An Evaluation of the Critical Parameters for Abiotic Peptide Synthesis in Submarine Hydrothermal Systems

It has been proposed that oligopeptides may be formed in submarine hydrothermal systems (SHSs). Oligopeptides have been synthesized previously under simulated SHS conditions which are likely geochemically implausible. We have herein investigated the oligomerization of glycine under SHS–like conditions with respect to the limitations imposed by starting amino acid concentration, heating time, and temperature. When 10⁻¹ M glycine solutions were heated at 250°C for < 20 min glycine oligomers up to tetramers and diketopiperazine (DKP) were detectable. At 200°C, less oligomerization was noted. Peptides beyond glycylglycine (gly₂) and DKP were not detected below 150°C. At 10⁻² M initial glycine concentration and below, only gly₂, DKP, and gly₃ were detected, and then only above 200°C at < 20 min reaction time. Gly₃ was undetectable at longer reaction times. The major parameters limiting peptide synthesis in SHSs appear to be concentration, time, and temperature. Given the expected low concentrations of amino acids, the long residence times and range of temperatures in SHSs, it is unlikely that SHS environments were robust sources of even simple peptides. Possible unexplored solutions to the problems presented here are also discussed.     

Effects of light and temperature on the attachment and development of <Emphasis Type="BoldItalic">Gloiopeltis tenax</Emphasis> and <Emphasis Type="BoldItalic">Gloiopeltis furcata</Emphasis> tetraspores

Two 60-day experiments were conducted to study the influence of photon flux density (PFD) and temperature on the attachment and development of Gloiopeltis tenax and Gloiopeltis furcata tetraspores. In the first experiment, tetraspores of the two Gloiopeltis species were incubated at five temperature ranges (8°C, 12°C, 16°C, 20°C, 24°C) under a constant PFD of 80 μmol photons m⁻² s⁻¹ with a photoperiod of 12:12. In a second experiment, tetraspores were incubated under five PFD gradients (30, 55, 80, 105, 130 μmol photons m⁻² s⁻¹) at a constant temperature of 16°C with a photoperiod of 12:12. Maximum density of attached tetraspores was observed at 16°C for both species. Maximum per cent of spore germinating into disc was recorded at 12–16°C for G. tenax and 8–12°C for G. furcata. Maximum per cent of discs producing erect axes for G. tenax and G. furcata were recorded at 24°C and 20°C, respectively. Light had no significant effect on tetraspore attachment and developing into disc, but it affected the growth, sprouting and survival of its discs. Under 30–55 μmol photons m⁻² s⁻¹, the discs of the two species of Gloiopeltis did not form thallus until the end of the experiment. Optimum PFD range for G. tenax discs was 80–105 μmol photons m⁻² s⁻¹, whilst it was 80–130 μmol photons m⁻² s⁻¹ for G. furcata. Results presented in this study are expected to assist the progress of artificial seeding of Gloiopeltis.     

Impact of two different types of heat stress on chloroplast movement and fluorescence signal of tobacco leaves

Although the chloroplast movement can be strongly affected by ambient temperature, the information about chloroplast movement especially related to high temperatures is scarce. For detailed investigation of the effects of heat stress (HS) on tobacco leaves (Nicotiana tabacum L. cv. Samsun), we used two different HS treatments in dark with wide range of elevated temperatures (25–45°C). The leaf segments were either linearly heated in water bath at heating rate of 2°C min⁻¹ from room temperature up to maximal temperature (T _m) and then linearly cooled down to 25°C or incubated for 5 min in water bath at the same T _m followed by 5 min incubation at 25°C (T-jump). The changes in light-induced chloroplast movement caused by the HS pretreatment were detected after the particular heating regime at 25°C using a method of time-dependent collimated transmittance (CT) and compared with the chlorophyll O–J–I–P fluorescence rise (FLR) measurements. The inhibition of chloroplast movement started at about 40°C while the fluorescence parameters responded generally at higher T _m. This difference in sensitivity of CT and FLR was higher for the T-jump than for the linear HS indicating importance of applied heating regime. A possible influence of chloroplast movement on the FLR measurement and a physiological role of the HS-impaired chloroplast movement are discussed.     

