Cold hardiness of diapausing and non-diapausing pupae of the European grapevine moth, Lobesia botrana

Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae) is a key pest of grapes in Europe. It overwinters as a pupa in the bark crevices of the plant. Supercooling point (SCP) and low temperature survival was investigated in the laboratory and was determined using a cool bath and a 1 °C min^?1 cooling rate. Freezing was fatal both to diapausing and non‐diapausing pupae. SCP was significantly lower in diapausing male (?24.8 °C) and female (?24.5 °C) pupae than in non‐diapausing ones (?22.7 and ?22.5 °C, respectively). Sex had no influence on SCP both for diapausing and non‐diapausing pupae. Supercooling was also not affected by acclimation. However, acclimation did improve survival of diapausing pupae at temperatures above the SCP. Survival increased as acclimation period increased and the influence was more profound at the lower temperatures examined. Diapausing pupae could withstand lower temperatures than non‐diapausing ones and lethal temperature was significantly lower than for non‐diapausing pupae. Freezing injury above the SCP has been well documented for both physiological stages of L. botrana pupae. Our findings suggest a diapause‐related cold hardiness for L. botrana and given its cold hardiness ability, winter mortality due to low temperatures is not expected to occur, especially in southern Europe.     

Effects of elevated temperature and carbon dioxide on seed-set and yield of kidney bean (Phaseolus vulgaris L.)

It is important to quantify and understand the consequences of elevated temperature and carbon dioxide (CO₂) on reproductive processes and yield to develop suitable agronomic or genetic management for future climates. The objectives of this research work were (a) to quantify the effects of elevated temperature and CO₂ on photosynthesis, pollen production, pollen viability, seed‐set, seed number, seeds per pod, seed size, seed yield and dry matter production of kidney bean and (b) to determine if deleterious effects of high temperature on reproductive processes and yield could be compensated by enhanced photosynthesis at elevated CO₂ levels. Red kidney bean cv. Montcalm was grown in controlled environments at day/night temperatures ranging from 28/18 to 40/30 °C under ambient (350 µmol mol^?1) or elevated (700 µmol mol^?1) CO₂ levels. There were strong negative relations between temperature over a range of 28/18–40/30 °C and seed‐set (slope, ? 6.5% °C^?1) and seed number per pod (? 0.34 °C^?1) under both ambient and elevated CO₂ levels. Exposure to temperature > 28/18 °C also reduced photosynthesis (? 0.3 and ? 0.9 µmol m^?2 s^?1 °C^?1), seed number (? 2.3 and ? 3.3 °C^?1) and seed yield (? 1.1 and ? 1.5 g plant^?1 °C^?1), at both the CO₂ levels (ambient and elevated, respectively). Reduced seed‐set and seed number at high temperatures was primarily owing to decreased pollen production and pollen viability. Elevated CO₂ did not affect seed size but temperature > 31/21 °C linearly reduced seed size by 0.07 g °C^?1. Elevated CO₂ increased photosynthesis and seed yield by approximately 50 and 24%, respectively. There was no beneficial interaction of CO₂ and temperature, and CO₂ enrichment did not offset the negative effects of high temperatures on reproductive processes and yield. In conclusion, even with beneficial effects of CO₂ enrichment, yield losses owing to high temperature (> 34/24 °C) are likely to occur, particularly if high temperatures coincide with sensitive stages of reproductive development.     

THE EFFECTS OF TEMPERATURE ON THE PHOTOSYNTHETIC PARAMETERS AND RECOVERY OF TWO TEMPERATE BENTHIC MICROALGAE,AMPHORA CF. COFFEAEFORMIS AND COCCONEIS CF. SUBLITTORALIS (BACILLARIOPHYCEAE)1

Temperature and irradiance are the most important factors affecting marine benthic microalgal photosynthetic rates in temperate intertidal areas. Two temperate benthic diatoms species, Amphora cf. coffeaeformis (C. Agardh) Kütz. and Cocconeis cf. sublittoralis Hendey, were investigated to determine how their photosynthesis responded to temperatures ranging from 5°C to 50°C after short‐term exposure (1 h) to a range of irradiance levels (0, 500, and 1,100 μmol photons · m^?2 · s^?1). Significant differences were observed between the temperature responses of maximum relative electron transport rate (rETRmax), photoacclimation index (E_k), photosynthetic efficiency (α), and effective quantum yield (ΔF/F_m’) in both species. A. coffeaeformis had a greater tolerance to higher temperatures than C. sublittoralis, with nonphotochemical quenching (NPQ) activated at temperatures of 45°C and 50°C. C. sublittoralis, however, demonstrated a more rapid rate of recovery at ambient temperatures. Temperatures between 10°C and 20°C were determined to be optimal for photosynthesis for both species. High temperatures and irradiances caused a greater decrease in ΔF/F_m’ values. These results suggest that the effects of temperature are species specific and that short‐term exposure to adverse temperature slows the recovery process, which subsequently leads to photoinhibition.     

