Distribution of Intercellular Material in the Apical Part of Pea Seedlings

The sections from the upper part of the third internode, counted from the seed, in etiolated pea seedlings are studied for the distribution of two types of Intercellular spaces: the transparent and the dark. The transparent spaces represent the result of the water logging of passages originally water-lined, while the dark spaces are lined with a lipid-containing substance which may be impregnated with melted paraffin and which forms a ramifying network within the tissue. The intercellular material of the dark spaces has the appearance of a tube, since it concentrically lines the intercellular space, leaving a lumen for air or gas. It is a plastic, isotropic subslance which may be cut transversely and identified in successive sections of the inlernode as belonging to the same continuous material from the intercellular space. The dark and the transparent spaces have a distinct pattern of distribution in the growing internode, and the relative quantity of dark spaces present at different levels of the internode may be measured. The dark spaces predominate in those parts of the stem with a greater potential for growth, while the transparent spaces are located in the regions where growth has ceased or subsided. Since the paraffin is infiltrated instantaneously throughout the network of dark intercellular spaces, it is possible that these may represent a channel for the translocation of substances.     

用于研究植物质外体空间三维结构的树脂铸型技术

本文介绍了用于研究植物体质外体空间三维结构的树脂铸型技术。植物包含许多重要的质外体空间,如木质部管状分子的腔隙、与气孔相连的叶肉细胞间的通气系统、分泌腔等等。这种空间的三维结构可借助于扫描电子显微镜(SEM)研究。但问题是,用SEM直接观察不到一个组织或细胞切面内部的图像,因此,不能观察它们的全貌。通过运用树脂铸型技术,可以获得完整的组织或腔隙内部空间的铸型。反映管壁结构的各种形象被印在铸型的表面上,在SEM下可对质外体空间进行详细研究。树脂铸型技术在结构植物学的研究上有重要的意义。     

用于研究植物质外体空间三维结构的树脂铸型技术

本文介绍了用于研究植物体质外体空间三维结构的树脂铸型技术。植物包含许多重要的质外体空间,如木质部管状分子的腔隙、与气孔相连的叶肉细胞间的通气系统、分泌腔等等。这种空间的三维结构可借助于扫描电子显微镜（ＳＥＭ）研究。但问题是,用ＳＥＭ直接观察不到一个组织或细胞切面内部的图像,因此,不能观察它们的全貌。通过运用树脂铸型技术,可以获得完整的组织或腔隙内部空间的铸型。反映管壁结构的各种形象被印在铸型的表面     

Critical Point Drying Method Using Dry Ice

A critical point drying method using dry ice (solid carbon dioxide) instead of liquid carbon dioxide is reported. After the specimens are placed in the chamber of the medical point drying apparatus, dry ice cut to the shape of the chamber is inserted. The chamber is closed and warmed to change the dry ice into liquid carbon dioxide. This method needs no gas cylinder and even minute or fragile specimens do not blow away because there is no flow of gas. This method can be used with any kind of critical point drying apparatus.     

Gas Transport in the Marsh Grass, Spartina alterniflora

Spartina plants have continuous gas spaces from the leaves tothe tips of the roots. Oxygen values in the roots are as lowas 3 per cent and increase toward the stem. Carbon dioxide valuesare highest in the rhizome and decrease up the stem and towardthe root tips. Oxygen and carbon dioxide moved through the plantsat equal rates for equal gradients, and these rates agree withmeasurements made on plants in the marsh. Calculated oxygenand carbon dioxide fluxes for the observed gradients in theobserved gas spaces agreed with measured fluxes. We concludethat gases move in and out of Spartina roots by diffusion throughuninterrupted gas spaces within the plant.     

Construction and performance of plug-in membrane inlet mass spectrometer for fermentor monitoring

An in situ sterilizable plug-in membrane inlet mass spectrometer for monitoring dissolved gases and volatiles in fermentors was constructed and tested. The design ensured a minimal distance to be traveled by analyte molecules from the bulk of the fermentation broth to the ionization chamber of the mass spectrometer. Apart from the specific cross talk due to overlapping mass peaks from different compounds, we found that carbon dioxide interfered unspecifically with all the mass peaks of other substances, changing them by the same factor. The interference changed slowly with time and could be positive or negative depending on the history of the mass spectrometer. Also, the general sensitivity of the instrument changed slowly with time. These effects can be neglected or corrected for empirically in short-term measurements. When the fermentor was aerated with a three-component gas mixture including carbon dioxide, a rapid change in the partial pressure of carbon dioxide in the gas mixture gave rise to a transient in the signal of a gas whose partial pressure was kept constant. This effect revealed a transient change in the composition of the gas mixture in the bubbles caused by net import or export of carbon dioxide during equilibration with the new gas mixture. An experimental method to determine the effective partial pressures of gases in the bubbles during steady-state transport of carbon dioxide was designed. The plug-in membrane inlet mass spectrometer was tried as a probe for oxygen and ethanol in an oxystatic culture of the yeast Pichia stipitis. We found that it was possible to keep a steady-state concentration of as little as 0.5 muM throughout the lifetime of the culture. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 535-542, 1997.     

