The effect of air containing O2 −,O2 +, CO2 − and CO2 + on the growth of seedlings ofHordeum Vulgaris

Equipment was devised which permitted the addition of specific gaseous ions to the atmosphere of plastic chambers in which seedlings of HORDEUM VULGARIS were grown in sand culture supplied with chemically defined nutrient solutions. Moderate densities of O₂ ^– or O₂ ⁺ ions (1.8×10⁴/cm³)in air containing an added 8% of O₂ accelerated the growth rate. A like number of CO₂ ^– or CO₂ ⁺ ions in air containing 8% of CO₂ inhibited growth, impeded the production of chlorophyll and devitalized the young seedlings. Evidence is presented that O₂ ^– and O₂ ⁺ stimulate the production of cytochromes and other Fe-containing enzymes through their action on the plant regulatory system responsible for the control of Fe metabolism. The toxic effect of CO₂ ^– and CO₂ ⁺ cannot be explained as yet.

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Zusammenfassung Eine Apparatur wurde entwickelt, die die Zufuhr von ionisiertem Gas der AtmosphÄre in Kammern gestattet. Darin wurden Keimlinge von HORDEUM VULGARIS in Sand mit chemisch definierten NÄhrlösungen gezüchtet. Konzentrationen von 1,8×10⁴/cm³ O₂ ^– und O₂ ⁺ in Luft mit zusÄtzlich 8% O₂ beschleunigten die Wachstumsrate. Die gleiche Menge CO₂ ^– und CO₂ ⁺ in Luft mit zusÄtzlich 8% CO₂ hemmte die Wachstumsrate, die Bildung von Chlorophyll und entkrÄftigte die Keimlinge. Es wird gezeigt,dass O₂ ^– und O₂ ⁺ die Bildung von Cytochrom und anderen eisenhaltigen Enzymen anregen durcn ihre Wirkung auf das den Fe-Stoffwechsel regulierende System der Pflanze. Die toxische Wirkung von CO₂ ^– und CO₂ ⁺ lÄsst sich noch nicht erklÄren.

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Resume On a construit un appareil permettant d'introduire dans 1'atmosphères des ions de gaz déterminés. On a alors effectué de telles adjonctions à l'air contenu dans des cellules de plastique dans lesquelles on cultivait HORDEUM VULGARIS sur du sable et dans une solution nutritive chimiquement définie. Des densités modérées d'ions O₂ ^– ou O₂ ⁺ (1,8×10⁴/cm³) dans de l'air additionné de 8% d'O₂ accélèrent la croissance. La meme concentration de CO₂ ^– et CO₂ ⁺ additionnée de 8% de CO₂ a ralenti la croissance et la formation de chlorophylle et a diminué la vitalite des plantes nouvellement germées. On démontre que O₂ ^– et O₂ ⁺ active la formation de cytochrome et d'autres enzymes ferreuses par suite de l'action de ces ions sur le système régularisant le métabolisme du fer dans la plante. L'effet toxique du CO₂ ^– et CO₂ ⁺ reste encore inexpliqué.

     

