Increasing the growth time under the optimized settings shows that the growth does not occur in a layer-by-layer mode, but rather by stacking BN domains on top of each other with a rather slow lateral extension of the domains.

Impact of preculture temperature on peracetic acid-induced inactivation and sublethal injury of L. monocytogenes and subsequent growth potential of single cells

The disinfectant peracetic acid (PAA) that is used in the food industry can cause sublethal injury in L. monocytogenes. The effect of preculture temperature on the inactivation and sublethal injury of L. monocytogenes cells due to PAA was evaluated by plating on non-selective and selective agar medium supplemented with 5 % (w/v) NaCl. L. monocytogenes cells were precultured at 30 °C, 20 °C or 4 °C, and the former was used as reference temperature. Preculture of cells at 20 °C or 4 °C and subsequent exposure to PAA at the respective growth temperatures caused higher injury compared to cells grown at 30 °C and exposed to PAA 20 °C and PAA 4 °C, respectively. Survival was also affected by the preculture temperature; 20 °C-grown cultures resulted in lower survival at PAA 20 °C. Nevertheless, preculture at 4 °C resulted in a similar number of surviving cells when exposed to PAA 4 °C compared to cells precultured at 30 °C and exposed to PAA at 4 °C. Flow cytometry was subsequently used to quantify outgrowth capacity of stressed and sublethal damaged populations following sorting of single cells in nutrient rich medium (Tryptone soy broth supplemented with yeast extract [TSBY]). PAA treatment affected the outgrowth of L. monocytogenes at single-cell level resulting in increased outgrowth-times reflecting higher single cell heterogeneity. To conclude, the response of L. monocytogenes when exposed to PAA depended on the preculture conditions, and the highly heterogeneous outgrowth potential of PAA-injured cells may affect their detection accuracy and pose a food safety risk.

Acclimation of Ecophysiological and Agronomic Traits to Increasing Growth Temperature in Three Cowpea Genotypes Grown in Anuradhapura, Sri Lanka

The future of food crop production is uncertain due to the negative effects of global warming. Cowpea is grown in warm environments including in Sri Lanka, where less is known about the potential acclimation of ecophysiological and agronomic traits to increasing temperatures. We evaluated the acclimation potential of yield components and ecophysiological traits of three recommended cowpea genotypes to the seasonal variation in growth temperature in Anuradhapura, Sri Lanka. This study was conducted at the Faculty of Agriculture, Rajarata University of Sri Lanka, in two consecutive seasons with average daytime temperatures of 30.4°C and 33.2°C. Three genotypes, Dhawala, Waruni, and MI-35, were tested in this study, and their rates of leaf photosynthesis and respiration at the 50% flowering stage and final yield parameters were measured at their respective average growth temperatures in both seasons. The total yield per hectare showed an average decrease of 16%, 17%, and 22% in the Dhawala, Waruni, and MI-35 genotypes at high average growth temperature, respectively. These reductions were associated with the reduction in the number of seeds per pod, hundred seed weight, and number of pods per plant, suggesting that there could be an among-genotype variation in flower abscission, fertilization, and biomass partitioning during the season in which the average growth temperature was high. In the season with high average growth temperature, genotype Dhawala showed an increased carbon gain per unit carbon loss and increased water use efficiency compared to MI-35 and Waruni genotypes. Therefore, genotype Dhawala is a better candidate than MI-35 and Waruni genotypes in the face of global warming, which may be considered in further breeding programs and market preferences. More work is proposed to examine the patterns of biomass partitioning and radiation use efficiency in three cowpea genotypes at elevated temperatures.

Exploring the Metabolomic Responses of Bacillus licheniformis to Temperature Stress by Gas Chromatography/Mass Spectrometry.

Owing to its high protein secretion capacity, simple nutritional requirements, and GRAS (generally regarded as safe) status, Bacillus licheniformis is widely used as a host for the industrial production of enzymes, antibiotics, and peptides. However, as compared with its close relative Bacillus subtilis, little is known about the physiology and stress responses of B. licheniformis. To explore its temperature-stress metabolome, B. licheniformis strains ATCC 14580 and B186, with respective optimal growth temperatures of 42°C and 50°C, were cultured at 42°C, 50°C, and 60°C and their corresponding metabolic profiles were determined by gas chromatography/mass spectrometry and multivariate statistical analyses. It was found that with increased growth temperatures, the two B. licheniformis strains displayed elevated cellular levels of proline, glutamate, lysine, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, and octadecanoic acid, and decreased levels of glutamine and octadecenoic acid. Regulation of amino acid and fatty acid metabolism is likely to be associated with the evolution of protective biochemical mechanisms of B. licheniformis. Our results will help to optimize the industrial use of B. licheniformis and other important Bacillus species.