Temperature dependence of nitrate reductase activity in marine phytoplankton: biochemical analysis and ecological implications

The temperature dependence of NADH:NR activity was examined in several marine phytoplankton species and vascular plants. These species inhabit divergent thermal environments, including the chromophytes Skeletonema costatum (12–15° C), Skeletonema tropicum (18–25° C), Thalassiosira antarctica (?2 to 4° C), and Phaeocystis antarctica (?2 to 4° C), the green alga Dunaliella tertiolecta (14–28° C), and the vascular plants Cucurbita maxima (20–35° C) and Zea mays (20–25° C). Despite the difference in growth habitats, similar temperature response curves were observed among the chromophytic phytoplankton, with temperatures optimal for NR activity being between 10–20° C. In contrast, the chlorophyll b‐containing alga and vascular plants exhibited optimal temperatures for NR activity above 30° C. Such dramatic differences in NR thermal characteristics from the two taxonomic groups reflect a divergence in NR structure that may be associated with the evolutionary diversification of chromophytes and chlorophytes. Further, it suggests a potential contribution of the thermal performance of NR to the geographic distributions, seasonal abundance patterns, and species composition of phytoplankton communities. NR partial activities, which assess the individual functions of Mo‐pterin and FAD domains, were evaluated on NR purified from S. costatum to determine the possible causes for high temperature (>20° C) inactivation of NR from chromophytes. It was found that the FAD domain and electron transport among redox centers were sensitive to elevated temperatures. S. costatum cells grown at 5, 15, and 25° C exhibited an identical optimal temperature (15° C) for NADH:NR activity, whereas the maximal NR activity and NR protein levels differed and were positively correlated with growth temperature and growth rate. These findings demonstrate that thermal acclimation of NO₃^? reduction capacity is largely at the level of NR protein expression. The consequences of these features on NO₃^? utilization are discussed.     

Investigations on the interactions of DiAmsar with serum albumins: Insights from spectroscopic and molecular docking techniques

Diamine‐sarcophagine (DiAmsar) binding to human serum albumin (HSA) and bovine serum albumin (BSA) was investigated under simulative physiological conditions. Fluorescence spectra in combination with Fourier transform infrared (FT‐IR), UV‐visible (UV–vis) spectroscopy, cyclic voltammetry (CV), and molecular docking method were used in the present work. Experimental results revealed that DiAmsar had an ability to quench the HSA and BSA intrinsic fluorescence through a static quenching mechanism. The Stern–Volmer quenching rate constant (K_sv) was calculated as 0.372 × 10³ M^‐1 and 0.640 × 10³ M^‐1 for HSA and BSA, respectively. Moreover, binding constants (K_a), number of binding sites (n) at different temperatures, binding distance (r), and thermodynamic parameters (?H°, ?S°, and ?G°) between DiAmsar and HSA (or BSA) were calculated. DiAmsar exhibited good binding propensity to HSA and BSA with relatively high binding constant values. The positive ?H° and ?S° values indicated that the hydrophobic interaction is main force in the binding of the DiAmsar to HSA (or BSA). Furthermore, molecular docking results revealed the possible binding site and the microenvironment around the bond. Copyright © 2014 John Wiley & Sons, Ltd.     

High-temperature inhibition of photosynthesis is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedling

The survival of dipterocarp seedlings in the understorey of south‐east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. Field measurements demonstrated that Shorea leprosula seedlings in a rain forest understorey received a high proportion of daily photon flux density at temperatures supra‐optimal for photosynthesis (72% at ≥30 °C, 14% at ≥35 °C). To investigate the effect of high temperatures on photosynthesis during sunflecks, gas exchange and chlorophyll fluorescence measurements were made on seedlings grown in controlled environment conditions either, under uniform, saturating irradiance (approximately 539 µmol m^?2 s^?1) or, shade/fleck sequences (approximately 30 µmol m^?2 s^?1/approximately 525 µmol m^?2 s^?1) at two temperatures, 28 or 38 °C. The rate of light‐saturated photosynthesis, under uniform irradiance, was inhibited by 40% at 38 °C compared with 28 °C. However, during the shade/fleck sequence, photosynthesis was inhibited by 59% at 38 °C compared with 28 °C. The greater inhibition of photosynthesis during the shade/fleck sequence, when compared with uniform irradiance, was driven by the lower efficiency of dynamic photosynthesis combined with lower steady‐state rates of photosynthesis. These results suggest that, contrary to current dogma, sunfleck activity may not always result in significant carbon gain. This has important consequences for seedling regeneration processes in tropical forests as well as for leaves in other canopy positions where sunflecks make an important contribution to total photon flux density.     

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.     

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.     

An insight into the thermodynamic characteristics of human thrombopoietin complexation with TN1 antibody

Human thrombopoietin (hTPO) primarily stimulates megakaryocytopoiesis and platelet production and is neutralized by the mouse TN1 antibody. The thermodynamic characteristics of TN1 antibody–hTPO complexation were analyzed by isothermal titration calorimetry (ITC) using an antigen‐binding fragment (Fab) derived from the TN1 antibody (TN1‐Fab). To clarify the mechanism by which hTPO is recognized by TN1‐Fab the conformation of free TN1‐Fab was determined to a resolution of 2.0 Å using X‐ray crystallography and compared with the hTPO‐bound form of TN1‐Fab determined by a previous study. This structural comparison revealed that the conformation of TN1‐Fab does not substantially change after hTPO binding and a set of 15 water molecules is released from the antigen‐binding site (paratope) of TN1‐Fab upon hTPO complexation. Interestingly, the heat capacity change (ΔCp) measured by ITC (?1.52 ± 0.05 kJ mol^?1 K^?1) differed significantly from calculations based upon the X‐ray structure data of the hTPO‐bound and unbound forms of TN1‐Fab (?1.02 ～ 0.25 kJ mol^?1 K^?1) suggesting that hTPO undergoes an induced‐fit conformational change combined with significant desolvation upon TN1‐Fab binding. The results shed light on the structural biology associated with neutralizing antibody recognition.     

Measurement of cooling and warming rates in vitrification‐based plant cryopreservation protocols

Cryopreservation protocols include the use of additives and pretreatments aimed to reduce the probability of ice nucleation at all temperatures, mainly through micro‐viscosity increase. Still, there is a risk of ice formation in the temperature region comprised between the equilibrium freezing (T_f) and the glass transition (T_G) temperatures. Consequently, fast cooling and warming, especially in this region, is a must to avoid ice‐derived damage. Vitrification and droplet‐vitrification techniques, frequently used cryopreservation protocols based in fast cooling, were studied, alongside with the corresponding warming procedures. A very fast data acquisition system, able to read very low temperatures, down to that of liquid nitrogen, was employed. Cooling rates, measured between ?20°C and ?120°C, ranged from ca. 5°C s^?1 to 400°C s^?1, while warming rates spanned from ca. 2°C s^?1 to 280°C s^?1, for the different protocols and conditions studied. A wider measuring window (0°C to ?150°C) produced lower rates for all cases. The cooling and warming rates were also related to the survival observed after the different procedures. Those protocols with the faster rates yielded the highest survival percentages. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1177–1184, 2014     

Photosynthetic response of Nereocystis luetkeana (Phaeophyta) to high light

Photosynthetic response to high light was determined for Bull kelp, Nereocystis luetkeana (K. Mertens) Postels and Ruprecht in order to understand how this species is affected by short‐term fluctuations in irradiance. Exposure of N. luetkeana blades to high intensity photosynthetically active radiation (1000 µmol photons m^?2 s^–1) caused increased non‐photochemical quenching of fluorescence and higher de‐epoxidation ratios for xanthophyll pigments indicating that energy‐quenching xanthophylls were used to protect blades against photoinhibition. Despite initiation of these photoprotective mechanisms, maximum photochemical efficiency of photosystem II (F_v/F_m) decreased 40% in response to a 60 min exposure to 1000 µmol photons m^?2 s^–1 photosynthetically active radiation indicating that photoinhibition had occurred. Light‐saturated rates of oxygen evolution were not changed significantly by the high light treatment. Recovery of maximum photochemical efficiency of photosystem II to within 8% of initial values occurred after a 300‐min dim light period. Younger sections of the blades were slightly more susceptible to high light damage than older sections. Middle sections of the blades were more prone to light‐induced damage at water temperatures of 7°C or 18°C, as compared to 13°C. Exposure to biologically effective ultraviolet‐B radiation (UV‐B_be) (up to 4.5 kJ m^–2 day^–1) in photoinhibitory light conditions did not significantly affect light‐induced damage to photosystem II.     