Photosynthetic/photorespiratory characteristics of C3−C4 intermediate species

The extent of photorespiration, the inhibition of apparent photosynthesis (APS) by 21% O₂, and the leaf anatomical and ultrastructural features of the naturally occurring C₃–C₄ intermediate species in the diverse Panicum, Moricandia, and Flaveria genera are between those features of representative C₃ and C₄ plants. The greatest differences between the photosynthetic/photorespiratory CO₂ exchange characteristics of the C₃–C₄ intermediates and C₃ plants occur for the parameters which are measured at low pCO₂ (i.e., the CO₂ compensation concentration and rates of CO₂ evolution into CO₂-free air in the light). The rates of APS by the intermediate species at atmospheric pCO₂ are similar to those of C₃ plants.The mechanisms which are responsible for reducing photorespiration in the C₃–C₄ intermediate species are poorly understood, but two proposals have been advanced. One emphasizes the importance of limited C₄ photosynthesis which reduces O₂ fixation by ribulose 1,5-bisphosphate carboxylase/oxygenase, and, thus, reduces photorespiration by a CO₂-concentrating mechanism, while the other emphasizes the importance of the internal recycling of photorespiratory CO₂ evolved from the chloroplast/mitochondrion-containing bundle-sheath cells. There is no evidence from recent studies that limited C₄ photosynthesis is responsible for reducing photorespiration in the intermediate Panicum and Moricandia species. However, preliminary results suggest that some, but not all, of the intermediate Flaveria species may possess a limited C₄ cycle. The importance of a chlorophyllous bundle-sheath layer in the leaves of intermediate Panicum and Moricandia species in a mechanism based on the recycling of photorespiratory CO₂ is uncertain.Therefore, although they have yet to be clearly delineated, different strategies appear to exist in the C₃–C₄ intermediate group to reduce photorespiration. Of major importance is the finding that some mechanism(s) other than Crassulacean acid metabolism or C₄ photosynthesis has (have) evolved in at least the majority of these terrestrial intermediate species to reduce the seemingly wasteful metabolic process of photorespiration.Abbreviations APS apparent (net) photosynthesis - CAM Crassulacean acid metabolism - CE carboxylation efficiency - T CO₂ compensation concentration - IRGA infrared gas analysis - P_i orthophosphate - PEP phosphoenolpyruvate - RuBP ribulose 1,5-bisphosphate Published as Paper No. 7383, Journal Series, Nebraska Agricultural Experiment Station.     

Dependence of cell membrane conductances on bathing solution HCO 3 − /CO2 inNecturus gallbladder

Summary The effects of bathing solution HCO ₃ ^– /CO₂ concentrations on baseline cell membrane voltages and resistances were measured inNecturus gallbladder epithelium with conventional intracellular microelectrode techniques. Gallbladders were bathed in either low HCO ₃ ^– /CO₂ Ringer's solutions (2.4mm HCO ₃ ^– /air or 1mm HEPES/air) or a high HCO ₃ ^– /CO₂ Ringer's (10mm HCO ₃ ^– /1% CO₂). The principal finding of these studies was that the apical membrane fractional resistance (fR _a) was higher in tissues bathed in the 10mm HCO ₃ ^– /CO₂ Ringer's, averaging 0.87±0.06, whereasfR _a averaged 0.63±0.07 and 0.48±0.08 in 2.4mm HCO ₃ ^– and 1mm HEPES, respectively. Intraepithelial cable analysis was employed to obtain estimates of the individual apical (R _a) and basolateral membrane (R _b) resistances in tissues bathed in 10mm HCO ₃ ^– /1% CO₂ Ringer's. Compared to previous resistance measurements obtained in tissues bathed in a low HCO ₃ ^– /CO₂ Ringer's, the higher value offR _a was found to be due to both an increase inR _a and a decrease inR _b. The higher values offR _a and lower values ofR _b confirm the recent observations of others. To ascertain the pathways responsible for these effects, cell membrane voltages were measured during serosal solution K⁺ and Cl^– substitutions. The results of these studies suggest that an electrodiffusive Cl^– transport mechanism exists at the basolateral membrane of tissues bathed in a 10mm HCO ₃ ^– /1% CO₂ Ringer's, which can explain in part the fall inR _b. The above observations are discussed in terms of a stimulatory effect of solution [HCO ₃ ^– /PCO₂ on transepithelial fluid transport, which results in adaptive changes in the conductive properties of the apical and basolateral membranes.     