Homeostasis of the temperature sensitivity of respiration over a range of growth temperatures indicated by a modified Arrhenius model.

The temperature dependence of plant respiratory rate (R) changes in response to growth temperature. Here, we used a modified Arrhenius model incorporating the temperature dependence of activation energy (Eo ), and compared the temperature dependence of R between cold-sensitive and cold-tolerant species. We analyzed the temperature dependences of leaf CO2 efflux rate of plants cultivated at low (LT) or high temperature (HT). In plants grown at HT (HT plants), Eo at low measurement temperature varied among species, but Eo at growth temperature in HT plants did not vary and was comparable to that in plants grown at LT (LT plants), suggesting that the limiting process was similar at the respective growth temperatures. In LT plants, the integrated value of loge R, a measure of respiratory capacity, in cold-sensitive species was lower than that in cold-tolerant species. When plants were transferred from HT to LT, the respiratory capacity changed promptly after the transfer compared with the other parameters. These results suggest that a similar process limits R at different growth temperatures, and that the lower capacity of the respiratory system in cold-sensitive species may explain their low growth rate at LT.

Studies on Magnetic, Transport and Dielectric Properties of Ni0.65Zn0.35Fe2O4 Thin Films Grown by Pulsed Laser Deposition

The ferrimagnetic material Ni1-xZnxFe2O4 (NZFO) has drawn tremendous attention in recent years due to its potential applications in radio frequency coils, transformer cores, rod antennas, magnetic cores of read write heads for high-speed digital tape or disk recording and microwave devices owing to its remarkable magnetic properties, high resistivity and low eddy current. Other than these the NZFO is also considered as potential candidate for multiferroic composite structures. We have chosen Ni0.65Zn0.35Fe2O4 for the present investigation as this composition exhibits the highest saturation magnetization in the entire Ni–Zn family along with high magnetic curie temperature which is ~ 575 K. NZFO thin films were grown by pulsed laser deposition (PLD) at different substrate temperatures in the range of 500-800oC using a KrF excimer laser (λ=248 nm) on LaNiO3 buffered (001) oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates under oxygen pressure of 150 mTorr. These films were subsequently annealed at their respective growth temperature for 30 min in oxygen ambient at a partial pressure of ~ 300 Torr. The highly c-axis oriented growth containing only (004) diffraction peak of NZFO films along with in-plane epitaxial relationship was confirmed by high resolution X-ray diffraction measurements.From the atomic force micrographs it was observed that all the films were densely packed, smooth, free from microcrack and particulates with uniform grain-size distributions. X-ray Photoelectron Spectroscopy measurements confirmed that in all films the Ni, Zn and Fe elements retain their same oxidation states as in bulk target irrespective of growth temperature. The saturation magnetization (Ms ) of NZFO film was found to enhance systematically with increasing growth temperature. The resistance of NZFO films was found to decrease with increasing temperature indicating insulating behaviour. These films showed positive magneto resistance at low magnetic fields. Detailed dielectric, magnetic, magneto resistance and transport characterizations are currently underway and results will be discussed at the meeting.

The photosynthetic and respiratory responses to temperature and nitrogen supply in the marine green macroalga Ulva conglobata (Chlorophyta)

