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1.
A molecular approach to drought-induced reduction in leaf CO2 exchange in drought-resistant Quercus ilex.
Rodríguez-Calcerrada, J, Rodrigues, AM, Perdiguero, P, António, C, Atkin, OK, Li, M, Collada, C, Gil, L
Physiologia plantarum. 2018;(4):394-408
Abstract
Drought-induced reduction of leaf gas exchange entails a complex regulation of the plant leaf metabolism. We used a combined molecular and physiological approach to understand leaf photosynthetic and respiratory responses of 2-year-old Quercus ilex seedlings to drought. Mild drought stress resulted in glucose accumulation while net photosynthetic CO2 uptake (Pn ) remained unchanged, suggesting a role of glucose in stress signaling and/or osmoregulation. Simple sugars and sugar alcohols increased throughout moderate-to-very severe drought stress conditions, in parallel to a progressive decline in Pn and the quantum efficiency of photosystem II; by contrast, minor changes occurred in respiration rates until drought stress was very severe. At very severe drought stress, 2-oxoglutarate dehydrogenase complex gene expression significantly decreased, and the abundance of most amino acids dramatically increased, especially that of proline and γ-aminobutyric acid (GABA) suggesting enhanced protection against oxidative damage and a reorganization of the tricarboxylic cycle acid cycle via the GABA shunt. Altogether, our results point to Q. ilex drought tolerance being linked to signaling and osmoregulation by hexoses during early stages of drought stress, and enhanced protection against oxidative damage by polyols and amino acids under severe drought stress.
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Does Aerobic Respiration Produce Carbon Dioxide or Hydrogen Ion and Bicarbonate?
Swenson, ER
Anesthesiology. 2018;(5):873-879
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Abstract
Maintenance of intracellular pH is critical for clinical homeostasis. The metabolism of glucose, fatty acids, and amino acids yielding the generation of adenosine triphosphate in the mitochondria is accompanied by the production of acid in the Krebs cycle. Both the nature of this acidosis and the mechanism of its disposal have been argued by two investigators with a long-abiding interest in acid-base physiology. They offer different interpretations and views of the molecular mechanism of this intracellular pH regulation during normal metabolism. Dr. John Severinghaus has posited that hydrogen ion and bicarbonate are the direct end products in the Krebs cycle. In the late 1960s, he showed in brain and brain homogenate experiments that acetazolamide, a carbonic anhydrase inhibitor, reduces intracellular pH. This led him to conclude that hydrogen ion and bicarbonate are the end products, and the role of intracellular carbonic anhydrase is to rapidly generate diffusible carbon dioxide to minimize acidosis. Dr. Erik Swenson posits that carbon dioxide is a direct end product in the Krebs cycle, a more widely accepted view, and that acetazolamide prevents rapid intracellular bicarbonate formation, which can then codiffuse with carbon dioxide to the cell surface and there be reconverted for exit from the cell. Loss of this "facilitated diffusion of carbon dioxide" leads to intracellular acidosis as the still appreciable uncatalyzed rate of carbon dioxide hydration generates more protons. This review summarizes the available evidence and determines that resolution of this question will require more sophisticated measurements of intracellular pH with faster temporal resolution.
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The impact of environmental factors on carbon dioxide fixation by microalgae.
Morales, M, Sánchez, L, Revah, S
FEMS microbiology letters. 2018;(3)
Abstract
Microalgae are among the most productive biological systems for converting sunlight into chemical energy, which is used to capture and transform inorganic carbon into biomass. The efficiency of carbon dioxide capture depends on the cultivation system configuration (photobioreactors or open systems) and can vary according to the state of the algal physiology, the chemical composition of the nutrient medium, and environmental factors such as irradiance, temperature and pH. This mini-review is focused on some of the most important environmental factors determining photosynthetic activity, carbon dioxide biofixation, cell growth rate and biomass productivity by microalgae. These include carbon dioxide and O2 concentrations, light intensity, cultivation temperature and nutrients. Finally, a review of the operation of microalgal cultivation systems outdoors is presented as an example of the impact of environmental conditions on biomass productivity and carbon dioxide fixation.
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Estimating CO2 gas exchange in mixed age vegetable plant communities grown on soil-like substrates for life support systems.
Velichko, VV, Tikhomirov, AA, Ushakova, SA
Life sciences in space research. 2018;:47-51
Abstract
If soil-like substrate (SLS) is to be used in human life support systems with a high degree of mass closure, the rate of its gas exchange as a compartment for mineralization of plant biomass should be understood. The purpose of this study was to compare variations in CO2 gas exchange of vegetable plant communities grown on the soil-like substrate using a number of plant age groups, which determined the so-called conveyor interval. Two experimental plant communities were grown as plant conveyors with different conveyor intervals. The first plant community consisted of conveyors with intervals of 7 days for carrot and beet and 14 days for chufa sedge. The conveyor intervals in the second plant community were 14 days for carrot and beet and 28 days for chufa sedge. This study showed that increasing the number of age groups in the conveyor and, thus, increasing the frequency of adding plant waste to the SLS, decreased the range of variations in CO2 concentration in the "plant-soil-like substrate" system. However, the resultant CO2 gas exchange was shifted towards CO2 release to the atmosphere of the plant community with short conveyor intervals. The duration of the conveyor interval did not significantly affect productivity and mineral composition of plants grown on the SLS.
