Influence of Carbon Dioxide and pH on Influenza Virus in Sessile Saliva Droplets.

Traditionally, it has often been hypothesized that cyanobacteria are superior competitors at low CO2 and high pH in comparison with eukaryotic algae, owing to their effective CO2-concentrating mechanism (CCM). However, recent work indicates that green algae can also have a sophisticated CCM tuned to low CO2 levels. Conversely, cyanobacteria with the high-flux bicarbonate uptake system BicA appear well adapted to high inorganic carbon concentrations. To investigate these ideas we studied competition between three species of green algae and a bicA strain of the harmful cyanobacterium Microcystis aeruginosa at low (100 ppm) and high (2000 ppm) CO2. Two of the green algae were competitively superior to the cyanobacterium at low CO2, whereas the cyanobacterium increased its competitive ability with respect to the green algae at high CO2. The experiments were supported by a resource competition model linking the population dynamics of the phytoplankton species with dynamic changes in carbon speciation, pH and light. Our results show (i) that competition between phytoplankton species at different CO2 levels can be predicted from species traits in monoculture, (ii) that green algae can be strong competitors under CO2-depleted conditions, and (iii) that bloom-forming cyanobacteria with high-flux bicarbonate uptake systems will benefit from elevated CO2 concentrations.

Increases in CO2 from past low to future high levels result in “slower” strategies on the leaf economic spectrum

The principal function of isoprene biosynthesis in plants remains unclear, but emission rates are positively correlated with temperature and light, supporting a role for isoprene in maintaining photosynthesis under transient heat and light stress from sunflecks. Isoprene production is also inversely correlated with CO(2) concentrations, implying that rising CO(2) may reduce the functional importance of isoprene. To understand the importance of isoprene in maintaining photosynthesis during sunflecks, we used RNAi technology to suppress isoprene production in poplar seedlings and compared the responses of these transgenic plants to wild-type and empty-vector control plants. We grew isoprene-emitting and non-emitting trees at low (190 ppm) and high (590 ppm) CO(2) concentrations and compared their photosynthetic responses to short, transient periods of high light and temperature, as well as their photosynthetic thermal response at constant light. While there was little difference between emitting and non-emitting plants in their photosynthetic responses to simulated sunflecks at high CO(2), isoprene-emitting trees grown at low CO(2) had significantly greater photosynthetic sunfleck tolerance than non-emitting plants. Net photosynthesis at 42°C was 50% lower in non-emitters than in isoprene-emitting trees at low CO(2), but only 22% lower at high CO(2). Dark respiration rates were significantly higher in non-emitting poplar from low CO(2), but there was no difference between isoprene-emitting and non-emitting lines at high CO(2). We propose that isoprene biosynthesis may have evolved at low CO(2) concentrations, where its physiological effect is greatest, and that rising CO(2) will reduce the functional benefit of isoprene in the near future.

Photosynthetic carbon metabolism was characterized in four photoautotrophic cell suspension cultures. There was no apparent difference between two soybean (Glycine max) and one cotton (Gossypium hirsutum) cell line which required 5% CO(2) for growth, and a unique cotton cell line that grows at ambient CO(2) (660 microliters per liter). Photosynthetic characteristics in all four lines were more like C(3) mesophyll leaf cells than the cell suspension cultures previously studied. The pattern of (14)C-labeling reflected the high ratio of ribulosebisphosphate carboxylase to phosphoenolpyruvate carboxylase activity and showed that CO(2) fixation occurred primarily by the C(3) pathway. Photorespiration occurred at 330 microliters per liter CO(2), 21% O(2) as indicated by the synthesis of high levels of (14)C-labeled glycine and serine in a pulse-chase experiment and by oxygen inhibition of CO(2) fixation. Short-term CO(2) fixation in the presence and absence of carbonic anhydrase showed CO(2), not HCO(3) (-), to be the main source of inorganic carbon taken up by the low CO(2)-requiring cotton cells. The cells did not have a CO(2)-concentrating mechanism as indicated by silicone oil centrifugation experiments. Carbonic anhydrase was absent in the low CO(2)-requiring cotton cells, present in the high CO(2)-requiring soybean cell lines, and absent in other high CO(2) cell lines examined. Thus, the presence of carbonic anhydrase is not an essential requirement for photoautotrophy in cell suspension cultures which grow at either high or low CO(2) concentrations.