Carbon Dioxide and pH in Relation to Salt Uptake by Beetroot Tissue

The enhancement of cation uptake in beetroot disks with increasingpH is confirmed. In disks taken from growing beet, the presenceof 2 per cent carbon dioxide in air results in a further promotionof cation uptake at pH 7.4, but not at lower pH levels. Theability to respond to added carbon dioxide is often absent indisks cut from dormant roots in winter storage, but may be partlyrestored by pre-washing the disks for a suitable period. Theinfluence of various washing pre-treatrnents indicates thatthe carbon dioxide effect is most pronounced when excess cationuptake is at a maximum. The additional cation uptake at highpH with or without 2 per cent carbon dioxide, and part of thecation uptake at pH 5.6, is balanced by an equivalent synthesisof organic acids. It is concluded that cation uptake is notprimarily determined by the external bicarbonate concentration,and that the pH effect is a genuine one. An electrochemicalapproach shows that the observed effects of high pH and of carbondioxide can be largely accounted for in terms of passive diffusionof ions across the cell membrane, whilst cation accumulationat low pH may involve a hydrogen ion excretion pump.     

Mutants of Rhodospirillum rubrum Obtained After Long-Term Anaerobic, Dark Growth

Rhodospirillum rubrum S(1) cells were grown for more than 100 generations under strict anaerobic, dark conditions in liquid medium with sodium pyruvate. During this time, growth became nonpigmented. When cells were streaked onto the surface of solid growth medium in anaerobic bottles and placed in the dark, a few light-red colonies developed, but the majority was nonpigmented. Mutants were obtained from colonies selected on the basis of pigmentation and bacteriochlorophyll a content. The growth, ultrastructure, and light reactivity of two mutants were examined. Mutant C synthesized bacteriochlorophyll a (7.2 mumoles per mg of protein), altered membrane structures, and chromatophores during dark growth. Examination of light-induced changes of the absorption spectrum of this mutant suggested that only an electron transport pathway, which included the low potential cytochrome-like pigment C428, could be detected. Mutant C grew anaerobically in the light, whereas mutant G1 was light sensitive and produced only trace amounts of bacteriochlorophyll a (0.6 mumole per ml of protein). Poorly pigmented G1 cells contained unusual membrane structures. When dark-grown G1 colonies were placed in the light, deep-red colored papillae developed in the nonpigmented colonies. During anaerobic, dark growth with sodium pyruvate, both C and G1 synthesized poly-beta-hydroxybutyrate and produced acetate, carbon dioxide, and hydrogen gas.     

Determination of carbon dioxide evolution rate using on-line gas analysis during dynamic biodegradation experiments

Respirometry is a precious tool for determining the activity of microbial populations. The measurement of oxygen uptake rate is commonly used but cannot be applied in anoxic or anaerobic conditions or for insoluble substrate. Carbon dioxide production can be measured accurately by gas balance techniques, especially with an on-line infrared analyzer. Unfortunately, in dynamic systems, and hence in the case of short-term batch experiments, chemical and physical transfer limitations for carbon dioxide can be sufficient to make the observed carbon dioxide evolution rate (OCER) deduced from direct gas analysis very different from the biological carbon dioxide evolution rate (CER).To take these transfer phenomena into account and calculate the real CER, a mathematical model based on mass balance equations is proposed. In this work, the chemical equilibrium involving carbon dioxide and the measured pH evolution of the liquid medium are considered. The mass transfer from the liquid to the gas phase is described, and the response time of the analysis system is evaluated.Global mass transfer coefficients (K(L)a) for carbon dioxide and oxygen are determined and compared to one another, improving the choice of hydrodynamic hypotheses. The equations presented are found to give good predictions of the disturbance of gaseous responses during pH changes.Finally, the mathematical model developed associated with a laboratory-scale reactor, is used successfully to determine the CER in nonstationary conditions, during batch experiments performed with microorganisms coming from an activated sludge system. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 243-252, 1997.     

The fine structure of endothelium of large arteries

Endothelium of large arteries from several species was studied in thin sections with the electron microscope. Before sacrifice, some animals received an intravenous injection of colloidal thorium dioxide which was visualized in the sections. Surface replicas were prepared by carbon evaporation on either frozen-dried endothelium or on endothelium dried by sublimation of naphthalene with which the tissue had been impregnated. Cell boundaries, stained with silver, were observed in sections and also from the surface by stripping off the inner part of the endothelium. In addition to the usual cytoplasmic organelles, the endothelial cells showed certain characteristic features, namely, large invaginated pockets communicating with the arterial lumen, numerous much smaller vesicular structures immediately under the plasma membrane and apparently also communicating with the lumen, and inclusions, into which injected thorium particles were incorporated. Intercellular boundaries appeared as regular double membranes in thin sections, and they were outlined by a double row of silver granules after silver staining. No evidence was obtained of permeation of intracellular spaces by colloidal thorium.     