Ethanol and xylitol production from glucose and xylose at high temperature by <Emphasis Type="Italic">Kluyveromyces</Emphasis> sp. IIPE453

A yeast strain Kluyveromyces sp. IIPE453 (MTCC 5314), isolated from soil samples collected from dumping sites of crushed sugarcane bagasse in Sugar Mill, showed growth and fermentation efficiency at high temperatures ranging from 45°C to 50°C. The yeast strain was able to use a wide range of substrates, such as glucose, xylose, mannose, galactose, arabinose, sucrose, and cellobiose, either for growth or fermentation to ethanol. The strain also showed xylitol production from xylose. In batch fermentation, the strain showed maximum ethanol concentration of 82 ± 0.5 g l⁻¹ (10.4% v/v) on initial glucose concentration of 200 g l⁻¹, and ethanol concentration of 1.75 ± 0.05 g l⁻¹ as well as xylitol concentration of 11.5 ± 0.4 g l⁻¹ on initial xylose concentration of 20 g l⁻¹ at 50°C. The strain was capable of simultaneously using glucose and xylose in a mixture of glucose concentration of 75 g l⁻¹ and xylose concentration of 25 g l⁻¹, achieving maximum ethanol concentration of 38 ± 0.5 g l⁻¹ and xylitol concentration of 14.5 ± 0.2 g l⁻¹ in batch fermentation. High stability of the strain was observed in a continuous fermentation by feeding the mixture of glucose concentration of 75 g l⁻¹ and xylose concentration of 25 g l⁻¹ by recycling the cells, achieving maximum ethanol concentration of 30.8 ± 6.2 g l⁻¹ and xylitol concentration of 7.35 ± 3.3 g l⁻¹ with ethanol productivity of 3.1 ± 0.6 g l⁻¹ h⁻¹ and xylitol productivity of 0.75 ± 0.35 g l⁻¹ h⁻¹, respectively.     

Photosynthetic characteristics and physiological plasticity of an Aphanizomenon flos-aquae (Cyanobacteria, Nostocaceae) winter bloom in a deep oligo-mesotrophic lake (Lake Stechlin, Germany)

In winter of 2009/2010, Aphanizomenon flos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m⁻² s⁻¹ PAR at each applied temperature. The photoadaptation parameter (I _k) and the maximum photosynthetic rate (P _max) correlated positively with the temperature between 2 and 30°C, and there was a remarkable drop in both parameters at 35°C. The low I _k at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20°C at irradiances above 150 μmol m⁻² s⁻¹. At lower irradiance levels (7.5–30 μmol m⁻² s⁻¹), the photosynthesis was the most intensive in the temperature range of 2–5°C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2°C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P–I and P–T measurements provide novel information about the tolerance and physiological plasticity of this species.     

Production and characterization of esterase and lipase from <Emphasis Type="Italic">Haloarcula marismortui</Emphasis>

