Refixation of xylem sap CO2 in Populus deltoides

Vascular plants have respiring tissues which are perfused by the transpiration stream, allowing solubilization of respiratory CO₂ in the xylem sap. The transpiration stream could provide a conduit for the internal delivery of respiratory CO₂ to leaves. Trees have large amounts of respiring tissues in the root systems and stems, and may have elevated levels of CO₂ in the xylem sap which could be delivered to and refixed by the leaves. Xylem sap from the shoots of three Populus deltoides trees had mean dissolved inorganic carbon concentrations (CO₂+H₂CO₃+HCO^?₃) ranging from 0. 5 to 0. 9 mM. When excised leaves were allowed to transpire 1 mM[¹⁴C]NaHCO₃, 99. 6% of the label was fixed in the light. Seventy-seven percent of the label was fixed in major veins and the remainder was fixed in the minor veins. Autoradiography confirmed that label was confined to the vasculature. In the dark, approximately 80% of the transpired label escaped the leaf, the remainder was fixed in the major veins, slightly elevating dark respiration measurements. This indicates that the vascular tissue in P. deltoides leaves is supplied with a carbon source distinct from the atmospheric source fixed by interveinal lamina. However, the contribution of CO₂ delivered to the leaves in the transpiration stream and fixed in the veins was only 0. 5% of atmospheric CO₂ uptake. In the light 90% of the label was found in sugar, starch and protein, a pattern similar to that found for atmospheric uptake of[¹⁴C]CO₂. Compared with leaves labelled in the light, leaves labelled in the dark had more label in organic acid, amino acid and protein and less label in sugar and starch. After a 5-s pulse the majority of the label fed to petioles in both the light and the dark was found in malate. The majority of the label was found in malate at 120 s in the dark; only 2% of the label was found in phosphorylated compounds at 120 s. The proportion of label found in phosphorylated compounds increased from 17% at 5 s to 80% at 120 s in the light. This suggests that CO₂ delivered to leaves in the light via the transpiration stream is fixed in the veins, a small portion through dark fixation into malate, the remainder by C-3 photosynthesis.     

Chemical speciation of arsenic in urine of patients with blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Although extensive epidemiological study has implicated high arsenic content in artesian well water of the endemic area bears some important connection with the disease, the etiology of the disease is still not clarified. In this study, attention is paid to chemical speciation of arsenic in order to find out whether the concentrations of arsenic species in urine of Blackfoot disease patients are different from those of controls. Experimental results indicate that the total arsenic, inorganic arsenic, monomethylarsonic acid, and other forms of arsenic in the urine of patients are significantly higher than those of the contols. The possible connection of those arsenic species with the etiology of the disease is discussed.     

Effects of methylmercury and inorganic mercury on periphytic diatom communities in freshwater indoor microcosms

The effects of inorganic mercury (HgII) and methylmercury (MeHg) on the colonization of artificial substrates by periphytic diatoms were studied using indoor freshwater microcosms. These consisted of a mixed biotope– water column + natural sediment – with rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea).The periphyton was collected on glass slides in the water column after 34and 71 days. The two Hg sources were introduced either by daily additions to the water column, or once at the beginning into the sediment, using two nominal concentrations: water column, 0.5 μgL^-1 and 2 μg L^-1 for both compounds: sediment, 0.5 mg kg^-1 (fw) and 2 mgkg^-1 (fw) for MeHg and 1 mg kg^-1 (fw) and 10 mgkg^-1 (fw) for HgII. Several complementary criteria were used to analyse the structural and functional perturbations induced: cell density, species richness, diatom size, relative abundance. Exposure to MeHg added to the water column resulted in reduced cell density and changes in species composition with enhancement of e.g. Fallacia pygmaea or Nitzschia palea; inorganic Hg had less effect on the population structure. After contamination via the sediment, the effects of the two compounds were less pronounced than for the water source. This revised version was published online in August 2006 with corrections to the Cover Date.     

SOURCES OF INORGANIC CARBON FOR PHOTOSYNTHESIS BY THREE SPECIES OF MARINE DIATOM1

The utilization of inorganic carbon by three species of marine diatom, Skeletonema costatum (Grev.) Cleve. Ditylum brightwellii (West) Grun., and Chaetoceros calcitrans Paulsen was investigated using an inorganic carbon isotopic disequilibnum technique and inorganic carbon dose-response curves. Stable carbon isotope data of the diatoms are also presented. Observed rates of photosynthetic oxygen evolution were greater than could be accounted for by the theoretical rate of CO₂ supply from the uncatalyzed dehydration of HCO₃^? in the external medium, suggesting use of HCO₃^? as an inorganic carbon source. Data from the isotopic disequilibrium experiment demonstrate the use of both HCO₃^? and CO₂ for photosynthesis. Carbon isotope discrimination values support the use of HCO₃^? by the diatoms.     

