Temperature response of C4 species big bluestem (Andropogon gerardii) is modified by growing carbon dioxide concentration

Climate change factors interact to modify plant growth and development. The objective of this study was to evaluate the response to temperature of big bluestem (Andropogon gerardii Vitman) development, growth, reproduction and biomass partitioning under low and high carbon dioxide concentrations ([CO₂]) grown in controlled environmental conditions. Ten sunlit soil–plant–atmosphere-research (SPAR) chambers were used to study the effects of two [CO₂] of low (360 μL L⁻¹) and high (720 μL L⁻¹), and five different day/night temperatures of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Big bluestem cv. Bonelli seeds were sown in pure, fine sand, in 11 rows at equal spacing and after emergence were thinned to 10 plants per row. At maturity, individual plants were harvested and divided into leaves, stems, panicles and roots. Biomass decreased either above or below the optimum temperature of 30/22 °C. The effect of high [CO₂] on biomass accumulation (12–30% increase) was visible at less than optimum temperature (30/22 °C) and absent at two high temperatures. With increase in temperature, irrespective of the [CO₂], biomass partitioned to leaves increased (35%) where as that to stems decreased (33%). Panicle weight was 6–7% of biomass at 25/17 °C and fell to 1.6% at 40/32 °C. The biomass partitioned to roots, across the temperatures, was constant for plants grown at low [CO₂] but decreased by 7% for those grown at high [CO₂]_. The decrease in panicle/seed production at two high temperatures (>30/22 °C) might reduce this species population and dominance in tallgrass prairies. The temperature response functions at different [CO₂] will be useful to improve the predictive capabilities of dynamic global vegetation models in simulating dynamics of rangelands, where big bluestem is the dominant species.     

Plasticity of rice tiller production is related to genotypic variation in the biomass response to elevated atmospheric CO2 concentration and low temperatures during vegetative growth

Appropriate resource partitioning to either production of new tillers or growth of individual tillers is a critical factor for increasing rice biomass production and facilitating adaptation to climate change. We examined the contributions of genotypic variation to the tiller number and individual tiller growth of 24 rice cultivars in response to an elevated atmospheric CO₂ concentration [CO₂] (control + 191 μmol mol⁻¹) and a low air temperature (control minus 4.7 °C) during 56 days of vegetative growth after transplanting. For all genotypes combined, biomass increased by 27% under elevated [CO₂] and decreased by 34% at low temperature, with a significant genotype × temperature interaction. The increase caused by elevated [CO₂] resulted from increased tiller number, and the decrease caused by low temperature resulted from decreased growth of individual tillers. Despite the different overall responses to elevated [CO₂] and low temperature, most of the genotypic variation in biomass at elevated [CO₂] and low temperature was explained by the responses of tiller number rather than by individual tiller growth. The genotypes with the highest biomass response to elevated [CO₂] had a smaller reduction of biomass under low temperature. These results highlight the greater importance of genotypic variation in tiller number than in individual tiller growth in the response of biomass to environmental change.     

Temperature cycle amplitude alters the adult eclosion time and expression pattern of the circadian clock gene period in the onion fly

Soil temperature cycles are considered to play an important role in the entrainment of circadian clocks of underground insects. However, because of the low conductivity of soil, temperature cycles are gradually dampened and the phase of the temperature cycle is delayed with increasing soil depth. The onion fly, Delia antiqua, pupates at various soil depths, and its eclosion is timed by a circadian clock. This fly is able to compensate for the depth-dependent phase delay of temperature change by advancing the eclosion time with decreasing amplitude of the temperature cycle. Therefore, pupae can eclose at the appropriate time irrespective of their location at any depth. However, the mechanism that regulates eclosion time in response to temperature amplitude is still unknown. To understand whether this mechanism involves the circadian clock or further downstream physiological processes, we examined the expression patterns of period (per), a circadian clock gene, of D. antiqua under temperature cycles that were square wave cycles of 12-h warm phase (W) and 12-h cool phase (C) with the temperature difference of 8 °C (WC 29:21 °C) and 1 °C (WC 25.5:24.5 °C). The phase of oscillation in per expression was found to commence 3.5 h earlier under WC 25.5:24.5 °C as compared to WC 29:21 °C. This difference was in close agreement with the eclosion time difference between the two temperature cycles, suggesting that the mechanism that responds to the temperature amplitude involves the circadian clock.     