The present study was conducted to investigate the capability of Haloarcula marismortui to synthesize esterases and lipases, and the effect of physicochemical conditions on the growth and the production of esterases and lipases. Finally, the effect of NaCl concentration and temperature on esterase and lipase activities was studied using intracellular crude extracts. In order to confirm the genomic prediction about the esterase and lipase synthesis, H. marismortui was cultured on a rich medium and the crude extracts (intra- or extracellular) obtained were assayed for both activities using p-nitrophenyl esters and triacylglycerides as substrates. Studies on the kinetics of growth and production of esterase and lipase of H. marismortui were performed, reaching a maximum growth rate of 0.053 h⁻¹ and maximal productions of intracellular esterase and lipase of 2.094 and 0.722 U l⁻¹ using p-nitrophenyl valerate and p-nitrophenyl laurate, respectively. Both enzymes were produced as growth-associated metabolites. The effects of temperature, pH, and NaCl concentration on the growth rate and production of enzymes were studied by using a Box–Behnken response surface design. The three response variables were significantly influenced by the physicochemical factors and an interaction effect between temperature and NaCl concentration was also evidenced. The surface response method estimated the following maximal values for growth rate and productions of esterase and lipase: 0.086 h⁻¹ (at 42.5°C, pH 7.4, and 3.6 mol l⁻¹ NaCl), 2.3 U l⁻¹ (at 50°C, pH 7.5, and 4.3 mol l⁻¹ NaCl), and 0.58 U l⁻¹ (at 50°C, pH 7.6, and 4.5 mol l⁻¹ NaCl), respectively. Esterases were active at different salt concentrations, showing two optimal activities (at 0.5 and 5 mol l⁻¹ NaCl), which suggested the presence of two different esterases. Interestingly, in the absence of salt, esterase retained 50% residual activity. Esterases and lipase activities were maximal at 45°C and inactive at 75°C. This study represents the first report evidencing the synthesis of esterase and lipase by H. marismortui.     

Effect of Thermal Treatment on the Physicochemical Properties of Emulsion Stabilized by Gelatin from Black Tilapia (Oreochromis mossambicus) Skin

This study investigated the influence of thermal treatment (30 °C to 110 °C, 30 min) on the physicochemical and rheological properties of an emulsion stabilized by black tilapia (Oreochromis mossambicus) skin at pH 4. The protein pattern of tilapia gelatin did not have any significant difference after the gelatin was heated within a temperature range of 30 °C to 70 °C. However, at 90 °C and 110 °C, denaturation occurred where α-, β- and γ-chains of the gelatin were degraded, leading to a concomitant increase in low molecular peptides. The emulsion stability was investigated through a particle size analyzer, zeta potential, microscopic observation and creaming index. The gelatin emulsion was physically stable at 30 °C to 70 °C with a mean droplet size of less than 13 μm. When the heating temperature was increased to 90 °C and 110 °C, the emulsion showed a pronounced increase in droplet size due to coalescence. The gelatin emulsion heated at 90 °C and 110 °C also displayed instability against creaming after storage at room temperature for 7 days. As the heating temperature increased, the gelatin emulsion exhibited a decrease in apparent viscosity and the flow behavior changed from shear thinning to Newtonian. The rheological data also showed that the storage modulus (G′) of emulsion became more frequency dependent as the heating temperature increased, indicating weak droplet interactions. The tilapia gelatin emulsion was physically unstable when subjected to thermal treatment above 70 °C. The data reported in this study provides useful insight into the formulation of acidic food emulsions that require thermal treatment.

     

Photosynthetic response and recovery of Antarctic marine benthic microalgae exposed to elevated irradiances and temperatures

Exposure to high temperatures affects the photosynthetic processes in marine benthic microalgae by limiting the transport of electrons, thus reducing the ability of the cell to use light. This causes damage to the Photosystem II (PSII) and may lead to photoinhibition. However, the PSII of benthic microalgal communities from Brown Bay, eastern Antarctica, were relatively unaffected by significant changes in temperature. Benthic microalgae exposed to temperatures up to 8°C and an irradiance of 450 μmol photons m⁻² s⁻¹ did not experience any photosynthetic damage or irreversible photoinhibition. The effective quantum yield (∆F/F _m′) at 8°C (0.433 ± 0.042) was higher by comparison to cell incubated at −0.1°C (0.373 ± 0.015) with similar irradiances. Temperatures down to −5°C at a similar irradiance showed a decrease in photosynthesis with decreasing temperature, but no severe photoinhibition as the cells were able to dissipate excess energy via non-photochemical quenching and recover from damage. These responses are consistent with those recorded in past studies on Antarctic benthic microalgae and suggest that short-term temperature change (from −5 to 8°C) will not do irreversible damage to the PSII and will not affect the photosynthesis of the benthic microalgae.     