Three-step preparation and purification of phosphorus-33-labeled creatine phosphate of high specific activity

Rabbit heart mitochondria were used as a source of enzymes for the synthesis of phosphoruslabeled creatine phosphate. This method is based on the coupled reaction between mitochondrial oxidative phosphorylation and mitochondrial-bound creatine kinase. It is possible to convert more than 90% of the inorganic phosphate (P_i) to creatine phosphate. The method used only small amounts of adenine nucleotides which led to a product with only slight nucleotide contamination. This could be removed by activated charcoal extraction. For further purification, a method for the removal of residual P_i is described.     

Pyrophosphate functions as phosphoryl donor with UDP-glucose-treated mammalian phosphofructokinase

CGP 28392, a novel compound structurally related to the dihydropyridine Ca2+-entry blockers, causes a dose-dependent increase in intracellular free Ca2+ in human platelets, as measured with the Quin-2 Ca2+ indicator, with a semimaximal effective concentration of 2.2 X 10(-7) M. This effect occurs in a concentration range in which CGP 28392 competes for specific [3H]nitrendipine binding in guinea pig heart membranes. It can be inhibited by nitrendipine. The data presented furnish direct evidence of the Ca2+-entry-stimulating properties of CGP 28392 and indicate the presence of dihydropyridine-susceptible structures in human platelets.     

Effects of light quality,CO2 tensions and NO 3 +− concentrations on the inorganic nitrogen metabolism of Chlamydomonas reinhardii

The blue light dependent utilization of nitrate by green algae under common air and high irradiances, besides its assimilatory nature, is associated with the release of NO₂ ^– and NH₄ ⁺ to the culture medium. If the CO₂ content of the sparging air was increased up to 2%, previously excreted NO₂ ^– and NH₄ ⁺ were rapidly assimilated. When under air and high irradiances the cell density in the culture reached values corresponding to 25 g Ch 1.ml^-1, no further growth was observed and the highest values of NO₃ ^– consumption and NO₂ ^– and NH₄ ⁺ release were attained. Besides low CO₂ tensions, increasing NO₃ ^– concentrations in the medium stimulated the release of NO₃ ^– and NH₄ ⁺. Under CO₂-free air the consumption of NO₃ ^– and the release of NO₂ ^– and NH₄ ⁺ on a total N bases were almost stoichiometric and their rates saturated at much lower irradiances than under air. Under CO₂-free air high rates of NO₂ ^– release were only observed under the blue radiations that were effectively absorbed by photosynthetically active pigments, i.e. 460 nm, but not under 404 and 630 nm radiations. However, the simultaneous illumination of the cells with 404 and 630 nm monochromatic light showed a remarkable synergistic effect on NO₂ ^– release.The results are discussed in terms of the close relationship between C and N metabolism, the photosynthetic reducing power required to convert NO _inf3 ^sup± -N into R – NH₂-N and the blue light activation of nitrate reductase.     

Measurement of the inorganic pyrophosphate in tissues of Pisum sativum L.

Purified pyrophosphate: fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90) was used to measure the inorganic pyrophosphate in unfractionated extracts of tissues of Pisum sativum L. The fructose 1,6-bisphosphate produced by the above enzyme was measured by coupling to NADH oxidation via aldolase (EC 4.1.2.13), triosephosphate isomerase (EC 5.3.1.1) and glycerol-3-phosphate dehydrogenase (EC 1.1.1.8). Amounts of pyrophosphate as low as 1 nmol could be measured. The contents of pyrophosphate in the developing embryo of pea, and in the apical 2 cm of the roots, were appreciable; 9.4 and 8.9 nmol g^-1 fresh weight, respectively. The possibility that pyrophosphate acts in vivo as an energy source for pyrophosphate: fructose 6-phosphate 1-phosphotransferase and for UDPglucose pyrophosphorylase (EC 2.7.7.9) is considered.     

Effect of plant growth and addition of plant residues on the phosphatase activity in soil

Summary The phosphatase activity of the soil amended with roots and tops of clover (Trifolium repens) plant material (0.1% by weight) remained essentially constant in the absence of growing plants but changed considerably in the presence of plants (Avena sativa) grown for 10 weeks. There was a significant relationship between the phosphatase activity and organic and inorganic P in the soil solution only in the presence of growing plants. The differences in phosphatase activity between roots and tops amended soil were attributed to total C as well as differences in the degree of availability of C added through plant materials. This may also apply to the carpet grass (Axonopus affinis) amended soil.