Growth and development of cotton (Gossypium hirsutum L.) in response to CO2 enrichment under two different temperature regimes

An increase in atmospheric CO₂ concentration ([CO₂]) together with other climate change factors could greatly affect agricultural productivity. Understanding the impact of the change in atmospheric [CO₂] in conjunction with the ongoing global change is crucial to prepare for mitigation and any adaptation for future agricultural production. The main goal of this project was to study the time-course pattern of cotton plant growth in response to [CO₂] and temperature to investigate the hypothesis that whether response to elevated [CO₂] would change at different temperatures. An experiment was conducted in the controlled-environment chambers of the Georgia Envirotron with two different day/night temperatures levels, e.g., 25/15 °C and 35/25 °C, and three CO₂ concentrations, e.g., 400, 600 and 800 μmol l^?1. The experimental design was completely randomized with four replicates (plastic containers) per treatment. Growth analysis was conducted at bi-weekly intervals during the growing season. In addition, leaf area, leaf dry mass, root dry mass, square dry mass, boll dry mass and total above dry mass per plant were also measured at each sampling. Plant traits, including plant height, number of leaves, number of squares and number of bolls were recorded weekly. The number of days to emergence, squaring, flowering and maturity were also observed. The results showed that by increasing [CO₂] to 600 μmol l^?1 total biomass increased at both temperature levels, but a further increase of [CO₂] up to 800 μmol l^?1 increased total biomass only at the temperature of 35/25 °C. Throughout the growing season, there was no significant effect of [CO₂] levels on LAI. Increasing temperature from 25/15 °C to 35/25 °C had a positive impact on LAI across all CO₂ levels (P < 0.05). Increasing CO₂ from 400 to 600 μmol l^?1 significantly increased the number of squares by 31.4%, but a further increase to 800 μmol l^?1 caused a 6.6% decrease (non-significant) in the number of squares. The interactive effects of [CO₂] and temperature indicated that at a higher temperature, CO₂ would be more beneficial as we proceed towards the end of the growing season. However, further studies are needed to really understand the interaction between higher [CO₂] and temperature levels and cultivar characteristics.     

In vivo temperature limitations of photosynthesis in Phaseolus vulgaris L

The purpose of this study was to evaluate the temperature response of photosynthesis in two common bean genotypes differing in crop yield when grown under warm conditions. The cultivar Nobre is sensitive to high temperatures, whereas Diplomata shows better crop yield under high temperatures. Plants were grown in a greenhouse prior to transferring to a controlled environment cabinet for the temperature treatments. In a first experiment, 30 days-old plants were subjected to a short exposure (1 day) at temperatures that varied from 9 °C to 39 °C. Diplomata had lower net CO₂ assimilation rate (A) at 15 °C and 21 °C, but higher from 27 °C to 39 °C. Photosynthetic parameters calculated from modeling the response of A to the intercellular CO₂ concentration suggested that the different temperature responses of the two genotypes are caused by different rates of diffusion of CO₂ to the assimilation site, not by differences in biochemical limitations of photosynthesis. While stomatal conductance (g_s) did not differ between the genotypes, mesophyll conductance (g_m) was slightly greater for Nobre at 15 °C, but much higher in Diplomata from 21 °C to 39 °C. In a second experiment, no difference was observed in biomass accumulation between the two genotypes after growth for 24 days under a 35/20 °C (day/night) regime. Hence, the differences in photosynthesis did not cause variation in plant growth at the vegetative stage. The differential genotypic response of g_m to temperature suggests that g_m might be an important limitation to photosynthesis in Nobre, the common bean genotype sensitive to elevated temperature. However, more studies are needed employing other methods for g_m evaluation to validate these results.     