Irreversible changes in barley leaf chlorophyll fluorescence detected by the fluorescence temperature curve in a linear heating/cooling regime

The chlorophyll fluorescence (F) temperature curves in a linear time-temperature heating/cooling regime were used to study heat-induced irreversible F changes in primary green leaves of spring barley (Hordeum vulgare L. cv. Akcent). The leaf segments were heated in a stirred water bath at heating rates of 0.0083, 0.0166, 0.0333, and 0.0500 °C s⁻¹ from room temperature up to maximal temperature T _m and then linearly cooled to 35 °C at the same rate. The F intensity was measured by a pulse-modulated technique. The results support the existence of the two critical temperatures of irreversible F changes postulated earlier, at 45–48 and 53–55 °C. The critical temperatures are slightly dependent on the heating rate. Two types of parameters were used to characterize the irreversibility of the F changes: the coefficient of irreversibility μ defined as the ratio of F intensity at 35 °C at the starting/ending parts of the cycle and the slopes of tangents of linear parts of the F temperature curve. The dependence of μ on T _m revealed a maximum, which moved from 54 to 61 °C with the increasing heating/cooling rate v from 0.0083 to 0.0500 °C s⁻¹, showing two basic phases of the irreversible changes. The Arrhenius and Eyring approaches were applied to calculate the activation energies of the initial increase in μ. The values varied between 30 and 50 kJ mol⁻¹ and decreased slightly with the increasing heating rate.     

Performance and microbial community composition dynamics of aerobic granular sludge from sequencing batch bubble column reactors operated at 20 °C, 30 °C, and 35 °C

Two bubble column sequencing batch reactors fed with an artificial wastewater were operated at 20 °C, 30 °C, and 35 °C. In a first stage, stable granules were obtained at 20 °C, whereas fluffy structures were observed at 30 °C. Molecular analysis revealed high abundance of the operational taxonomic unit 208 (OTU 208) affiliating with filamentous bacteria Leptothrix spp. at 30 °C, an OTU much less abundant at 20 °C. The granular sludge obtained at 20 °C was used for the second stage during which one reactor was maintained at 20 °C and the second operated at 30 °C and 35 °C after prior gradual increase of temperature. Aerobic granular sludge with similar physical properties developed in both reactors but it had different nutrient elimination performances and microbial communities. At 20 °C, acetate was consumed during anaerobic feeding, and biological phosphorous removal was observed when Rhodocyclaceae-affiliating OTU 214 was present. At 30 °C and 35 °C, acetate was mainly consumed during aeration and phosphorous removal was insignificant. OTU 214 was almost absent but the Gammaproteobacteria-affiliating OTU 239 was more abundant than at 20 °C. Aerobic granular sludge at all temperatures contained abundantly the OTUs 224 and 289 affiliating with Sphingomonadaceae indicating that this bacterial family played an important role in maintaining stable granular structures.     

Elevated CO2 and temperature increase soil C losses from a soybean–maize ecosystem

Warming temperatures and increasing CO₂ are likely to have large effects on the amount of carbon stored in soil, but predictions of these effects are poorly constrained. We elevated temperature (canopy: +2.8 °C; soil growing season: +1.8 °C; soil fallow: +2.3 °C) for 3 years within the 9th–11th years of an elevated CO₂ (+200 ppm) experiment on a maize–soybean agroecosystem, measured respiration by roots and soil microbes, and then used a process‐based ecosystem model (DayCent) to simulate the decadal effects of warming and CO₂ enrichment on soil C. Both heating and elevated CO₂ increased respiration from soil microbes by ~20%, but heating reduced respiration from roots and rhizosphere by ~25%. The effects were additive, with no heat × CO₂ interactions. Particulate organic matter and total soil C declined over time in all treatments and were lower in elevated CO₂ plots than in ambient plots, but did not differ between heat treatments. We speculate that these declines indicate a priming effect, with increased C inputs under elevated CO₂ fueling a loss of old soil carbon. Model simulations of heated plots agreed with our observations and predicted loss of ~15% of soil organic C after 100 years of heating, but simulations of elevated CO₂ failed to predict the observed C losses and instead predicted a ~4% gain in soil organic C under any heating conditions. Despite model uncertainty, our empirical results suggest that combined, elevated CO₂ and temperature will lead to long‐term declines in the amount of carbon stored in agricultural soils.     