:Temperature effects on photosynthesis and respiration were investigated in the green macroalga, Ulva conglobata, collected from low rocky coast of Nanao Island, Shantou, China. Thalli were cultured at 15 and 25°C and at low nitrogen (LN) and high nitrogen (HN) availability. Dark respiration and light-saturating photosynthesis were measured as oxygen exchange; the characteristics of chlorophyll fluorescence were also assayed. The maximal photochemical yield (Fv/Fm) and maximum relative electron transport rates (rETRmax) remained stable with moderate fluctuations of temperature (15–30°C) in the short term. However, the values of Fv/Fm and rETRmax declined with the high temperature (≥ 35°C), and such a decline was more accentuated in 15°C- than 25°C-grown algae. Both the rates of photosynthesis and respiration were sensitive to measurement temperature, with the Q10 values being higher in 25°C-grown algae (HN) than 15°C-grown algae. It appeared that 25°C-grown algae displayed an optimum temperature (Topt) of 30°C for photosynthesis, while 15°C-grown algae exhibited the Topt of a range of 20–30°C. When measured at their respective growth temperature, the rates of photosynthesis were significant higher in 25°C- than 15°C-grown algae, while the rates of respiration were identical between 25°C- and 15°C-grown algae. Our results demonstrated that respiration displayed full acclimation; whereas, photosynthesis exhibited partial acclimation to changing growth temperatures in U. conglobata. Consequently, the balance between respiration and gross photosynthesis was re-established by changing growth temperature, with the ratio being lowered with warmer growth temperature. The results also showed that HN availability in culture significantly increased pigments and soluble protein contents and enhanced photosynthesis and respiration. We suggested that the acclimation potential of metabolisms in U. conglobata favored carbon acquisition and net carbon balance with the increasing seawater temperature resulting from climate change and/or increasing N loading from coastal eutrophication.

Do Homologous Thermophilic–Mesophilic Proteins Exhibit Similar Structures and Dynamics at Optimal Growth Temperatures? A Molecular Dynamics Simulation Study

Structure and dynamics both are known to be important for the activity of a protein. A fundamental question is whether a thermophilic protein and its mesophilic homologue exhibit similar dynamics at their respective optimal growth temperatures. We have addressed this question by performing molecular dynamics (MD) simulations of a natural mesophilic-thermophilic homologue pair at their respective optimal growth temperatures to compare their structural, dynamical, and solvent properties. The MD simulations were done in explicit aqueous solvent under periodic boundary and constant pressure and temperature (CPT) conditions and continued for 10.0 ns using the same protocol for the two proteins, excepting the temperatures. The trajectories were analyzed to compare the properties of the two proteins. Results indicated that the dynamical behaviors of the two proteins at the respective optimal growth temperatures were remarkably similar. For the common residues in the thermophilic protein, the rms fluctuations have a general trend to be slightly higher compared to that in the mesophilic counterpart. Lindemann parameter values indicated that only a few residues exhibited solid-like dynamics while the protein as a whole appeared as a molten globule in each case. Interestingly, the water-water interaction was found to be strikingly similar in spite of the difference in temperatures while, the protein-water interaction was significantly different in the two simulations.

Growth and photosynthesis in seedlings of Hizikia fusiformis (Harvey) Okamura (Sargassaceae, Phaeophyta) cultured at two different temperatures

This study examined temperature acclimation, growth, and photosynthetic characteristics of the zygote-derived seedlings of Hizikia fusiformis (Harvey) Okamura (Sargassaceae). The seedlings were cultured at 15°C or 25°C for 4 weeks. The average relative growth rate was significantly higher in seedlings acclimated at 25°C. The photosynthetic rate measured at 15°C was much higher in seedlings grown at 15°C than those grown at 25°C, indicating photosynthetic acclimation to a lower temperature. At 35°C, the photosynthetic rate of 15°C-grown seedlings was drastically decreased, whereas that of 25°C-grown seedlings was significantly increased. The maximum relative electron transport rate (rETRmax) measured at the respective growth temperature was significantly higher in seedlings grown at 25°C than at 15°C. At a measuring temperature of 35°C, the rETRmax in both 15°C- and 25°C-grown seedlings were considerably reduced with regard to those measured at 15°C or 25°C. Our results suggested that, compared with the seedlings grown at 25°C, those acclimated at a lower temperature could be disadvantaged under adverse conditions such as increased temperatures.