Effects of inorganic carbon supply on the nitrogen requirement of two submerged macrophytes, Elodea canadensis and Callitriche cophocarpa

Effects of isosorbide dinitrate (ISDN) on coronary flow and arterial prostaglandin (PG) concentrations were investigated, using dog heart-lung preparations. Two kinds of gases (low and high CO2 gases) were used for the artificial respiration. Low CO2 gas contained 55% O2 and 0.2% CO2, whereas high CO2 gas contained 55% O2 and 8% CO2. Administration of ISDN into a blood reservoir at high CO2 caused an increase in coronary sinus blood flow, which was blocked by indomethacin, but not at low CO2. In the absence of ISDN, the arterial concentration of thromboxane (TX) B2 was larger at high CO2 than at low CO2. ISDN attenuated such an increase in TXB2 concentration caused by CO2. The arterial concentration of 6-keto PGF1 alpha was altered by neither CO2 nor ISDN, but slightly increased with time. Indomethacin lowered the concentrations of 6-keto PGF1 alpha and TXB2. These results suggested that the arterial CO2 tension enhanced the TXA2 synthesis and that ISDN inhibited such a relation between CO2 and TXA2 synthesis. Additionally, the vasodilatory effects of PGI2 was enhanced by elevating the arterial CO2 tension. Thus, the increase in canine coronary flow at high CO2 in the presence of ISDN may be related to the inhibitory effects of ISDN on the TXA2 synthesis enhanced by the high arterial CO2 tension and the facilitatory effects of CO2 on the PGI2-induced vasodilation.

Isosorbide Dinitrate Blocks Thromboxane Synthesis Caused by CO2 in Dog Heart-Lung Preparation

Cotton (Gossypium hirsutum cv. Sicala 34) was grown at 352 ('low CO2') or 710 ('high CO2') µL L-1 atmospheric CO2 in continuously wet soil, or in drying soil, or in drying soil re-wetted after plant wilting. In wet soil, the approximately 15% reduction in transpiration per unit leaf area owing to high CO2 was only half that for other species, whereas effects on growth and leaf area were relatively larger. Consequently, water use per plant was 45-50% higher for high CO2 plants in contrast to other species for which the rate of water use is either the same or lower in high CO2. Greater plant water use early in a drying cycle caused the soil to dry faster under high CO2 than under low CO2. The addition of the consequential greater water stress at high CO2 in drying soil to the direct CO2 effect on stomata caused the transpiration rate of high CO2 plants to fall by up to 60% as the soil dried relative to plants drying at low CO2. After re-wetting the dry soil, the reduction in transpiration rate at high CO2 returned within hours to the value of 15% seen in wet soil. The results were inconsistent with the idea that water deficits increase the sensitivity of stomatal aperture to CO2. Other consequences of drier soil under high CO2 compared with low CO2 were: (a) unlike in many other species, in cotton, the relative growth enhancement by high CO2 is not higher under drying soil compared with wet soil owing to the opposite effect on soil water content; and (b) the increased water-use efficiency in drying soil relative to wet soil was greater in high CO2 plants than in low CO2. The confounding of indirect effects of soil water with the direct CO2 effects may explain the wide variability of literature reports about CO2 effects on stomatal conductance and water use.

Structural basis for C4 photosynthesis without Kranz anatomy in leaves of the submerged freshwater plant Ottelia alismoides.