Single-wall carbon nanotube nanobomb agents for killing breast cancer cells

We report the first application of single-wall carbon nanotubes (SWCNT) as potent therapeutic nanobomb agents for killing breast cancer cells. We show here that by adsorbing water molecules in SWCNT sheets or loosely adsorbed on top of cells, potent nanobombs were created that heated the water molecules inside them to more than 100°C upon exposure to laser light of 800 nm at light intensities of approx 50–200 mW/cm². Conversion of optical energy into thermal energy, and the subsequent confinement of thermal energy in SWCNT, caused the water molecules to evaporate and develop extreme pressures in SWCNT causing them to explode in solutions. Co-localized nanobombs killed human BT474 breast cancer cells in physiological phosphate-buffered saline (PBS) solution. Cells that were treated with nanobombs exploded into fragments, while the surrounding cells not treated with nanobombs were viable. SWCNT-based nanobomb agents can potentially outperform most nanotechnological approaches in killing cancer cells without toxicity.     

Enhancement of biochemical methane potential from excess sludge with low organic content by mild thermal pretreatment

Excess sludge with low organic content always led to the failure of anaerobic digestion for methane production. Recently, the mild thermal pretreatment, which is usually operated at temperatures below 120 °C, has drawn much attention due to less energy consumption and no chemical addition. In this study the effect of mild thermal pretreatment (50–120 °C) on the solubilization and methane potential of excess sludge with a low concentration of organic matters was investigated. Experimental results showed that the concentration of soluble organic matters increased gradually with temperature during the mild thermal pretreatment of excess sludge. Biochemical methane potential experiments demonstrated that the potential of methane production from excess sludge was greatly enhanced by mild thermal pretreatment, and under the conditions of pretreatment temperature 100 °C and digestion time 20 d the methane yield was as high as 142.6 ± 2.5 mL/g of volatile solids. Mechanism investigation on the enhancement of methane production from excess sludge exhibited that the consumptions of sludge protein and carbohydrate, the adenosine 5′-triphosphate content of anaerobic microorganisms, the activities of key enzymes related to anaerobic digestion, and the amount of methanogens were all improved by mild thermal pretreatment, in correspondence with the production of methane.     

The effect of root temperature on rose plants in relation to air temperature

Rose plants (Rosa hybrida ‘Sonia’=‘Sweet Promise’) were grown in heated (minimum night temperature 17°C), and unheated greenhouses with or without root heating to 21°C. These trials covered 6 growth cycles extending over two winter seasons. In the heated greenhouse, root heating did not increase yield, flower quality or plant development. In the unheated greenhouse, root-heated plants grew as well as those in the air-heated greenhouse as long as the air temperature did not fall below 6°C. When minimum night temperatures fell below 6°C, growth, yield and quality were reduced, irrespective of root temperature. Daytime plant water relations were studied in plants growing at 6 different root temperatures in the unheated greenhouse. Leaf resistance to water diffusion was lowest at optimal root temperature. Total leaf water potential was not significantly affected by root temperature.     

