A pyrenoid-based carbon-concentrating mechanism is present in terrestrial bryophytes of the class Anthocerotae

It has been widely accepted that carbon assimilation in bryophytes is exclusively based on the conventional C₃ photosynthetic pathway. The occurrence of biochemical CO₂-concentrating mechanisms (C₄ or Crassulacean acid metabolism), which have developed in plants in the last 20–100 million years, has been discounted for bryophytes from studies of the carbon isotope composition (¹³C) of organic material. In contrast cyanobacteria and many algae show active accumulation of dissolved inorganic carbon via biophysical CO₂-concentrating mechanisms which are also found in the photobiont partners in certain lichens. The presence of a pyrenoid, a granular particle within the chloroplast, has been linked with CO₂-concentrating mechanism activity in green algae and lichens and we now show that such a mechanism is categorically associated with the occurrence of a pyrenoid in bryophytes belonging to the class of Anthocerotae. These observations have significant evolutionary implications for the development of terrestrial photosynthesis during the colonisation of the land, raising the intriguing question of why the pyrenoid-based CO₂-concentrating mechanism did not persist in the terrestrial environment.Abbreviations and Symbols CCM carbon-concentrating mechanism - DIG dissolved inorganic carbon (CO₂+HCO ₃ ^- +CO ₂ ^- ) - DW dry weight - K_0.5 external concentration of CO₂ at which half-maximal rates of CO₂ assimilation are reached - Rubisco ribulose-l,5-bisphosphate carboxylase-oxygenase - carbon isotope discrimination (%) - ¹³C carbon isotope ratio (%) This work was supported by the Natural Environment Research Council (GR3/8813) and the Leverhulme Trust. We thank Prof. A. Roy Perry (National Museum of Wales, Cardiff), Dr. B. Coppins and Mr. D. Long (Royal Botanic Garden Edinburgh) for access to herbarium specimens and Mr. M. Fletcher for providing living bryophytes.     

Contribution of Monsoon Asia to the carbon budget of the biosphere,past and future

The High Resolution Biosphere Model (HRBM), which has been developed by the group of the author, was used to investigate the carbon balance of the vegetation and the soil in the ecosystems of Monsoon Asia in comparison to the rest of the world. The HRBM is a global grid-based (0.5 degree resolution) model with a monthly time step. It includes modules for natural vegetation, land use, vegetation fires, vegetation composition. A historical carbon budget was calculated for the period 1860–1978 and, on a global scale, validated using atmospheric CO₂ data. Based on the per-country development of the population and their requirements, different reasonable scenarios were used to investigate the potential impacts of land use and deforestation in the period 1990–2050. The HRBM calculates considerable contributions of Monsoon Asia to the global CO₂ emissions due to land use changes in the past. Between 1860 and 1978, about 1/4 of the global releases from land use changes came from South Asian and Southeast Asian biota. The future contributions in the period 1990–2050 depend on the assumed development of the agricultural methods. If the intensity of agriculture and the agricultural productivity will stay the same as in the 1980s, there will be a strong need to increase agricultural areas, and thus deforestation will dominate. If there will be a change over to intensive methods of agricultural production, the presently used areas might be sufficient to provide resources to the growing population.     

生长光强对亚热带自然林两种木本植物稳定碳同位素比、细胞间CO2浓度和水分利用效率的影响

生长于１００％、４０％和１６％自然光下的荷木和黧蒴幼苗叶片稳定碳同位素比（δ１３Ｃ,－‰）,细胞间ＣＯ２浓度（Ｃｉ）和水分利用效率（ＷＵＥ）有一定的差别。１６％和４０％弱光下,δ１３Ｃ的负值增加－０．５４Ｊ‰到－０．８９‰。Ｃｉ增大８．１－１３．２μｉＬ－１,ＷＵＥ则下降６－２４％。结果表明,叶片的水分和气体交换特性受生长光强的调节,叶片的δ１３Ｃ值可反映其生长过程中受光的强弱状况。     

Age-related differences in TGF-α and proto-oncogenes expression in rat liver after a low dose of carbon tetrachloride