Leaf photosynthesis of Haberlea rhodopensis before and during drought

Haberlea rhodopensis is a homoiochlorophyllous resurrection plant that shows a low rate of leaf net CO₂ uptake (4–6 μmol m^?2 s^?1) under saturating photosynthetic photon flux densities in air (21% O₂ and about 390 ppm CO₂). However, leaf net CO₂ uptake reaches values of 17–18 μmol m^?2 s^?1 under saturating CO₂ and light. H. rhodopensis leaves have a very low mesophyll CO₂ conductance that can partly explain the low rate of leaf net CO₂ uptake in normal air. Experimental evidences suggest that mesophyll conductance is not sensitive to temperature in the 20–35 °C range. In addition, it is shown that the (1) transpiration rate of H. rhodopensis is nearly linearly related to the vapour pressure difference between the leaf and the ambient air within the interval from 0.5 kPa to 2.5 kPa at a leaf temperature of 25 °C and (2) leaf net CO₂ uptake in normal air under saturating light does not change much with leaf temperature (between 20 °C and 30 °C). At a leaf relative water content of between 90% and 30%, the decrease of leaf net CO₂ assimilation during drought can be explained by a decrease of leaf CO₂ diffusional conductance. Accordingly the non-photochemical chlorophyll fluorescence quenching decreases only at relative water contents lower than 20%, indicating that photosynthetic activity maintains a trans-thylakoidal proton gradient over a wide range of leaf water contents. Moreover, PSII photochemistry (as estimated by the Fv/Fm ratio and the thermoluminescence B band intensity) is only affected at leaf relative water contents lower than about 20%, thus confirming that primary photosynthetic reactions are resistant to drought. Interestingly, the effect of leaf desiccation on photosynthetic capacity, measured at very high ambient CO₂ molar ratios under saturating PPFD, is identical to that observed for three non-resurrection C₃ mesophytes. This demonstrates that the photosynthetic apparatus of H. rhodopensis is not more resistant to desiccation when compared to other C₃ plants. Since the leaf area decreases by more than 50% when the leaf relative water content is reduced to about 40% during drought it is supposed, following Farrant et al. [Farrant, J.M., Vander, W.C., Lofell, D.A., Bartsch, S., Whittaker, A., 2003. An investigation into the role of light during desiccation of three angiosperms resurrection plants. Plant Cell Environ. 26, 1275–1286], that H. rhodopensis leaf cells avoid mechanical stress.     

Photosynthetic pigments,morphology and leaf gas exchange during ex vitro acclimatization of micropropagated CAM Doritaenopsis plantlets under relative humidity and air temperature

The effect of relative humidity (RH) and temperature on CO₂ assimilation (An), stomatal conductance (Sc), transpiration rate (Tr), chlorophyll content, fresh and dry weight, leaf length, leaf area, leaf width, formation of new root and survival rate have been assayed in Doritaenopsis in growth chamber after 1 month of acclimatization. Reduced growth was observed at below and above 25 °C whereas it was increased with increasing humidity. Relative water content (RWC) was decreased at 50% and 70% humidity after second day of transfer and recovered completely with the progression of acclimatization. RWC also reduced at high temperature but recovered slowly and a gradual decrease of RWC was observed at 15 °C. A visual symptom of severe leaf tip burn was observed at 50–70% humidity and at 35 °C during acclimatization. At 15 °C and 50% humidity sudden decrease of photosynthetic efficiency (F_v/F_m) was observed, which could not recover in temperature treated plantlets during acclimatization period. Chlorophyll content increased with increasing humidity and at 15 and 35 °C chlorophyll content was decreased compared to 25 °C. Chlorophyll a/b ratio was unchanged while total chlorophyll/carotenoids ratio was increased from low to high temperature. Exposure of plantlets to high temperature led to a noticeable decrease in An, Sc and Tr, and at 15 °C they were more decreased whereas significant differences were not observed in the parameters tested under humidity after 25 days of acclimatization. During daytime at 15 °C, increase in An, Sc and Tr indicates the plantlets adaptability in the new environment. The peroxidase activity remained unaffected in all humidity stress whereas low temperature increased the peroxidase activity compared to high temperature. These finding suggests that photosynthetic properties was greatly affected by air temperature conditions with a reduction of An, Sc and Tr at 15 and 35 °C compared to humidity stress that played a greater role in limiting photosynthesis.     