Interactive effects of climate change and eutrophication on the dinoflagellate-bearing benthic foraminifer <Emphasis Type="Italic">Marginopora vertebralis</Emphasis>

Elevated sea surface temperatures caused by global climate change and increased nutrient concentrations resulting from land runoff both are stressors for calcifying coral reef organisms. Here, we test the hypothesis that increased temperature leads to bleaching in dinoflagellate-bearing foraminifera similar to corals and that increased nutrients through runoff can exaggerate stress on the holobiont. In an experiment manipulating temperatures alone, we have shown that mortality of Marginopora vertebralis increased with temperatures. Most individuals died after 7 days at 34°C, ~5°C above current summer maxima. Survival at 37 days was >98% at 28°C. After 7 days of exposure to 31 or 32°C, photosynthesis of the endosymbionts was compromised, as indicated by several photophysiological parameters (effective quantum yield and apparent photosynthetic rate). In a flow-though experiment manipulating both temperature (three levels, 26, 29 and 31°C) and nitrate concentrations (3 levels, ~0.5, 1.0 and 1.4 μmol l⁻¹ NO₃ ⁻), elevated temperature had a significant negative effect on most parameters measured. At 31°C, most photopigments (measured by UPLC) in the foraminifera were significantly reduced. The only pigment that increased was the photoprotective diatoxanthin. Several other parameters measured (maximum and effective quantum yield, O₂ production in light, organic carbon contents) also significantly decreased with temperature. Optode-based respirometry demonstrated that the presence of symbionts at elevated temperatures represents a net carbon loss for the host. Growth rates of M. vertebralis and mortality at the end of the experiment were significantly affected by both temperature increase and nitrate addition. We conclude that these foraminifera bleach in a similar fashion to corals and that global sea surface temperature change and nitrate increases are stressors for these protists. Furthermore, this provides support for the hypothesis that management of local stressors elevates resilience of coral reefs to global stressors.     

First description of the environmental niche of the epibenthic dinoflagellate species Coolia palmyrensis,C. malayensis,and C. tropicalis (Dinophyceae) from Eastern Australia

Environmental variables such as temperature, salinity, and irradiance are significant drivers of microalgal growth and distribution. Therefore, understanding how these variables influence fitness of potentially toxic microalgal species is particularly important. In this study, strains of the potentially harmful epibenthic dinoflagellate species Coolia palmyrensis, C. malayensis, and C. tropicalis were isolated from coastal shallow water habitats on the east coast of Australia and identified using the D1‐D3 region of the large subunit (LSU) ribosomal DNA (rDNA). To determine the environmental niche of each taxon, growth was measured across a gradient of temperature (15–30°C), salinity (20–38), and irradiance (10–200 μmol photons · m^?2 · s^?1). Specific growth rates of Coolia tropicalis were highest under warm temperatures (27°C), low salinities (ca. 23), and intermediate irradiance levels (150 μmol photons · m^?2 · s^?1), while C. malayensis showed the highest growth at moderate temperatures (24°C) and irradiance levels (150 μmol photons · m^?2 · s^?1) and growth rates were consistent across the range of salinity levels tested (20–38). Coolia palmyrensis had the highest growth rate of all species tested and favored moderate temperatures (24°C), oceanic salinity (35), and high irradiance (>200 μmol photons · m^?2 · s^?1). This is the first study to characterize the environmental niche of species from the benthic harmful algal bloom genus Coolia and provides important information to help define species distributions and inform risk management.     

Towards a reduction in excess sludge production in activated sludge processes: biomass physicochemical treatment and biodegradation