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5.
Crop quality under rising atmospheric CO2.
Uddling, J, Broberg, MC, Feng, Z, Pleijel, H
Current opinion in plant biology. 2018;(Pt B):262-267
Abstract
Crops grown under elevated CO2 (eCO2) typically exhibit enhanced yields but at the same time decreased nutritional quality. The latter effect has often been explained as a growth dilution phenomenon, but this cannot be the only process involved since crop nutrient concentrations are decreased also when production is unaffected by eCO2. We review the current knowledge on eCO2 effects on crop nutritional quality with focus on the current understanding of the possible mechanisms and processes causing these effects. Emphasis is on crop nitrogen (N) and protein concentrations but effects on other nutrients and how they compare with those on N are also covered.
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Elevated CO2 reduces the adverse effects of drought stress on a high-yielding soybean (Glycine max (L.) Merr.) cultivar by increasing water use efficiency.
Wang, A, Lam, SK, Hao, X, Li, FY, Zong, Y, Wang, H, Li, P
Plant physiology and biochemistry : PPB. 2018;:660-665
Abstract
Soybean (Glycine max (L.) Merr.) is the world's most important grain legume. The impacts of climate change such as elevated CO2 and drought on soybean physiological and morphological responses are not well understood. This study evaluated the effects of elevated CO2 (ambient concentration + 200 mmol mol-1) and drought stress (35-45% of relative water content) on soybean leaf photosynthesis, chlorophyll fluorescence, stress physiological indexes, morphological parameters, biomass and yield over 2 years at the open-top chamber (OTC) experimental facility in North China. We found that drought decreased intrinsic efficiency of PSII (Fv'/Fm'), effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching coefficient (qP), and yield of soybean, increased nonphotochemical quenching (NPQ), peroxidase (POD), and malondialdehyde (MDA), but had no effect on superoxide dismutase (SOD) or soluble sugar content. Elevated [CO2] increased net photosynthetic rate (PN), water-use efficiency (WUE), ΦPSII, qP, SOD, soluble sugar content and yield of soybean. Elevated [CO2] enhanced the positive effects of drought on WUE, but reduced the negative effects of drought on ΦPSII and qP. Elevated [CO2] enhanced the resistance to drought by improving the capacity of photosynthesis and WUE in soybean leaves.
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[Effects of elevated CO2 concentration on production and water use efficiency of spring wheat in semi-arid area].
Zhang, K, Wang, RY, Li, QZ, Wang, HL, Zhao, H, Yang, FL, Zhao, FN, Qi, Y
Ying yong sheng tai xue bao = The journal of applied ecology. 2018;(9):2959-2969
Abstract
In the present study, the response of spring wheat production and water use efficiency (WUE) to the elevated CO2 concentrations was investigated based on the open-top chamber (OTC) experiment platform in Dingxi, a typical semi-arid area. Three different CO2 concentrations (390 μmol·mol-1, 480 μmol·mol-1 and 570 μmol·mol-1) were involved. The results showed that the air temperature above plant canopy increased and the soil temperature at depth of 10 cm decreased by elevated CO2. The increased CO2 concentration substantially enhanced the total and each component biomass. The aboveground dry mass under the increased CO2 concentrations (480 and 570 μmol·mol-1) was increased by 20.6% and 41.5%, respectively, and the total dry mass was increased by 19.3% and 39.6%, respectively. The biomass enhacement was mainly due to the increases of dry mass of stems and leaves, which was strongly related to the material production capacity during the middle growth stage. The root/shoot ratio under the increased CO2 concentrations (480 and 570 μmol·mol-1) was decreased by 7.3% and 11.8%, respectively, indicating that the elevated CO2 affected the dry matter accumulation of aboveground more than that of belowground. The yields of spring wheat under the increased CO2 concentrations (480 and 570 μmol·mol-1) were higher than that of the control by 8.9% and 19.9%, respectively, mainly due to the increase of grains per spike. The long-term effect of elevated CO2 concentration on the photosynthesis of spring wheat was not obvious. The photosynthetic rate significantly increased, the transpiration rate decreased and the evapotranspiration reduced with the increases of CO2 concentration. WUE at the leaf, population, and yield levels increased under elevated CO2 concentration, with the increase range of WUE being the largest at the population level and the lowest at the yield level.
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Night-time transpiration in barley (Hordeum vulgare) facilitates respiratory carbon dioxide release and is regulated during salt stress.