Carbon mineralization of Chinese fir (Cunninghamia lanceolata) soils under different temperature and humidity conditions

Burned and unburned mineral soils (0–10 cm) from a 40-year-old Chinese fir (Cunninghamia lanceolata) forest in Nanping, Fujian, China were incubated for 90 days at different temperatures (25 °C and 35 °C) and humidity [25%, 50%, and 75% of water holding capacity (WHC)] conditions. Carbon (C) mineralization of all soils was determined using CO₂ respiration method. The results showed that CO₂ evolution rates of the burned and control soils exhibited similar temporal patterns, and similar responses to temperature and moisture. CO₂ evolution rates for all soil samples decreased with incubation time. At different humidity conditions, average rate of C mineralization and cumulative mineralized C from burned and control soils were significantly higher at 35 °C than at 25 °C. This implied that C mineralization was less sensitive to soil moisture than to temperature. In both soils at 25 °C or 35 °C, the amount of soil evolved CO₂ over the 90 days incubation increased with increasing moisture content from 25% to 75% WHC. A temperature coefficient (Q₁₀) varied with soil moisture contents. The maximum values recorded for Q₁₀ were 1.7 in control soil and 1.6 in burned soil both at 25% WHC. However, there were no significant differences in Q₁₀ values between the control and burned soils over all moisture ranges (P > 0.05). The data of cumulative C–CO₂ released from control and burned soils were fitted to two different kinetic models. The two simultaneous reactions model described mineralization better than the first-order exponential model, which reflected the heterogeneity of substrate quality. Based on these results, it is possible to conclude that temperature and moisture are important in the controls of C mineralization, and the combined effects of these variables need to be considered to understand and predict the response of CO₂ release in subtropical ecosystems to climate change.     

Effect of high temperature on active oxygen species,senescence and photosynthetic properties in cucumber leaves

To gain a physiological understanding of the effects of high temperatures on cucumber (Cucumis sativus L.), we subjected seedlings to heat treatment at daytime temperatures of 28 °C, 32 °C, and 36 °C for 7 h a day for 30 days. The amount of active oxygen species, indicators of senescence, and photosynthetic properties in the second and third leaves were determined at the start of temperature treatment and on the 15th and 30th days of treatment. The amount of active oxygen species superoxide in leaves was greatest in the high temperature zones on the 15th day of treatment, and the amount of hydrogen peroxide was greatest in the high temperature zones on both the 15th and 30th days of treatment. The reduction in the amount of protein and the increase in the amount of malondialdehyde, both indicators of senescence, were greatest in the high temperature zones on both the 15th and 30th days of treatment, and the amount of chlorophyll was lowest in the 36 °C zone on the 15th day, and lower in the high temperature zones on the 30th day. It is clear from these results that a large amount of active oxygen species is generated and accumulated in the leaves at high temperatures, and senescence is significantly accelerated. The photosynthetic properties of stomatal conductance, sub-stomatal CO₂ concentration, and transpiration rate were at the same level on both the 15th and 30th days of treatment in all three temperature treatment zones. No significant difference was seen in the net photosynthesis rate between the 28 °C and 32 °C zones, was lower in the 36 °C zone than the 32 °C zone on the 15th day, and lowest in the 36 °C zone on the 30th day. CO₂ intake and water absorption are only mildly affected by high temperatures, and the reduction in net photosynthesis rate due to the 36 °C high temperature stress suggests that the large amount of active oxygen species induces inhibition of photosynthesis and damage to the mechanism of photosynthesis.     

Interactive effects of elevated temperature and CO2 levels on metabolism and oxidative stress in two common marine bivalves (Crassostrea virginica and Mercenaria mercenaria)

Marine bivalves such as the hard shell clams Mercenaria mercenaria and eastern oysters Crassostrea virginica are affected by multiple stressors, including fluctuations in temperature and CO₂ levels in estuaries, and these stresses are expected to be exacerbated by ongoing global climate change. Hypercapnia (elevated CO₂ levels) and temperature stress can affect survival, growth and development of marine bivalves, but the cellular mechanisms of these effects are not yet fully understood. In this study, we investigated whether oxidative stress is implicated in cellular responses to elevated temperature and CO₂ levels in marine bivalves. We measured the whole-organism standard metabolic rate (SMR), total antioxidant capacity (TAOC), and levels of oxidative stress biomarkers in the muscle tissues of clams and oysters exposed to different temperatures (22 and 27 °C) and CO₂ levels (the present day conditions of ~ 400 ppm CO₂ and 800 ppm CO₂ predicted by a consensus business-as-usual IPCC emission scenario for the year 2100). SMR was significantly higher and the antioxidant capacity was lower in oysters than in clams. Aerobic metabolism was largely temperature-independent in these two species in the studied temperature range (22–27 °C). However, the combined exposure to elevated temperature and hypercapnia led to elevated SMR in clams indicating elevated costs of basal maintenance. No persistent oxidative stress signal (measured by the levels of protein carbonyls, and protein conjugates with malondialdehyde and 4-hydroxynonenal) was observed during the long-term exposure to moderate warming (+ 5 °C) and hypercapnia (~ 800 ppm CO₂). This indicates that long-term exposure to moderately elevated CO₂ and temperature minimally affects the cellular redox status in these bivalve species and that the earlier observed negative physiological effects of elevated CO₂ and temperature must be explained by other cellular mechanisms.     