Cold-Tolerant Crop Species Have Greater Temperature Homeostasis of Leaf Respiration and Photosynthesis Than Cold-Sensitive Species

Some plant species show constant rates of respiration and photosynthesis measured at their respective growth temperatures (temperature homeostasis), whereas others do not. However, it is unclear what species show such temperature homeostasis and what factors affect the temperature homeostasis. To analyze the inherent ability of plants to acclimate respiration and photosynthesis to different growth temperatures, we examined 11 herbace-ous crops with different cold tolerance. Leaf respiration (R(area)) and photosynthetic rate (P(area)) under high light at 360 microl l(-1) CO(2) concentrations were measured in plants grown at 15 and 30 degrees C. Cold-tolerant species showed a greater extent of temperature homeostasis of both R(area) and P(area) than cold-sensitive species. The underlying mechanisms which caused differences in the extent of temperature homeostasis were examined. The extent of temperature homeostasis of P(area) was not determined by differences in leaf mass and nitrogen content per leaf area, but by differences in photosynthetic nitrogen use efficiency (PNUE). Moreover, differences in PNUE were due to differences in the maximum catalytic rate of Rubisco, Rubisco contents and amounts of nitrogen invested in Rubisco. These findings indicated that the temperature homeostasis of photosynthesis was regulated by various parameters. On the other hand, the extent of temperature homeostasis of R(area) was unrelated to the maximum activity of the respiratory enzyme (NAD-malic enzyme). The R(area)/P(area) ratio was maintained irrespective of the growth temperatures in all the species, suggesting that the extent of temperature homeostasis of R(area) interacted with the photosynthetic rate and/or the homeostasis of photosynthesis.

Photosynthetic response of wheat cultivar to long-term exposure to elevated temperature

Wheat (Triticum aestivum L. cv. HD 2285) was grown in control (C) and heated (H) open top chambers (OTCs) for entire period of growth and development till maturity. The mean maximum temperature of the entire period was 3 °C higher in H-compared to C-OTCs. Net photosynthetic rate (PN) measured at different temperature (20–40 °C) of C-and H-grown plants showed greater sensitivity to high temperature in H-plants. PN measured at respective growth temperature was lower in H-compared to C-plants. The CO2 and irradiance response curves of photosynthesis also showed lesser response in H-compared to C-plants. The initial slope of PNversus internal CO2 concentration (PN/Ci) curve was lower in H-than C-plants indicating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) limitation. In irradiance response curve, the plateau was lower in H-compared to C-plants which is interpreted as RuBPCO limitation. RuBPCO content in the leaves of C-and H-plants, however, was not significantly different. Ribulose-1,5-bisphosphate carboxylase (RuBPC) initial activity was lower in H-plants, whereas activity of fully activated enzyme was not affected, indicating a decrease in activation state of the enzyme. This was further substantiated by the observed decrease in RuBPCO activase activity in H-compared to C-plants. RuBPCO activase was thus sensitive even to moderate heat stress. The decrease in PN under moderate heat stress was mainly due to a decrease in activation state of RuBPCO catalysed by RuBPCO activase.

Thermal acclimation of photosynthesis in black spruce [Picea mariana (Mill.) B.S.P.

We investigated the thermal acclimation of photosynthesis and respiration in black spruce seedlings [Picea mariana (Mill.) B.S.P.] grown at 22/14 degrees C [low temperature (LT)] or 30/22 degrees C [high temperature (HT)] day/night temperatures. Net CO(2) assimilation rates (A(net)) were greater in LT than in HT seedlings below 30 degrees C, but were greater in HT seedlings above 30 degrees C. Dark and day respiration rates were similar between treatments at the respective growth temperatures. When respiration was factored out of the photosynthesis response to temperature, the resulting gross CO(2) assimilation rates (A(gross)) was lower in HT than in LT seedlings below 30 degrees C, but was similar above 30 degrees C. The reduced A(gross) of HT seedlings was associated with lower needle nitrogen content, lower ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) maximum carboxylation rates (V(cmax)) and lower maximum electron transport rates (J(max)). Growth treatment did not affect V(cmax) : J(max). Modelling of the CO(2) response of photosynthesis indicated that LT seedlings at 40 degrees C might have been limited by heat lability of Rubisco activase, but that in HT seedlings, Rubisco capacity was limiting. In sum, thermal acclimation of A(net) was largely caused by reduced respiration and lower nitrogen investments in needles from HT seedlings. At 40 degrees C, photosynthesis in LT seedlings might be limited by Rubisco activase capacity, while in HT seedlings, acclimation removed this limitation.