Temperature‐dependent phagotrophy and phototrophy in a mixotrophic chrysophyte

The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m^?2 · s^?1, with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m^?2 · s^?1). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m^?2 · s^?1), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%–30% of the carbon budget could be attributed to bacterivory at low temperatures. Grazing experiments in nutrient‐modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.     

PRELIMINARY EVALUATION OF THE BIOREMEDIATION POTENTIAL OF PORPHYRA: PHOTOSYNTHETIC PRODUCTION BY BLADES AND CONCHOCELIS

Given their rapid growth and nutrient assimilation rates, Porphyra spp. are good candidates for bioremediation. The production potential of two northeast U.S. Porphyra species currently in culture (P. purpurea and P. umbilicalis) was evaluated by measuring rates of photosynthesis (as O₂ evolution) of samples grown at 20° C. Gametophytes of P. umbilicalis photosynthesized at rates that were 80% higher than those of P. purpurea over 5–20° C at both sub‐saturating and saturating irradiances (37 and 289 μmol photons m^?2 s^?1). Porphyra umbilicalis was both more efficient at low irradiances (higher alpha) and had a higher P_max than did P. purpurea (23.0 vs. 15.6 μmol O₂ g^?1 DW min^?1), suggesting that P. umbilicalis is a better choice for mass culture where self‐shading may be severe. The photosynthesis‐irradiance relationship for the Conchocelis stage of P. purpurea was also examined. Tufts of filaments, grown at 10, 15, and 20° C, were assayed at growth temperatures at irradiances ranging from 0–315 μmol photons m^?2 s^?1. Tufts were slightly more productive at 15° than at 10° C, but only ca. 4–6% as productive as gametophytes. Maximum rates of net photosynthesis were reduced by 66–74% in tufts grown at 20° C (only about 2% of gametophytes). The Conchocelis stage, however, need not limit mariculture operations; once Conchocelis cultures are established, they can be maintained over the long‐term as ready sources of spores for net seeding.     

Chlorophyll fluorescence quenching and violaxanthin deepoxidation of FBPase antisense plants at low light intensities and low temperatures

Genetically modified potato (Solanum tuberosum L. cv. Desiree) and tobacco (Nicotiana tabacum cv. Samsun N.N.) plants were used to analyze the effects exerted by the chloroplastic (cp) fructose- 1,6-bisphosphatase (FBPase) on the regulation of light energy discrimination at the level of photosystem II. The cp-FBPase activity was progressively inhibited by an mRNA antisense to this FBPase. The chlorophyll fluorescence quenching parameters of these transgenic plants were compared to those of wild-type and transgenic plants that were acclimated to low temperatures. In particular various lines of the transgenic potato and tobacco plants were exposed to a temperature treatment of 10 and 20°C for 10 days. Light intensities were kept low to reduce photoinhibition so that we could analyze exclusively the effects of a modification in the carbon fixation cycle on the chlorophyll fluorescence quenching parameters. The photon flux densities (PFDs) employed at the level of the middle leaves of all plants were set to two different values of 10 μmol m^?2 s^?1 and 50 μmol m^?2 s^?1. Subsequent to this 10-day acclimation the chlorophyll-fluorescence parameters of all plants were measured. Photoinhibition as expressed by the F_y/F_m ratio was minor in plants subjected to a PFD of 10 μmol m^?2 s^?1. Higher photon fluence rates of 50 μmol m^?2 s^?1 at temperatures of 10°C gave rise to a significant reduction in the F_y/F_m ratios obtained from the transgenic plants which were characterized by a restriction in cp-FBPase capacity to 20% of normal activity. Furthermore, a progressive inhibition of the cp-FBPase activity induced an amplified nonphotochemical quenching of chlorophyll fluorescence with in the genetically manipulated species (except at 10°C and 50 μmol m^?2 s^?1). The increase in nonphotochemical quenching depended upon light and temperature. Photochemical quenching of light quanta within the antisense plants declined relative to that in the wild type. To further characterize the mechanisms producing higher levels of nonphotochemical fluorescence quenching. we analyzed several of the xanthophyll cycle pigments. The deepoxidation state of the xanthophyll cycle pigments in potato plants increased with attenuating FBPase activities under all conditions. For tobacco plants, this elevation of the deepoxidation state was only observed at a PFD of 50 μmol m^?2 s^?1.     