The resiliency of rats during early postnatal development to CCl₄ or to an interactive hepatotoxicity of chlordecone (CD) + CCl₄ has been shown to be due to an efficient stimulation of tissue repair. The objective of the current study was to investigate if this is due to efficient expression of transforming growth factor-α (TGF-α) and proto-oncogenes. Postnatally developing (20 day old) and adult (60 day old) male Sprague–Dawley rats were challenged with a single low dose of CCl₄ (100 μL/kg, ip) or corn oil. Liver samples were collected during a time course (0–96 h) after the administration of CCl₄ and used to examine TGF-α and early (c-fos) and late (H-ras and K-ras) proto-oncogenes mRNA expressions. Significant increases in TGF-α, H-ras, and K-ras gene expressions were evident as early as 12 hours after CCl₄ and peaked between 24 and 48 hours in an age-dependent manner as detected by slot-blot analysis. Results of the study revealed three- and twofold increases in TGF-α gene expression in 20 and 60 day old rats, respectively, after CCl₄. There were 3.5- and 2.5-fold increases in H-ras and 4.4- and 3.4-fold increases in K-ras in 20 and 60 day old rats, respectively. In contrast, a 10-fold increase in c-fos mRNA expression was evident in 20 day old rats 1 hour after CCl₄ treatment, returning to the baseline value by 3 hours, whereas in 60 day old rats, this increase was less than twofold. The overall findings of this study indicate that TGF-α and the early and late proto-oncogene mRNA expressions were enhanced in an age- and time-dependent manner in response to a low dose of CCl₄. These results further strengthen the view that the remarkable resiliency of rats to hepatotoxicants during early postnatal development is due to substantial increases in stimulation of hepatocellular regeneration and tissue repair mechanisms, leading to regression of liver injury and recovery. © 1996 John Wiley & Sons, Inc.     

Mechanism of dissimilatory sulfite reduction by Desulfovibrio desulfuricans: purification of a membrane-bound sulfite reductase and coupling iwth cytochrome c 3 and hydrogenase

The localization of the dissimilatory sulfite reductase in Desulfovibrio desulfuricans strain Essex 6 was investigated. After treatment of the cells with lysozyme, 90% of the sulfite reductase activity was found in the membrane fraction, compared to 30% after cell rupture with the French press. Sulfite reductase was purified from the membrane (mSiR) and the soluble (sSiR) fractiion. On SDS-PAGE, both mSiR and sSiR exhibited three bands at 50, 45 and 11 kDa, respectively. From their UV/VIS properties (distinct absorption maxima at 391, 410, 583, 630 nm, enzymes as isolated) and the characteristic red fluorescence in alkaline solution, mSiR and sSiR were identified as desulfoviridin. Sulfite reductase (HSO₃ ^-H₂S) activity was reconstituted by coupling of mSiR to hydrogenase and cytochrome c ₃ from D. desulfuricans. The specific activity of mSiR was 103 nmol H₂ min^-1 mg^-1, and sulfide was the major product (72% of theoretical yield). No coupling was found with sSiR under these conditions. Furthermore, carbon monoxide was used to diferentiate between the membrane-bound and the soluble sulfite reductase. In a colorimetric assay, with photochemically reduced methyl viologen as redox mediator, CO stimulated the activity of sSiR significantly. CO had no effect in the case of mSiR. These studies documented that, as isolated, both forms of sulfite reductase behaved differently in vitro. Clearly, in D. desulfuricans, the six electron conversion HSO₃ ^-H₂S was achieved by a membranebound desulfoviridin without the assistance of artificial redox mediators, such as methyl viologen.Abbreviations SiR sulfite reductase - mSiR sulfite reductase purified from membranes - sSiR sulfite reductase purified from the soluble fraction Enzymes Sulfite reductase, EC 1.8.99.1 Cytochrome c ₃ hydrogenase, EC 1.12.2.1     

Desulfurization of dibenzothiophene to 2-hydroxybiphenyl by some newly isolated bacterial strains