Evaluation of structure and hydrolysis activity of Candida rugosa Lip7 in presence of sub-/super-critical CO2

This work aimed to assess the effect of sub-/super-critical CO₂ on the structure and activity of Candida rugosa Lip7 (CRL7) in its solution form. The structure was examined by SDS-PAGE gel electrophoresis, circular dichroism (CD) and fluorescence spectra photometry. Results revealed that the primary structure remained intact after sub-/super-critical CO₂ treatment, and the secondary structure altered at the pressure of 10 MPa and temperature 40 °C for 30 min incubation, but it was reflex to its native form with increasing incubation time up to 150 min under 10 MPa and 40 °C. Meanwhile, the tertiary structure via fluorescence spectra analysis showed that the intensity of the maximal emission wavelength at 338 nm decreased under the conditions of 10 MPa and 40 °C for 150 min. Furthermore, the residue hydrolysis activity and kinetics constants (V_max and K_m) of CRL7 treated with sub-/super-critical CO₂ were also investigated. In cases of 6 MPa and 35 °C, or 10 MPa and 40 °C for 30 min, activity variance of CRL7 was maybe caused by its secondary structure alteration. But in case of 10 MPa and 40 °C for 150 min, the tertiary structure change was perhaps responsibility for CRL7 activity enhancement.     

The role of nest surface temperatures and the brain in influencing ant metabolic rates

Thermal limits of insects can be influenced by recent thermal history: here we used thermolimit respirometry to determine metabolic rate responses and thermal limits of the dominant meat ant, Iridomyrmex purpureus. Firstly, we tested the hypothesis that nest surface temperatures have a pervasive influence on thermal limits. Metabolic rates and activity of freshly field collected individuals were measured continuously while ramping temperatures from 44 °C to 62 °C at 0.25 °C/minute. At all the stages of thermolimit respirometry, metabolic rates were independent of nest surface temperatures, and CT_max did not differ between ants collected from nest with different surface temperatures. Secondly, we tested the effect of brain control on upper thermal limits of meat ants via ant decapitation experiments (‘headedness’). Decapitated ants exhibited similar upper critical temperature (CT_max) results to living ants (Decapitated 50.3±1.2 °C: Living 50.1±1.8 °C). Throughout the temperature ramping process, ‘headedness’ had a significant effect on metabolic rate in total (Decapitated V̇CO₂ 140±30 µl CO₂ mg⁻¹ min⁻¹: Living V̇CO₂ 250±50 CO₂ mg⁻¹ min⁻¹), as well as at temperatures below and above CT_max. At high temperatures (>44 °C) pre- CT_max the relationships between I. purpureus CT_max values and mass specific metabolic rates for living ants exhibited a negative slope whilst decapitated ants exhibited a positive slope. The decapitated ants also had a significantly higher Q₁₀:25–35 °C when compared to living ants (1.91±0.43 vs. 1.29±0.35). Our findings suggest that physiological responses of ants may be able to cope with increasing surface temperatures, as shown by metabolic rates across the thermolimit continuum, making them physiologically resilient to a rapidly changing climate. We also demonstrate that the brain plays a role in respiration, but critical thermal limits are independent of respiration levels.     

Can acclimation of thermal tolerance,in adults and across generations,act as a buffer against climate change in tropical marine ectotherms?