Dynamic changes of canopy-scale mesophyll conductance to CO₂ diffusion of sunflower as affected by CO₂ concentration and abscisic acid

Leaf‐level measurements have shown that mesophyll conductance (g_m) can vary rapidly in response to CO₂ and other environmental factors, but similar studies at the canopy‐scale are missing. Here, we report the effect of short‐term variation of CO₂ concentration on canopy‐scale g_m and other CO₂ exchange parameters of sunflower (Helianthus annuus L.) stands in the presence and absence of abscisic acid (ABA) in their nutrient solution. g_m was estimated from gas exchange and on‐line carbon isotope discrimination (Δ_obs) in a ¹³CO₂/¹²CO₂ gas exchange mesocosm. The isotopic contribution of (photo)respiration to stand‐scale Δ_obs was determined with the experimental approach of Tcherkez et al. Without ABA, short‐term exposures to different CO₂ concentrations (C_a 100 to 900 µmol mol^?1) had little effect on canopy‐scale g_m. But, addition of ABA strongly altered the CO₂‐response: g_m was high (approx. 0.5 mol CO₂ m^?2 s^?1) at C_a < 200 µmol mol^?1 and decreased to <0.1 mol CO₂ m^?2 s^?1 at C_a >400 µmol mol^?1. In the absence of ABA, the contribution of (photo)respiration to stand‐scale Δ_obs was high at low C_a (7.2‰) and decreased to <2‰ at C_a > 400 µmol mol^?1. Treatment with ABA halved this effect at all C_a.     

Determination of [Mg2+]i – an update on the use of Mg2+-selective electrodes

Since their invention, ion-selective microelectrodes have become an indispensable tool for investigations of intracellular ion regulation and transport. While highly selective sensors for all major intracellular monovalent ions have been available for decades, the development of sensors for divalent cations seems to have presented more difficulties. As ion-selective microelectrodes typically have time-constants in the range of 0.5 to several seconds they turned out to be inapt for the investigation of intracellular Ca²⁺. The development of sensors for Mg²⁺-selective electrodes has made its most striking progress only over the past few years. While the first Mg²⁺ sensor, ETH 1117, was barely able to detect physiological Mg²⁺ concentrations in the presence of other mono- and divalent cations, the newest sensors allow measurements in the micromolar range. When used in macroelectrodes, the most recent developments, ETH 5506 and ETH 5504, have even been reported to do so in the presence of millimolar Ca²⁺ concentrations. Although there is still room for improvement to make these sensors applicable in microelectrodes, some preliminary data look extremely promising and indicate that a new era for Mg²⁺-selective microelectrodes is about to start.     

Characterisation of CO2 and HCO3 − uptake in the cyanobacterium Synechocystis sp. PCC6803

The availability of a complete genome database for the cyanobacterium Synechocystissp. PCC6803 (glucose-tolerant strain) has raised expectations that this organism would become a reference strain for work aimed at understanding the CO₂-concentrating mechanism (CCM) in cyanobacteria. However, the amount of physiological data available has been relatively limited. In this report we provide data on the relative contributions of net HCO₃ ⁻ uptake and CO₂ uptake under steady state photosynthetic conditions. Cells were compared after growth at high CO₂ (2% v/v in air) or limiting CO₂ conditions (20 ppm CO₂). Synechocystishas a very high dependence on net HCO₃ ⁻ uptake at low to medium concentrations of inorganic carbon (Ci). At high Ci concentrations net CO₂ uptake became more important but did not contribute more than 40% to the rate of photosynthetic O₂ evolution. The data also confirm that high Ci cells of Synechocystissp. PCC6803 possess a strong capacity for net HCO₃ ⁻ uptake under steady state photosynthetic conditions. Time course experiments show that induction of maximal Ci uptake capacity on a shift from high CO₂ to low CO₂ conditions was near completion by four hours. By contrast, relaxation of the induced state on return of cells to high CO₂, takes in excess of 230 h. Experiments were conducted to determine if Synechocystissp. PCC6803 is able to exhibit a `fast induction' response under severe Ci limitation and whether glucose was capable of causing a rapid inactivation in Ci uptake capacity. Clear evidence for either response was not found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selection of soybean plant leaves which yield mesophyll cell isolates with maximal rates of CO2 and NO inf2 sup− photoassimilation