Challenge Testing the Lactoperoxidase System Against a Range of Bacteria Using Different Activation Agents

Lactoperoxidase (LP) exerts antimicrobial effects in combination with H2O2 and either thiocyanate (SCN−) or a halide (e.g., I−). Garlic extract in the presence of ethanol has also been used to activate the LP system. This study aimed to determine the effects of 3 LP activation systems (LP+SCN−+H2O2; LP+I−+H2O2; LP + garlic extract + ethanol) on the growth and activity of 3 test organisms (Staphylococcus aureus, Pseudomonas aeru-ginosa, and Bacillus cereus). Sterilized milk was used as the reaction medium, and the growth pattern of the organisms and a range of keeping quality (KQ) indicators (pH, titratable acidity, ethanol stability, clot on boiling) were monitored during storage at the respective optimum growth temperature for each organism. The LP+I−+ H2O2 system reduced bacterial counts below the detection limit shortly after treatment for all 3 organisms, and no bacteria could be detected for the duration of the experiment (35 to 55h). The KQ data confirmed that the milk remained unspoiled at the end of the experiments. The LP + garlic extract + ethanol system, on the other hand, had no effect on the growth or KQ with P. aeruginosa, but showed a small retardation of growth of the other 2 organisms, accompanied by small increases (5 to 10h) in KQ. The effects of the LP+SCN−+H2O2 system were intermediate between those of the other 2 systems and differed between organisms. With P. aeruginosa, the system exerted total inhibition within 10h of incubation, but the bacteria regained viability after a further 5h, following a logarithmic growth curve. This was reflected in the KQ indicators, which implied an extension of 15h. With the other 2 bacterial species, LP+SCN−+H2O2 exerted an obvious inhibitory effect, giving a lag phase in the growth curve of 5 to 10h and KQ extension of 10 to 15h. When used in combination, I− and SCN− displayed negative synergy.

A comparison of proline, thiol levels and GAPDH activity in cyanobacteria of different origins facing temperature-stress

Three cyanobacterial strains originating from different habitats were subjected to temperature shift exposures and monitored for levels of proline, thiol and activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Thermophile Mastigocladus laminosus (growth optimum, 40 °C), raised the proline level 4.2-fold at low temperature (20 °C), for the psychrophile Nostoc 593 (growth optimum, 20 °C), it was raised 8-fold at 40 °C while in the mesophile Nostoc muscorum (growth optimum, 30 °C), the imino acid level increased 2.3-fold during temperature ‘shiftdown’ to 20 °C or 3.5-fold in sets facing ‘shiftup’ (40 °C). Alterations in thiol levels in the above strains were in line with proline. It is suggested that such fluctuations reflect metabolic shifts as a response to stress. Interestingly, GAPDH activity was maximum at the respective growth temperature optimum of M. laminosus (122 nmol NADPH oxidized min −1 mg −1 protein) and Nostoc 593 (141 nmol NADPH oxidized min −1 mg −1 protein) while in N. muscorum, it increased at 40 °C (101 nmol NADPH oxidized min −1 mg −1 protein) and to 93.3 nmol NADPH oxidized min −1 mg −1 protein (20 °C) relative to 86 nmol NADPH oxidized min −1 mg −1 protein at 30 °C. It seems that extremophiles maintain the GAPDH activity/level during growth at their respective temperatures optimal while the mesophile increases it in order to cope up with temperature-stress.

Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings

The present study investigated whether the cold-sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35 ° C), mitochondrial membranes were characterized by a higher phosphatidylcholine : phosphatidylethanolamine ratio and a lower content in 18 : 3 fatty acid. After a reduction of temperature (from 25 to 18 ° ° ° C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35 ° C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18 ° C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35 ° C, but not at 18 ° C despite changes in lipid composition, in accordance with the cold-sensitive character of the plant.

The cell membrane plays a crucial role in survival of bacteria and archaea in extreme environments.