This study aimed to evaluate the influence of CO2 and temperature on glyphosate-resistant and susceptible biotypes of Amaranthus palmeri (Palmer amaranth) in terms of morphological development. Height (cm), stem diameter (cm), leaf area (cm2), number of leaves, leaf, stem, and root dry matter, plant volume (m3), as well as shoot-to-root allometry were evaluated. The Palmer amaranth biotypes were grown under four different scenarios: 1—low temperature (23/33 °C) and CO2 (410 ± 25 ppm); 2—low temperature (23/33 °C) and high CO2 (750 ± 25 ppm); 3—high temperature (26/36 °C) and low CO2 (410 ± 25 ppm); and 4—high temperature (26/36 °C) and CO2 (750 ± 25 ppm). Between CO2 and temperature, the majority of differences observed were driven by CO2 levels. Palmer amaranth grown under 750 ppm of CO2 was 15.5% taller, displayed 10% more leaf area (cm2), 18% more stem dry matter, and had a 28.4% increase in volume (m3) compared to 410 ppm of CO2. GA2017 and GA2020 were 18% and 15.5% shorter, respectively. The number of leaves was 27% greater for GA2005. Plant volume decreased in GA2017 (35.6%) and GA2020 (23.8%). The shoot-to-root ratio was isomeric, except at 14 and 21 DAT, where an allometric growth towards shoot development was significant. Palmer amaranth biotypes responded differently to elevated CO2, and the impacts of temperature need further investigation on weed physiology. Thus, environmental and genetic background may affect the response of glyphosate-resistant and susceptible populations to climate change scenarios.

The aim of this work was to examine the effect of temperature in the range 5 to 30 ° C upon the regulation of photosynthetic carbon assimilation in leaves of the C4 plant maize (Zea mays L.) and the C3 plant barley (Hordeum vulgare L.). Measurements of the CO2-assimilation rate in relation to the temperature were made at high (735 μbar) and low (143 μbar) intercellular CO2 pressure in barley and in air in maize. The results show that, as the temperature was decreased, (i) in barley, pools of phosphorylated metabolites, particularly hexose-phosphate, ribulose 1,5-bisphosphate and fructose 1,6-bisphosphate, increased in high and low CO2; (ii) in maize, pools of glycerate 3-phosphate, triose-phosphate, pyruvate and phosphoenolpyruvate decreased, reflecting their role in, and dependence on, intercellular transport processes, while pools of hexose-phosphate, ribulose 1,5-bis phosphate and fructose 1,6-bisphosphate remained approximately constant; (iii) the redox state of the primary electron acceptor of photosystem II (QA) increased slightly in barley, but rose abruptly below 12° C in maize. Non-photochemical quenching of chlorophyll fluorescence increased slightly in barley and increased to high values below 20 ° C in maize. The data from barley are consistent with the development of a limitation by phosphate status at low temperatures in high CO2, and indicate an increasing regulatory importance for regeneration of ribulose 1,5-bisphosphate within the Calvin cycle at low temperatures in low CO2. The data from maize do not show that any steps of the C4 cycle are particularly cold-sensitive, but do indicate that a restriction in electron transport occurs at low temperature. In both plants the data indicate that regulation of product synthesis results in the maintenance of pools of Calvin-cycle intermediates at low temperatures.

We grew the amphibious liverwort, Riccia fluitans, at saturating nitrogen and phosphorus concentrations in a cross-factorial design under three levels of light and three levels of CO2 making a matrix of nine treatments. Under these conditions, the relative growth rate (RGR) ranged from 0.011 d−1 at low light and CO2 availability to 0.138 d−1 at high light and CO2 with a significant positive interaction between light and CO2 on the RGR. After the growth experiments, a range of photosynthetic parameters were measured and in particular the maximum net photosynthesis (NPmax) showed a strong acclimation to light and CO2 availability. NPmax decreased significantly with increasing light intensities but increased with increasing CO2 concentration. Surprisingly, no positive correlation between the dark respiration (R) and the RGR was found. Rather, a strong positive correlation between NPmax and R was present and thus a positive correlation between R and RGR cannot be obtained since NPmax and RGR did not develop in parallel with increasing light and CO2 availability. The CO2 compensation point for photosynthesis was also strongly affected by the availability of light and CO2. The CO2 compensation point was very low a high light and low CO2 and increased at low light and high CO2 and there were significant interactions between light and CO2 on the CO2 compensation point throughout the entire experimental matrix. The observed responses to changes in light and CO2 availability and the interactions between the two will alleviate CO2 limitations in dense buoyant mats where the light is typically high. On the other hand, these interactions will also allow penetration to greater depths where light is scarce because the higher CO2 near the bottom can increase the light use efficiency.