Gram-positive, non-spore-forming, non-acid-fast, rod-shaped aerobic bacteria with the ability to desulfurize dibenzothiophene (DBT) or dibenzosulfone (DBTO₂) were isolated from soil samples contaminated with fossil fuels. Using a bioavailability method, cells with the desired DbtS⁺ phenotype were enriched. Modified fluorescence and colorimetric assays were used for the initial detection of 2-hydroxybiphenyl (OH-BP) in microtiter plates; subsequently, isolates were grown in wells of microtiter plates and screened for the production of desulfurization product. Fluorescence under UV light and the production of colored product in the phenol assay were used as presumptive indications of production of OH-BP. Confirmation of the presence of OH-BP was achieved with HPLC, UV-absorbance, and mass spectrometry. Nutrient utilization and fatty acid composition (as discerned with Biolog plates and gas chromatography, respectively) were used to identify presumptively the strains as Rhodococcus erythropolis; colony and cell morphology may not be consistent with the identification achieved by nutrient utilization and fatty acid composition. The desulfurization end product, OH-BP, can not be used as carbon source by the tested strain, N1-36.     

Relationships between biovolume and carbon and nitrogen content of bacterioplankton

Abstract Cell volume, carbon and nitrogen content were determined for bacteria grown in batch cultures in water samples collected at five localities in western Florida, USA. Cultures were set up by inoculating 0.2 μm filtered water with 2.5 to 7.0% of 1.0 μm filtered water. Biovolumes of the bacteria were measured by epifluorescence photomicrography. Bacterial carbon and nitrogen contents were determined with a CHN analyser. During incubations, bacterial volumes doubled from 0.070±0.037 μ m³(mean ± S.E.) to 0.153 ± 0.036 μ m³ at early stationary phase. Bacterial C:N ratios ranged between 2.8 and 10.3, with a mean of 6.5, and were inversely correlated with cell volumes. Conversion factors for volume to carbon and nitrogen content were relatively high and variable, ranging from 0.21 to 161 pg C μm⁻³ (mean: 0.72 pg C μm⁻³) and from 0.05 to 0.25 pg N μm⁻³ (mean: 0.12 pg N μm⁻³). Small cells contained more C and N per unit volume than did large cells. The data suggested that biovolume to biomass conversion factors may be higher than previously thought and may be highly variable both temporally and geographically.     

Woody-tissue respiration for Simarouba amara and Minquartia guianensis,two tropical wet forest trees with different growth habits

We measured CO₂ efflux from stems of two tropical wet forest trees, both found in the canopy, but with very different growth habits. The species were Simarouba amara, a fast-growing species associated with gaps in old-growth forest and abundant in secondary forest, and Minquartia guianensis, a slow-growing species tolerant of low-light conditions in old-growth forest. Per unit of bole surface, CO₂ efflux averaged 1.24 mol m^–2 s^–1 for Simarouba and 0.83 mol m^–2s^–1 for Minquartia. CO₂ efflux was highly correlated with annual wood production (r ²=0.65), but only weakly correlated with stem diameter (r ²=0.22). We also partitioned the CO₂ efflux into the functional components of construction and maintenance respiration. Construction respiration was estimated from annual stem dry matter production and maintenance respiration by subtracting construction respiration from the instantaneous CO₂ flux. Estimated maintenance respiration was linearly related to sapwood volume (39.6 mol m^–3s^–1 at 24.6° C, r ²=0.58), with no difference in the rate for the two species. Maintenance respiration per unit of sapwood volume for these tropical wet forest trees was roughly twice that of temperate conifers. A model combining construction and maintenance respiration estimated CO₂ very well for these species (r ²=0.85). For our sample, maintenance respiration was 54% of the total CO₂ efflux for Simarouba and 82% for Minquartia. For our sample, sapwood volume averaged 23% of stem volume when weighted by tree size, or 40% with no size weighting. Using these fractions, and a published estimate of aboveground dry-matter production, we estimate the annual cost of woody tissue respiration for primary forest at La Selva to be 220 or 350 g C m^–2 year^–1, depending on the assumed sapwood volume. These costs are estimated to be less than 13% of the gross production for the forest.