A problem often encountered when assaying mesophyll cell isolates prepared from mature soybean leaves, was that of poor reproducibility in rates of net ¹⁴CO₂ photoassimilation and NO₂ ^– photoreduction. It was known that soybean source leaves repeatedly displayed their most active net CO₂ photoassimilation in the period from attainment of maximal leaf area to approximately two to five days subsequent to that point. Advantage was taken of the fact that when soybean leaflets of each leaf reach their maximal area they also have reached their maximal leaf length from base to tip. This facilitates a more rapid determination of the point in time in which leaflet areas had reached A_max. Soybean plants (Glycine max cv. Williams) were propagated in the growth chamber with a 12 h light-12 h dark cycle, 25C, 65% RH, and 700 microeinsteins per meter squared per second. At 24 d post-emergence, the third leaf (numbered acropetally from the unifoliates) of each plant had just attained maximum leaflet areas (110 cm²) and lengths (13 cm). For this study, leaf mesophyll cells were enzymatically isolated, using commercially prepared pectinase, from leaflet sets of leaves selected from each of the second, third, and fourth leaf positions. Maximal rates of net ¹⁴CO₂ photoassimilation (with 5 mM HCO₃ ^–) for the second, third and fourth leaf (leaflet) isolates were, respectively, 27.0, 57.0, and 41.7 mol ¹⁴CO₂ assimilated per milligram chlorophyll per hour; simultaneously maximal rates of NO _inf2 ^sup– photoreduction (1 mM NO _inf2 ^sup– ) were, respectively, 4.4, 8.1, and 0.0 mol NO _inf2 ^sup– reduced per milligram chlorophyll per hour. These studies made it clear that in order repeatedly to attain reproducible maximal rates of leaf cell isolate net ¹⁴CO₂ photoassimilation and NO _inf2 ^sup– photoreduction, it always was necessary to select the newest, fully expanded leaves (e.g. leaf number 3) for cell isolation. Leaves from several plants only were pooled if they were excised from identically the same node on each of the plants.Abbreviations A_max - maximum leaflet (trifoliolate) area attained during ontogeny - CO₂ - CO₂ gas dissolved in solution - HCO _inf3 ^sup– - bicarbonate - L_max - maximum leaf blade length (midvein) attained during ontogeny - NiRase - chloroplast nitrite reductase (reduced ferredoxin) - NiPR - nitrite photoreduction - PE - post-emergence - Pn - net CO₂ photoassimilation (for leaflets and mesophyll cell isolates) - PPRC - pentose phosphate reductive cycle     

Evidence for the involvement of (Cu-ATP)2− in the inhibition of human erythrocyte (Ca2+ + Mg2+-ATPase by copper

The effects of copper on the activity of erythrocyte $\text{(}\text{Ca}{}^{\mathrm{2+}}\text{+}\text{Mg}{}^{\mathrm{2+}}\text{)-}\text{ATPase}$ have been tested on membranes stripped of endogenous calmodulin or recombined with purified calmodulin. The interactions of copper with Ca²⁺, calmodulin and (Mg-ATP)^2? were determined by kinetic studies. The most striking result is the potent competitive inhibition exerted by (Cu-ATP)^2? against (Mg-ATP)^2?$\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 2.8 μ}\text{M}$), while free copper gives no characteristic inhibition. Our results also demonstrate that copper does not compete with calcium either on the enzyme or on calmodulin. The fixation of calmodulin on the enzyme is not altered in the presence of copper as shown by the fact that the dissociation constant remains unaffected. It may be speculated that (Cu-ATP)^2? is the active form of copper, which could plausibly be at the origin of some of the pathological features of erythrocytes observed in conditions associated with excess copper.     