Photosynthetic downregulation in leaves of the Japanese white birch grown under elevated CO2 concentration does not change their temperature‐dependent susceptibility to photoinhibition

To determine the effects of elevated CO₂ concentration ([CO₂]) on the temperature‐dependent photosynthetic properties, we measured gas exchange and chlorophyll fluorescence at various leaf temperatures (15, 20, 25, 30, 35 and 40°C) in 1‐year‐old seedlings of the Japanese white birch (Betula platyphylla var. japonica), grown in a phytotron under natural daylight at two [CO₂] levels (ambient: 400 µmol mol^?1 and elevated: 800 µmol mol^?1) and limited N availability (90 mg N plant^?1). Plants grown under elevated [CO₂] exhibited photosynthetic downregulation, indicated by a decrease in the carboxylation capacity of Rubisco. At temperatures above 30°C, the net photosynthetic rates of elevated‐CO₂‐grown plants exceeded those grown under ambient [CO₂] when compared at their growth [CO₂]. Electron transport rates were significantly lower in elevated‐CO₂‐grown plants than ambient‐CO₂‐grown ones at temperatures below 25°C. However, no significant difference was observed in the fraction of excess light energy [(1 ? q_P)× F_v′/F_m′] between CO₂ treatments across the temperature range. The quantum yield of regulated non‐photochemical energy loss was significantly higher in elevated‐CO₂‐grown plants than ambient, when compared at their respective growth [CO₂] below 25°C. These results suggest that elevated‐CO₂‐induced downregulation might not exacerbate the temperature‐dependent susceptibility to photoinhibition, because reduced energy consumption by electron transport was compensated for by increased thermal energy dissipation at low temperatures.     

Heat stress adaptation of Escherichia coli under dynamic conditions: effect of inoculum size*

Aims: When subjected to dynamic temperatures surpassing the expected maximum growth temperature, Escherichia coli K12 MG1655 shows disturbed growth curves. These irregular population dynamics were explained by considering two subpopulations, i.e. a thermoresistant and a thermosensitive one ( Van Derlinden et al. 2010a ). In this paper, the influence of the initial cell concentration on the subpopulations’ dynamics is evaluated. Methods and Results: Experiments were performed in a bioreactor with the temperature increasing from 42 to 65·2°C (1 and 4°C h^?1) with varying initial cell concentrations [6, 12 and 18 ln(CFU ml^?1)]. When started from the highest cell concentration, the population was characterized by a higher overall maximum growth temperature and a higher inactivation temperature. For all experimental set‐ups, resistant cells were still growing at the final temperature of 65·2°C. Conclusions: The initial cell concentration had no effect on temperature resistance. The increase in temperature resistance of the sensitive subpopulation was because of the change of the physiological state to the stationary phase. Significance and Impact of the Study: A higher initial cell concentration leads to higher heat stress adaptation when cultures reach a maximum cell concentration. The observed growth at a temperature of 65·2°C is very important for food safety and the temperature treatment of micro‐organisms.     

The relative impacts of daytime and night-time warming on photosynthetic capacity in Populus deltoides

In order to investigate the relative impacts of increases in day and night temperature on tree carbon relations, we measured night‐time respiration and daytime photosynthesis of leaves in canopies of 4‐m‐tall cottonwood (Populus deltoides Bartr. ex Marsh) trees experiencing three daytime temperatures (25, 28 or 31 °C) and either (i) a constant nocturnal temperature of 20 °C or (ii) increasing nocturnal temperatures (15, 20 or 25 °C). In the first (day warming only) experiment, rates of night‐time leaf dark respiration (R_dark) remained constant and leaves displayed a modest increase (11%) in light‐saturated photosynthetic capacity (A_max) during the day (1000–1300 h) over the 6 °C range. In the second (dual night and day warming) experiment, R_dark increased by 77% when nocturnal temperatures were increased from 15 °C (0·36 µmol m^?2 s^?1) to 25 °C (0·64 µmol m^?2 s^?1). A_max responded positively to the additional nocturnal warming, and increased by 38 and 64% in the 20/28 and 25/31 °C treatments, respectively, compared with the 15/25 °C treatment. These increases in photosynthetic capacity were associated with strong increases in the maximum carboxylation rate of rubisco (V_cmax) and ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity mediated by maximum electron transport rate (J_max). Leaf soluble sugar and starch concentration, measured at sunrise, declined significantly as nocturnal temperature increased. The nocturnal temperature manipulation resulted in a significant inverse relationship between A_max and pre‐dawn leaf carbohydrate status. Independent measurements of the temperature response of photosynthesis indicated that the optimum temperature (T_opt) acclimated fully to the 6 °C range of temperature imposed in the daytime warming. Our findings are consistent with the hypothesis that elevated night‐time temperature increases photosynthetic capacity during the following light period through a respiratory‐driven reduction in leaf carbohydrate concentration. These responses indicate that predicted increases in night‐time minimum temperatures may have a significant influence on net plant carbon uptake.     