Thermal acclimation capacity was investigated in adults of three tropical marine invertebrates, the subtidal barnacle Striatobalanus amaryllis, the intertidal gastropod Volegalea cochlidium and the intertidal barnacle Amphibalanus amphitrite. To test the relative importance of transgenerational acclimation, the developmental acclimation capacity of A. amphitrite was investigated in F₁ and F₂ generations reared at a subset of the same incubation temperatures. The increase in CT_max (measured through loss of key behavioural metrics) of F₀ adults across the incubation temperature range 25.4–33.4 °C was low: 0.00 °C (V. cochlidium), 0.05 °C (S. amaryllis) and 0.06 °C (A. amphitrite) per 1 °C increase in incubation temperature (the acclimation response ratio; ARR). Although the effect of generation was not significant, across the incubation temperature range of 29.4–33.4 °C, the increase in CT_max in the F₁ (0.30 °C) and F₂ (0.15 °C) generations of A. amphitrite was greater than in the F₀ (0.10 °C). These correspond to ARR's of 0.03 °C (F₀), 0.08 °C (F₁) and 0.04 °C (F₂), respectively. The variability in CT_max between individuals in each treatment was maintained across generations, despite the high mortality of progeny. Further research is required to investigate the potential for transgenerational acclimation to provide an extra buffer for tropical marine species facing climate warming.     

Development response of Spodoptera exigua to eight constant temperatures: Linear and nonlinear modeling

Temperature-dependent development of Spodoptera exigua (Hübner) were evaluated at eight constant temperatures of 12, 15, 20, 25, 30, 33, 34 and 36 °C with a variation of 0.5 °C on sugar beet leaves. No development occurred at 12 °C and 36 °C. Total developmental time varied from 120.50 days at 15 °C to 14.50 days at 33 °C. As temperature increased from 15 °C to 33 °C, developmental rate (1/developmental time) of S. exigua increased but declined at 34 °C. The lower temperature threshold (T_min) was estimated to be 12.98 °C and 12.45 °C, and the thermal constant (K) was 294.99 DD and 311.76 DD, using the traditional and Ikemoto–Takai linear models, respectively. The slopes of the Ikemoto–Takai linear model for different immature stages were different, violating the assumption of rate isomorphy. Data were fitted to three nonlinear models to predict the developmental rate and estimate the critical temperatures. The T_min values estimated by Lactin-2 (12.90 °C) and SSI (13.35 °C) were higher than the value estimated by Briere-2 (8.67 °C). The estimated fastest development temperatures (T_fast) by the Briere-2, Lactin-2 and SSI models for overall immature stages development of S. exigua were 33.4 °C, 33.9 °C and 32.4 °C, respectively. The intrinsic optimum temperature (T_Φ) estimated from the SSI model was 28.5 °C, in which the probability of enzyme being in its native state is maximal. The upper temperature threshold (T_max) values estimated by these three nonlinear models varied from 34.00 °C to 34.69 °C. These findings on thermal requirements can be used to predict the occurrence, number of generations and population dynamics of S. exigua.     

Growth and domoic acid content of Pseudo-nitzschia australis isolated from northwestern Baja California,Mexico, cultured under batch conditions at different temperatures and two Si:NO3 ratios

Domoic acid (DA) poisoning in the southern part of the California Current System has been associated typically with blooms of Pseudo-nitzschia australis. The environmental variables that promote growth and DA production in the Mexican part of this system have not been identified. The present study investigated the effect of temperature and two nutrient ratios on the growth characteristics and DA content of two (BTS-1, BTS-2) P. australis strains isolated from the Pacific coast of northern Baja California peninsula, México. Of the different temperatures assayed (10, 12, 14, 15, 18 and 20 °C), the maximum cell abundance was detected at 12 °C for BTS-2 and 14 °C for BTS-1. The highest maximum specific growth rate (1.69 day⁻¹) was measured at 15 °C for BTS-2. With the exception of cells maintained at 15 °C, growth characteristics were similar in P. australis cultured in a high Si:NO₃ (2.5) or low Si:NO₃ (0.5) ratio at each temperature. Dissolved (dDA) and cellular (cDA) DA content measured at the stationary phase of growth was similar in cells cultivated at the different temperatures. No difference in cDA (between 0.11 and 1.87 pg DA cell⁻¹) was observed in cells cultivated at the two nutrient ratios. To evaluate if P. australis accumulates DA (cDA + dDA) at different stages of the culture and not only during the stationary phase of growth, the BTS-1 strain was cultivated at 14 °C and the content of this toxin was measured during culture development. The cultures were maintained at high (HL; 200 μmol quanta m⁻² s⁻¹) and low light (LL; 30 μmol quanta m⁻² s⁻¹) and in the two nutrient ratios to evaluate the effect of these variables on DA content. The photosynthetic performance and pigment concentration were measured as indicators of the physiological condition of the cells. cDA was detected in all culture conditions and during the different stages of growth. The highest DA content was measured during the lag phase of growth and it was present mainly in the medium (dDA = 70.83 pg DA cell⁻¹). Cells cultivated at HL produced more DA than LL cultured cells. P. australis cultured in HL presented lower photosynthetic rates than LL cells and had similar concentrations of photoprotective pigments and the highest maximum photosynthetic rates were detected during the lag phase of growth in all culture conditions. The results demonstrate that P. australis from northern Baja California peninsula presents a narrow temperature range for optimal growth under batch culture conditions. P. australis produce DA at different stages of growth, and DA content was related to the light intensity at which the cells were cultivated.     