Evolutionary adaptation to variation in resource supply has resulted in plant strategies that are based on trade-offs in functional traits. Here, we investigate, for the first time across multiple species, whether such trade-offs are also apparent in growth and morphology responses to past low, current ambient, and future high CO 2 concentrations. We grew freshly germinated seedlings of up to 28 C3 species (16 forbs, 6 woody, and 6 grasses) in climate chambers at 160ppm, 450ppm, and 750ppm CO 2. We determined biomass, allocation, SLA (specific leaf area), LAR (leaf area ratio), and RGR (relative growth rate), thereby doubling the available data on these plant responses to low CO 2. High CO 2 increased RGR by 8%; low CO 2 decreased RGR by 23%. Fast growers at ambient CO 2 had the greatest reduction in RGR at low CO 2 as they lost the benefits of a fast-growth morphology (decoupling of RGR and LAR [leaf area ratio]). Despite these shifts species ranking on biomass and RGR was unaffected by CO 2, winners continued to win, regardless of CO 2. Unlike for other plant resources we found no trade-offs in morphological and growth responses to CO 2 variation, changes in morphological traits were unrelated to changes in growth at low or high CO 2. Thus, changes in physiology may be more important than morphological changes in response to CO 2 variation.

Short-term deprivation effects on smoking-induced heart rate response and smoking behavior were compared in consistently high and low CO absorbing smokers, suggested to depend differentially on smoking and/or nicotine. The subjects came to the laboratory for two afternoon sessions and smoked at 1 p.m. and at 5 p.m. both after previous free smoking and following afternoon or overnight-morning deprivation. Overnight-morning deprivation decreased presmoking heart rate in both groups similarly, but it increased heart rate response to smoking more in the high than low CO absorbers. Single cigarette tidal CO boosts concomitantly decreased in the high CO absorbers and remained at the habitually low level among the low CO absorbers. Afternoon deprivation had no effects on presmoking heart rate, presmoking tidal CO concentration and tidal CO boost, but increased the heart rate response to smoking in the high CO absorbers. Smoking need and satisfaction as well as puff volume and duration tended to increase after both deprivations slightly more among the high than low CO absorbers. These results are discussed in terms of a differential development of acute tolerance to nicotine in the two groups of smokers which dissipates during smoking abstinence periods.

The external inorganic carbon pool (CO(2) + HCO(3) (-)) was measured in both high and low CO(2)-grown cells of Chlamydomonas reinhardtii, using a silicone oil layer centrifugal filtering technique. The average internal pH values were measured for each cell type using [(14)C]dimethyloxazolidinedione, and the internal inorganic carbon pools were recalculated on a free CO(2) basis. These measurements indicated that low CO(2)-grown cells were able to concentrate CO(2) up to 40-fold in relation to the external medium. Low and high CO(2)-grown cells differed in their photosynthetic affinity for external CO(2). These differences could be most readily explained as being due to the relative CO(2)-concentrating capacity of each cell type. This physiological adaptation appeared to be based on changes in the abilities of the cells actively to accumulate inorganic carbon using an energy-dependent transport system.The energy dependence of CO(2) accumulation was investigated, using the inhibitors methyl viologen, 3-(3,4-dichlorophenyl)-1,1 dimethylurea, carbonyl cyanide trifluoromethoxyphenylhydrazone, and 3,5-di-tert-butyl-4-hydroxybenzylide nemalononitrile. It appears that the concentrating mechanism in both cell types may be dependent upon an energy supply linked to both phosphorylation in general and photophosphorylation. The treatment of low CO(2)-grown cells with the carbonic anhydrase inhibitor ethoxyzolamide decreased the apparent photosynthetic affinity for CO(2). This was correlated with a decrease in the transport of inorganic carbon into the cells.The nature of the CO(2)-concentrating mechanism, particularly with respect to a bicarbonate transport system, is discussed, and its possible occurrence in other algae is assessed.