The cytoplasmic membrane of bacteria and archaea determine to a large extent the composition of the cytoplasm. Since the ion and in particular the proton and/or the sodium ion electrochemical gradients across the membranes are crucial for the bioenergetic conditions of these microorganisms, strategies are needed to restrict the permeation of these ions across their cytoplasmic membrane. The proton and sodium permeabilities of all biological membranes increase with the temperature. Psychrophilic and mesophilic bacteria, and mesophilic, (hyper)thermophilic and halophilic archaea are capable of adjusting the lipid composition of their membranes in such a way that the proton permeability at the respective growth temperature remains low and constant (homeo-proton permeability). Thermophilic bacteria, however, have more difficulties to restrict the proton permeation across their membrane at high temperatures and these organisms have to rely on the less permeable sodium ions for maintaining a high sodium-motive force for driving their energy requiring membrane-bound processes. Transport of solutes across the bacterial and archaeal membrane is mainly catalyzed by primary ATP driven transport systems or by proton or sodium motive force driven secondary transport systems. Unlike most bacteria, hyperthermophilic bacteria and archaea prefer primary ATP-driven uptake systems for their carbon and energy sources. Several high-affinity ABC transporters for sugars from hyperthermophiles have been identified and characterized. The activities of these ABC transporters allow these organisms to thrive in their nutrient-poor environments.

Bioenergetics and solute uptake under extreme conditions.

The ion and particularly the proton and sodium ion permeabilities of cytoplasmic membranes play crucial roles in the bioenergetics of microorganisms. The proton and sodium permeabilities of membranes increase with temperature. Psychrophilic and mesophilic bacteria and mesophilic, (hyper)thermophilic, and halophilic archaea are capable of adjusting the lipid composition of their membranes in such a way that the proton permeability at the respective growth temperature remains constant (homeoproton permeability). Thermophilic bacteria are an exception. They rely on the less permeable sodium ions to generate a sodium motive force, which is subsequently used to drive energy-requiring membrane-bound processes. Transport of solutes across bacterial and archaeal membranes is mainly catalyzed by primary ATP-driven transport systems or by proton- or sodium-motive-force-driven secondary transport systems. Unlike most bacteria, hyperthermophilic bacteria and archaea prefer primary uptake systems. Several high-affinity ATP-binding cassette (ABC) transporters for sugars from hyperthermophiles have been identified and characterized. The activities of these ABC transporters allow these organisms to thrive in their nutrient-poor environments.

The relative importance of photosynthesis and respiration in determining plant growth rate

The underlying physiological and biomass allocation parameters associated with differences in (RGR) among plant species characteristic of contrasting habitats have been well characterised. When grown at a single temperature under controlled environment conditions, plant species characteristic of unfavourable habitats exhibit lower RGR values than species from favourable environments. Slow growing species also exhibit lower rates of photosynthesis and respiration per unit plant mass. We examine the impact of different growth temperatures on photosynthesis and respiration and how this affects the RGR of some fast and slow growing species. Photosynthesis and respiration are both temperature sensitive in short-term experiments. Continued exposure to contrasting temperatures can, however, result in acclimation of respiration and photosynthesis. We examine the impact of different growth temperatures on photosynthesis and respiration and how this affects the RGR of a range of fast and slow growing species. Measurements of leaf level photosynthesis, leaf respiration (dark and light) and root respiration were made on 16 plant species that differed in RGR. Plants were grown hydroponically at 18, 23 and 28oC and measurements were made at the respective growth temperature. Photosynthesis and root respiration achieved homeostasis when plants were grown at the three temperatures. Leaf respiration however increased with temperature. There was a negative correlation between RGR and the percentage of daily photosynthesis respired, this relationship was maintained at all temperatures. RGR was reduced at 28oC due to a lack of acclimation of leaf respiration, which lead to an increase in ratio of respiration to photosynthesis. The importance of respiration and photosynthesis on ultimate growth rate will be discussed.

Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes

Air temperatures have risen over the past 50 yr along the Antarctic Peninsula, and it is unclear what impact this is having on Antarctic plants. We examined the growth response of the Antarctic vascular plants Colobanthus quitensis (Caryophyllaceae) and Deschampsia antarctica (Poaceae) to temperature and also assessed their ability for thermal acclimation, in terms of whole-canopy net photosynthesis (P(n)) and dark respiration (R(d)), by growing plants for 90 d under three contrasting temperature regimes: 7°C day/7°C night, 12°C day/7°C night, and 20°C day/7°C night (18 h/6 h). These daytime temperatures represent suboptimal (7°C), near-optimal (12°C), and supraoptimal (20°C) temperatures for P(n) based on field measurements at the collection site near Palmer Station along the west coast of the Antarctic Peninsula. Plants of both species grown at a daytime temperature of 20°C had greater RGR (relative growth rate) and produced 2.2-3.3 times as much total biomass as plants grown at daytime temperatures of 12° or 7°C. Plants grown at 20°C also produced 2.0-4.1 times as many leaves, 3.4-5.5 times as much total leaf area, and had 1.5-1.6 times the LAR (leaf area ratio; leaf area:total biomass) and 1.1-1.4 times the LMR (leaf mass ratio; leaf mass:total biomass) of plants grown at 12° or 7°C. Greater RGR and biomass production at 20°C appeared primarily due to greater biomass allocation to leaf production in these plants. Rates of P(n) (leaf-area basis), when measured at their respective daytime growth temperatures, were highest in plants grown at 12°C, and rates of plants grown at 20°C were only 58 (C. quitensis) or 64% (D. antarctica) of the rates in plants grown at 12°C. Thus, lower P(n) per leaf area in plants grown at 20°C was more than offset by much greater leaf-area production. Rates of whole-canopy P(n) (per plant), when measured at their respective daytime growth temperatures, were highest in plants grown at 20°C, and appeared well correlated with differences in RGR and total biomass among treatments. Colobanthus quitensis exhibited only a slight ability for relative acclimation of P(n) (leaf-area basis) as the optimal temperature for P(n) increased from 8.4° to 10.3° to 11.5°C as daytime growth temperatures increased from 7° to 12° to 20°C. There was no evidence for relative acclimation of P(n) in D. antarctica, as plants grown at all three temperature regimes had a similar optimal temperature (10°C) for P(n). There was no evidence for absolute acclimation of P(n) in either species, as rates of P(n) in plants grown at a daytime temperature of 12°C were higher than those of plants grown at daytime temperatures of 7° or 20°C, when measured at their respective growth temperatures. The poor ability for photosynthetic acclimation in these species may be associated with the relatively stable maritime temperature regime during the growing season along the Peninsula. In contrast to P(n), both species exhibited full acclimation of R(d), and rates of R(d) on a leaf-area basis were similar among treatments when measured at their respective daytime growth temperature. Our results suggest that in the absence of interspecific competition, continued warming along the Peninsula will lead to improved vegetative growth of these species due to (1) greater biomass allocation to leaf-area production (as opposed to improved rates of P(n) per leaf area) and (2) their ability to acclimate R(d), such that respiratory losses per leaf area do not increase under higher temperature regimes.

Maltose-binding protein from the hyperthermophilic bacterium Thermotoga maritima: stability and binding properties

Recombinant maltose-binding protein from Thermotoga maritima (TmMBP) was expressed in Escherichia coli and purified to homogeneity, applying heat incubation of the crude extract at 75°C. As taken from the spectral, physicochemical and binding properties, the recombinant protein is indistinguishable from the natural protein isolated from the periplasm of Thermotoga maritima. At neutral pH, TmMBP exhibits extremely high intrinsic stability with a thermal transition >105°C. Guanidinium chloride-induced equilibrium unfolding transitions at varying temperatures result in a stability maximum at ≈40°C. At room temperature, the thermodynamic analysis of the highly cooperative unfolding equilibrium transition yields Δ G N→U=100(±5) kJ mol −1 for the free energy of stabilization. Compared to mesophilic MBP from E. coli as a reference, this value is increased by about 60 kJ mol −1. At temperatures around the optimal growth temperature of T. maritima ( t opt≈80°C), the yield of refolding does not exceed 80 %; the residual 20 % are misfolded, as indicated by a decrease in stability as well as loss of the maltose-binding capacity. TmMBP is able to bind maltose, maltotriose and trehalose with dissociation constants in the nanomolar to micromolar range, combining the substrate specificities of the homologs from the mesophilic bacterium E. coli and the hyperthermophilic archaeon Thermococcus litoralis. Fluorescence quench experiments allowed the dissociation constants of ligand binding to be quantified. Binding of maltose was found to be endothermic and entropy-driven, with Δ H b =+47 kJ mol −1 and Δ S b=+257 J mol −1 K −1. Extrapolation of the linear vant’Hoff plot to t opt resulted in K d≈0.3 μM. This result is in agreement with data reported for the MBPs from E. coli and T. litoralis at their respective optimum growth temperatures, corroborating the general observation that proteins under their specific physiological conditions are in corresponding states.