Monoterpene ‘thermometer’ of tropical forest‐atmosphere response to climate warming

Tropical forests absorb large amounts of atmospheric CO₂ through photosynthesis but elevated temperatures suppress this absorption and promote monoterpene emissions. Using ¹³CO₂ labeling, here we show that monoterpene emissions from tropical leaves derive from recent photosynthesis and demonstrate distinct temperature optima for five groups (Groups 1–5), potentially corresponding to different enzymatic temperature‐dependent reaction mechanisms within β‐ocimene synthases. As diurnal and seasonal leaf temperatures increased during the Amazonian 2015 El Niño event, leaf and landscape monoterpene emissions showed strong linear enrichments of β‐ocimenes (+4.4% °C^?1) at the expense of other monoterpene isomers. The observed inverse temperature response of α‐pinene (?0.8% °C^?1), typically assumed to be the dominant monoterpene with moderate reactivity, was not accurately simulated by current global emission models. Given that β‐ocimenes are highly reactive with respect to both atmospheric and biological oxidants, the results suggest that highly reactive β‐ocimenes may play important roles in the thermotolerance of photosynthesis by functioning as effective antioxidants within plants and as efficient atmospheric precursors of secondary organic aerosols. Thus, monoterpene composition may represent a new sensitive ‘thermometer’ of leaf oxidative stress and atmospheric reactivity, and therefore a new tool in future studies of warming impacts on tropical biosphere‐atmosphere carbon‐cycle feedbacks.     

Photosynthetic performance and resistance to photoinhibition of Zea mays L. leaves grown at sub-optimal temperature

The performance of the photosynthetic apparatus was examined in the third leaves of Zea mays L. seedlings grown at near-optimal (25 °C) or at suboptimal (15 °C) temperature by measuring chlorophyll (ChI) a fluorescence parameters and oxygen evolution in different temperature and light conditions. In leaf tissue grown at 25 and 15 °C, the quantum yield of PSII electron transport (ψ_PSII) and the rate of O₂ evolution decreased with decreasing temperature (from 25 to 4 °C) at a photon flux density of 125 μmol m^?2 s^?1. In leaves grown at 25 °C, the decrease of ψ_PSII correlated with a decrease of photochemical ChI fluorescence quenching (q_p), whereas in leaves crown at 15 °C q_p was largely insensitive to the temperature decrease. Compared with leaves grown at 25 °C, leaves grown at 15 °C were also able to maintain a higher fraction of oxidized to reduced Q_A (greater q_p) at high photon flux densities (up to 2000 μmol m^?2 s^?1), particularly when the measurements were performed at high temperature (25 °C). With decreasing temperature and/or increasing light intensity, leaves grown at 15 °C exhibited a substantial quenching of the dark level of fluorescence F₀ (q₀) whereas this type of quenching was virtually absent in leaves grown at 25 °C. Furthermore, leaves grown at 15 °C were able to recover faster from photo inhibition of photosynthesis after a photoinhibitory treatment (1200 μmol m^?2 s^?1 at 25, 15 or 6 °C for 8 h) than leaves grown at 25 °C. The results suggest that, in spite of having a low photosynthetic capacity, Z. mays leaves grown at sub optimal temperature possess efficient mechanisms of energy dissipation which enable them to cope better with photoinhibition than leaves grown at near-optimal temperature. It is suggested that the resistance of Z. mays leaves grown at 15 °C to photoinhibition is related to the higher content of carotenoids of the xanthophyll cycle (violaxanthin + antheraxanthin + zeaxanthin) measured in these leaves than in leaves grown at 25 °C.