Even, M, Sabo, M, Meng, D, Kreszies, T, Schreiber, L, Fricke, W
Annals of botany. 2018;(4):569-582
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Abstract
BACKGROUND AND AIMS Night-time transpiration accounts for a considerable amount of water loss in crop plants. Despite this, there remain many questions concerning night-time transpiration - its biological function, regulation and response to stresses such as salinity. The aim of the present study was to address these questions on 14- to 18-d-old, hydroponically grown barley plants. METHODS Plants were either stressed for the last 4-7 d prior to, and during subsequent continuous (24 h), diurnal gravimetric transpiration analyses; or subjected to salt stress just before analyses; or stressed for 4-7 d and then transferred to control medium before analyses. The idea behind this experimental setup was to distinguish between a longer- (cuticle, stomata) and shorter-term (stomata) response of transpiration to treatments. Cuticular conductance was assessed through residual transpiration measurements in detached leaves. Cuticle wax load and dark respiration rate of leaves were determined. Leaf conductance to CO2 was calculated. KEY RESULTS Night-time and daytime transpiration rates were highly, and positively, correlated with each other, across all treatments. Night-time transpiration rates accounted for 9-17 % of daytime rates (average: 13.8 %). Despite minor changes in the ratio of night- to daytime transpiration rates, the contribution of cuticular and stomatal conductance to leaf (epidermal) conductance to water vapour differed considerably between treatments. Salt stress did not affect cuticle wax load. The conductance for CO2 of the cuticle was insufficient to support rates of dark respiratory CO2 release. CONCLUSIONS The main biological function of night-time transpiration is the release of respiratory CO2 from leaves. Night-time transpiration is regulated in the short and long term, also under salt stress. Stomata play a key role in this process. We propose to refer, in analogy to water use efficiency (WUE) during the day, to a CO2 release efficiency ('CORE') during the night.
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The effect of L-rhamnose on intestinal transit time, short chain fatty acids and appetite regulation: a pilot human study using combined 13CO2/H2 breath tests.
Byrne, CS, Preston, T, Brignardello, J, Garcia-Perez, I, Holmes, E, Frost, GS, Morrison, DJ
Journal of breath research. 2018;(4):046006
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Abstract
BACKGROUND The appetite-regulating effects of non-digestible carbohydrates (NDC) have in part previously been attributed to their effects on intestinal transit rates as well as microbial production of short chain fatty acids (SCFA). Increased colonic production of the SCFA propionate has been shown to reduce energy intake and stimulate gut hormone secretion acutely in humans. OBJECTIVE We investigated the effect of the propiogenic NDC, L-rhamnose, on gastrointestinal transit times using a combined 13CO2/H2 breath test. We hypothesised that L-rhamnose would increase plasma propionate leading to a reduction in appetite, independent of changes in gastrointestinal transit times. DESIGN We used a dual 13C-octanoic acid/lactose 13C-ureide breath test combined with breath H2 to measure intestinal transit times following the consumption of 25 g d-1 L-rhamnose, compared with inulin and cellulose, in 10 healthy humans in a randomised cross-over design pilot study. Gastric emptying (GE) and oro-caecal transit times (OCTTs) were derived from the breath 13C data and compared with breath H2. Plasma SCFA and peptide YY (PYY) were also measured alongside subjective measures of appetite. RESULTS L-rhamnose significantly slowed GE rates (by 19.5 min) but there was no difference in OCTT between treatments. However, breath H2 indicated fermentation of L-rhamnose before it reached the caecum. OCTT was highly correlated with breath H2 for inulin but not for L-rhamnose or cellulose. L-rhamnose consumption significantly increased plasma propionate and PYY but did not significantly reduce subjective appetite measures. CONCLUSIONS The NDCs tested had a minimal effect on intestinal transit time. Our data suggest that L-rhamnose is partially fermented in the small intestine and that breath H2 reflects the site of gastrointestinal fermentation and is only a reliable marker of OCTT for certain NDCs (e.g. inulin). Future studies should focus on investigating the appetite-suppressing potential of L-rhamnose and verifying the findings in a larger cohort.
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Linked cycles of oxidative decarboxylation of glyoxylate as protometabolic analogs of the citric acid cycle.
Springsteen, G, Yerabolu, JR, Nelson, J, Rhea, CJ, Krishnamurthy, R
Nature communications. 2018;(1):91
Abstract
The development of metabolic approaches towards understanding the origins of life, which have focused mainly on the citric acid (TCA) cycle, have languished-primarily due to a lack of experimentally demonstrable and sustainable cycle(s) of reactions. We show here the existence of a protometabolic analog of the TCA involving two linked cycles, which convert glyoxylate into CO2 and produce aspartic acid in the presence of ammonia. The reactions proceed from either pyruvate, oxaloacetate or malonate in the presence of glyoxylate as the carbon source and hydrogen peroxide as the oxidant under neutral aqueous conditions and at mild temperatures. The reaction pathway demonstrates turnover under controlled conditions. These results indicate that simpler versions of metabolic cycles could have emerged under potential prebiotic conditions, laying the foundation for the appearance of more sophisticated metabolic pathways once control by (polymeric) catalysts became available.