Mixing of oxidized and bilayer phospholipids

Composition and phase dependence of the mixing of 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC), with the oxidized phospholipid, 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine (PGPC) were investigated by characterizing the aggregation states of DPPC/PGPC and DOPC/PGPC using a fluorescence quenching assay, dynamic light scattering, and time-resolved fluorescence quenching in the temperature range 5–60 °C. PGPC forms 3.5 nm radii micelles of aggregation number 33. In the gel phase, DPPC and PGPC fuse to form mixed vesicles for PGPC molar fraction, X_PGPC ≤ 0.3 and coexisting vesicles and micelles at higher X_PGPC. Data suggest that liquid phase DPPC at 50 °C forms mixed vesicles with segregated or hemi fused DPPC and PGPC for X_PGPC ≤ 0.3. At 60 °C, DPPC and PGPC do not mix, but form coexisting vesicles and micelles. DOPC and PGPC do not mix in any proportion in the liquid phase. Two dissimilar aggregates of the sizes of vesicles and PGPC micelles were observed for all X_PGPC for T ≥ 22 °C. DOPC–PGPC and DPPC–PGPC mixing is non-ideal for X_PGPC > 0.3 in both gel and fluid phases resulting in exclusion of PGPC from the bilayer. Formation of mixed vesicles is favored in the gel phase but not in the liquid phase for X_PGPC ≤ 0.3. For X_PGPC ≤ 0.3, aggregation states change progressively from mixed vesicles in the gel phase to component segregated mixed vesicles in the liquid phase close to the chain melting transition temperature to separated coexisting vesicles and micelles at higher temperatures.     

Continuous degradation of maltose by enzyme entrapment technology using calcium alginate beads as a matrix

Maltase from Bacillus licheniformis KIBGE-IB4 was immobilized within calcium alginate beads using entrapment technique. Immobilized maltase showed maximum immobilization yield with 4% sodium alginate and 0.2 M calcium chloride within 90.0 min of curing time. Entrapment increases the enzyme–substrate reaction time and temperature from 5.0 to 10.0 min and 45 °C to 50 °C, respectively as compared to its free counterpart. However, pH optima remained same for maltose hydrolysis. Diffusional limitation of substrate (maltose) caused a declined in V_max of immobilized enzyme from 8411.0 to 4919.0 U ml^?1 min^?1 whereas, K_m apparently increased from 1.71 to 3.17 mM ml^?1. Immobilization also increased the stability of free maltase against a broad temperature range and enzyme retained 45% and 32% activity at 55 °C and 60 °C, respectively after 90.0 min. Immobilized enzyme also exhibited recycling efficiency more than six cycles and retained 17% of its initial activity even after 6th cycles. Immobilized enzyme showed relatively better storage stability at 4 °C and 30 °C after 60.0 days as compared to free enzyme.     