A model of photosynthetic CO2 assimilation and carbon-isotope discrimination in leaves of certain C3−C4 intermediates

A model of leaf, photosynthesis has been developed for C₃–C₄ intermediate species found in the generaPanicum, Moricandia, Parthenium andMollugo where no functional C₄ pathway has been identified. Model assumptions are a functional C₃ cycle in both mesophyll and bundle-sheath cells and that glycine formed in the mesophyll, as a consequence of the oxygenase activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39), diffuses to the bundle sheath, where most of the photorespiratory CO₂ is released. The model describes the observed gas-exchange characteristics of these C₃–C₄ intermediates, such as low CO₂-compensation points () at an O₂ pressure of 200 mbar, a curvilinear response of to changing O₂ pressures, and typical responses of CO₂-assimilation rate to intercellular CO₂ pressure. The model predicts that bundle-sheath CO₂ concentration is highest at low mesophyll CO₂ pressures and decreases as mesophyll CO₂ pressure increases. A partitioning of 5–15% of the total leaf Rubisco into the bundle-sheath cells and a bundlesheath conductance similar to that proposed for C₄ species best mimics the gas-exchange results. The model predicts C₃-like carbon-isotope discrimination for photosynthesis at atmospheric levels of CO₂, but at low CO₂ pressures it predicts a higher discrimination than is typically found during C₃ photosynthesis at lower CO₂ pressures.Abbreviations and symbols PEP phosphoenolpyruvate - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) - RuBP ribulose-1,5-bisphosphate - p(CO₂) partial pressure of CO₂ - p(O₂) partial pressure of O₂. See also p. 471     

Properties of Cl−-Stimulated Mg2+-ATPase Sensitive to Ligands of Inhibitory Receptors in Brain Plasma Membranes of the Bream Abramis brama

Properties of Cl^–-stimulated Mg²⁺-ATPase in the brain plasma membranes of the bream Abramis brama L. were studied; this enzyme is composed of basal Mg²⁺-ATPase activity that can be stimulated by 40–80% by Cl^– ions (Cl^–-ATPase). These anions stimulate the basal Mg²⁺-ATPase starting with 8 mM concentration, their maximal effect being observed at a concentration of 30–100 mM. The Cl^–-ATPase activity was found at a low molarity of HEPES-Tris buffer (< 30 mM) but was not revealed at a high molarity (> 30 mM). The basal Mg²⁺-ATPase activity was detected in the whole studied pH range (5.5–9.0), with maximum at pH 7.2–7.8 values, whereas optimum to reveal Cl^–-ATPase was at high and low H⁺ concentrations (pH 6.0 and 8.5, respectively). At physiological pH values (7.2–7.5) the Cl^–-ATPase activity was not revealed, but was detected after preincubation of the enzyme with 10 µM GABA. The basal Mg²⁺-ATPase, like Cl^–-ATPase, hydrolyzed ATP with a maximal rate, while CTP, ITP, and ADP only slightly, and did not hydrolyze GTP and AMP. The Cl^–-ATPase activity decreased in the presence of divalent cations in the following order: Mg²⁺ > Co²⁺ > Mn²⁺ = Cd²⁺ > Al³⁺ = Cu²⁺, and it was not found in the presence of Ca²⁺ and Zn²⁺. Anions of halogen series activated the basal Mg²⁺-ATPase in the descending order: Cl^– > Br^– > J^– > F^–. Among other monovalent anions, HCO₃ ^– activated the enzyme, NO₃ ^– practically had no effect, and SCN^– inhibited its activity. Blockers of Cl^– transport (ethacrinic acid, furosemide, and SITS) and GABA-receptor ligands (pentobarbital, diazepam, and picrotoxin) suppressed the enzyme activity. Out of SH-reagents, PCMB inhibited the enzyme, while NEM did not affect it. The H⁺-ATPase blocker oligomycin inhibited the enzyme, while the blocker of Na⁺,K⁺-ATPase ouabain and the blocker of Ca²⁺,Mg²⁺-ATPase ruthenium red had no effect. The properties of the Cl^–-stimulated Mg²⁺-ATPase of fish brain are discussed in comparison with those of the rat brain Cl^–-ATPase. The conclusion is made that the bream brain enzyme differs markedly from Cl^–-ATPase (the ATP-dependent Cl^–-pump) of mammalian brain.