To decrease activated sludge production, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline, acid) were studied to generate Alcaligenes eutrophus and sludge lysates and to evaluate their biodegradability. Gentle treatment conditions produced the best results. Complete cell deactivation was obtained for temperatures higher than 55 °C. The release kinetics were similar for temperatures varying from 60 °C to 100 °C. A 20-min incubation was suitable for reaching 80% of the maximum releasable carbon. In thermal-chemical hydrolysis, NaOH was the most efficient for inducing cell lysis. Carbon release was a two-step process. First an immediate release occurred, which was of the same order of magnitude for A. eutrophus and sludge [100–200 mg dissolved organic C (DOC) g total suspended solids (TSS)⁻¹], followed by a post-treatment release. The second step was virtually equivalent to the first for sludge, and weaker for A. eutrophus (<50 mg DOC g TSS⁻¹). The biodegradability of the soluble fraction, both the immediate and the post-treatment carbon release, was investigated. The optimal degradation yield, obtained with sludge cells, reached 55% after 48 h of incubation and 80% after 350 h. The most consistent lysis and biodegradation results occurred at pH 10 and 60 °C after a 20-min incubation. Received: 30 October 1998 / Received revision: 16 February 1999 / Accepted: 20 February 1999     

Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat

New technologies afford convenient modalities for skin temperature (T_SKIN) measurement, notably involving wireless telemetry and non-contact infrared thermometry. The purpose of this study was to investigate the validity and reliability of skin temperature measurements using a telemetry thermistor system (TT) and thermal camera (TC) during exercise in a hot environment. Each system was compared against a certified thermocouple, measuring the surface temperature of a metal block in a thermostatically controlled waterbath. Fourteen recreational athletes completed two incremental running tests, separated by one week. Skin temperatures were measured simultaneously with TT and TC compared against a hard-wired thermistor system (HW) throughout rest and exercise. Post hoc calibration based on waterbath results displayed good validity for TT (mean bias [MB]=−0.18 °C, typical error [TE]=0.18 °C) and reliability (MB=−0.05 °C, TE=0.31 °C) throughout rest and exercise. Poor validity (MB=−1.4 °C, TE=0.35 °C) and reliability (MB=−0.65 °C, TE=0.52 °C) was observed for TC, suggesting it may be best suited to controlled, static situations. These findings indicate TT systems provide a convenient, valid and reliable alternative to HW, useful for measurements in the field where traditional methods may be impractical.     

Characterization of PSI recovery after chilling-induced photoinhibition in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) leaves

By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the effects of different photon flux densities (0, 15, 200 μmol m⁻² s⁻¹) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber (Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m⁻² s⁻¹) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) (F _v/F _m) and the content of active P700 (ΔI/I _o) significantly decreased after chilling treatment under 200 μmol m⁻² s⁻¹ light. After the leaves were transferred to 25°C, F _v/F _m recovered quickly under both 200 and 15 μmol m⁻² s⁻¹ light. ΔI/I _o recovered quickly under 15 μmol m⁻² s⁻¹ light, but the recovery rate of ΔI/I _o was slower than that of F _v/F _m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of ΔI/I _o was severely suppressed by 200 μmol m⁻² s⁻¹ light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU. The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery of PSI or even to the whole photosystem.     

Effect of temperature on <Emphasis Type="SmallCaps">d</Emphasis>-arabitol production from lactose by <Emphasis Type="Italic">Kluyveromyces lactis</Emphasis>

d-Arabitol production from lactose by Kluyveromyces lactis NBRC 1903 has been studied by following the time courses of concentrations of cell mass, lactose, d-arabitol, ethanol, and glycerol at different temperatures. It was found that temperature is a key factor in d-arabitol production. Within temperatures ranging from 25 to 39°C, the highest d-arabitol concentration of 99.2 mmol l⁻¹ was obtained from 555 mmol l⁻¹ of lactose after 120 h of batch cultivation at 37°C. The yield of d-arabitol production on cell mass growth increased drastically at temperatures higher than 35°C, and the yield reached 1.07 at 39°C. Increasing the cell mass concentration two-fold after 24 h of culture growth at 37°C, the d-arabitol concentration further increased to 168 mmol l⁻¹. According to the distribution of the metabolic products, metabolic changes related to growth phase were also discussed. The stationary-phase K. lactis cells in the batch culture that is started with exposing the precultured inoculum to high osmotic stress, high oxidative stress, and high heat stress are found to be preferable for d-arabitol production.