Ecology and evolution of Devonian trees in New York,USA

The first trees in New York were Middle Devonian (earliest Givetian) cladoxyls (?Duisbergia and Wattieza), with shallow-rooted manoxylic trunks. Cladoxyl trees in New York thus postdate their latest Emsian evolution in Spitzbergen. Progymnosperm trees (?Svalbardia and Callixylon–Archaeopteris) appeared in New York later (mid-Givetian) than progymnosperm trees from Spitzbergen (early Givetian). Associated paleosols are evidence that Wattieza formed intertidal to estuarine mangal and Callixylon formed dry riparian woodland. Also from paleosols comes evidence that Wattieza and Callixylon required about 350 mm more mean annual precipitation than plants of equivalent stature today, that Wattieza tolerated mean annual temperature 7 °C less than current limits of mangal (20 °C), and Callixylon could tolerate temperatures 14 °C less than modern mangal. Devonian mangal and riparian woodland spread into New York from wetter regions elsewhere during transient paleoclimatic spikes of very high CO₂ (3923 ± 238 ppmv), and subhumid (mean annual precipitation 730 ± 147 mm) conditions, which were more likely extrinsic atmospheric perturbations rather than consequences of tree evolution. For most of the Middle Devonian CO₂ was lower (2263 ± 238 ppmv), and paleoclimate in New York was semiarid (mean annual precipitation 484 ± 147 mm). Such transient perturbations and immigration events may explain the 40 million year gap between the late Emsian (400 Ma) evolution of trees and Famennian (360 Ma) CO₂ drawdown and expansion of ice caps.     

Estudios de la viabilidad y la vitalidad frente al congelado de la levadura probiótica Saccharomyces boulardii: efecto del preacondicionamiento fisiológico

The aim of this study was to evaluate the vitality and viability of the probiotic yeast Saccharomyces boulardii after freezing/thawing and the physiological preconditioning effect on these properties. The results indicate that the specific growth rate (0.3/h^?1) and biomass (2-3 × 10⁸ cells/ml) of S. boulardii obtained in flasks shaken at 28 °C and at 37 °C were similar. Batch cultures of the yeast in bioreactors using glucose or sugar-cane molasses as carbon sources, reached yields of 0.28 g biomass/g sugar consumed, after 10 h incubation at 28 °C; the same results were obtained in fed batch fermentations. On the other hand, in batch cultures, the vitality of cells recovered during the exponential growth phase was greater than the vitality of cells from the stationary phase of growth. Vitality of cells from fed-batch fermentations was similar to that of stationary growing cells from batch fermentations. Survival to freezing at –20 °C and subsequent thawing of cells from batch cultures was 0.31% for cells in exponential phase of growth and 11.5% for cells in stationary phase. Pre-treatment of this yeast in media with water activity (a_w) 0.98 increased the survival to freezing of S. boulardii cells stored at –20 °C for 2 months by 10 fold. Exposure of the yeast to media of reduced a_w and/or freezing/thawing process negatively affected cell vitality. It was concluded that stress conditions studied herein decrease vitality of S. boulardii. Besides, the yeast strain studied presented good tolerance to bile salts even at low pH values.     

Characterization of a novel thermophilic cyanobacterial strain from Taian hot springs in Taiwan for high CO2 mitigation and C-phycocyanin extraction

The photosynthetic thermophiles have advantage in sequestering CO₂ emitted from the energy sector due to their adaptation to high temperatures, growth at high concentrations of CO₂, and economically important metabolites. The characterization of such a microorganism, a cyanobacterium from Taian hot springs in Taiwan is described here. This thermophilic cyanobacterium is rod-shaped with a size of 1.2–2.5 μm × 6.0–9.0 μm. A comparison of the 16S RNA and cpcBA-IGS sequences revealed that it is closely related to Thermosynechococcus elongatus BP-1 and so named as Thermosynechococcus elongatus TA-1. This cyanobacterium has better growth at 10% and 20% CO₂, at 50 °C with 6000 lx light intensity, at a starting pH of 7–9 and in a medium with 20 mM NaCl. The preferred nitrogen source is NaNO₃ of which the minimal requirement is 10 mM. The purified phycocyanin (C-PC) from TA-1 is still kept native and active at a wide range of temperatures (4–60 °C) with a 65.65% activity even at 60 °C, as well as pH values from 4 to 9 and thus exhibiting a good thermal and acid–base stability. This thermophilic cyanobacterium could make integration of CO₂ mitigation from industrial flue gas and production of economically important product, like C-PC, more feasible.