The Fine Structure of Endothelium of Large Arteries

Endothelium of large arteries from several species was studied in thin sections with the electron microscope. Before sacrifice, some animals received an intravenous injection of colloidal thorium dioxide which was visualized in the sections. Surface replicas were prepared by carbon evaporation on either frozen-dried endothelium or on endothelium dried by sublimation of naphthalene with which the tissue had been impregnated. Cell boundaries, stained with silver, were observed in sections and also from the surface by stripping off the inner part of the endothelium. In addition to the usual cytoplasmic organelles, the endothelial cells showed certain characteristic features, namely, large invaginated pockets communicating with the arterial lumen, numerous much smaller vesicular structures immediately under the plasma membrane and apparently also communicating with the lumen, and inclusions, into which injected thorium particles were incorporated. Intercellular boundaries appeared as regular double membranes in thin sections, and they were outlined by a double row of silver granules after silver staining. No evidence was obtained of permeation of intracellular spaces by colloidal thorium.     

Understanding in vivo carbon precursor supply for fatty acid synthesis in leaf tissue

The principal supply of carbon precursors for fatty acid synthesis in leaf tissue has been a much debated topic, with some experiments suggesting a direct supply from the C3 products of photosynthetic carbon fixation and colleagues suggesting the utilization of free acetate (for which concentrations in leaves in the range of 0.05-1.4 mM have been reported). To address this issue we first reassessed the in vivo rate of fatty acid synthesis using a new method, that of [13C]carbon dioxide labeling of intact Arabidopsis plants with the subsequent analysis of fatty acids by gas chromatography-mass spectrometry (GC-MS). This method gave an average value of 2.3 mmoles carbon atoms h-1 mg chlorophyll-1 for photosynthetic tissues. The method was extended by isotopic dilution analysis to measure the rate of fatty acid synthesis in the dark. There was negligible fatty acid synthesis (< 5% of the rate in the light) in the dark. In addition, the method allowed an estimate of the absolute rate of fatty acid degradation of about 4% of the total fatty acid content per day. With the in vivo rate of fatty acid synthesis in the light defined, if the bulk tissue acetate concentration available for fatty acid synthesis is 1 mM, this acetate pool can sustain fatty acid synthesis for approximately 60 min. When the leaves of Arabidopsis, barley and pea were given a 5 min pulse of [14C]carbon dioxide, the label rapidly appeared in fatty acids with a lag phase of less than 2-3 min. Continuous labeling with [14C]carbon dioxide, for up to 1 h, showed a similar result. Furthermore, 14C-label in free acetate was less than 5% of that in fatty acids. In conclusion, these data suggest that either the bulk pool of acetate is not involved in fatty acid synthesis or the concentration of acetate must be less than 0.05 mM under strong illumination.     

Thiosulfate stimulation of microbial dark assimilation of carbon dioxide in shallow marine waters

The effect of thiosulfate on dark assimilation of carbon dioxide in shallow marine environments was investigated in order to explain the recent discovery of bacterial thiosulfate oxidation in aerobic, open ocean seawater. The results demonstrate that the potential exists for microbial thiosulfate oxidation to increase both dark assimilation of carbon dioxide and the utilization of organic compounds in the sea. Thiosulfate-stimulated microbial activity may be caused not only by chemoautotrophic sulfur bacteria, but also by heterotrophic species which oxidize thiosulfate to tetrathionate. Measurements of dark assimilation of carbon dioxide made at different incubation times indicate that great care must be taken both in experimental procedure and in interpretation of results obtained with the dark assimilation technique.     

A respirometer for organ cultures

1. A differential respirometer that can measure the oxygen uptake of organ cultures for periods of several days is described. 2. Diethanolamine is used as an external carbon dioxide buffer so that oxygen consumption can be measured in the presence of physiological concentrations of carbon dioxide and bicarbonate. 3. The efficiency of carbon dioxide retention with 5% carbon dioxide as gas phase is estimated to be 75% and the accuracy to be +/-5% with a measured rate of oxygen uptake in excess of 40mul./hr. 4. Some experiments with guinea-pig retina are reported.     

A field enclosure apparatus for measuring crop photosynthesis

The field enclosure is a transparent box covering a soil area of 1.5 m². It is a semi-closed system in which concentrations of water vapour and carbon dioxide are maintained constant: the required rate of input of carbon dioxide being a measure of the photosynthesis rate, and the rate of condensation of water, on cooling coils, a measure of transpiration. The air within the enclosure is circulated rapidly by fans to decrease concentration gradients, and under steady radiation inputs the air temperature is controlled to ±0.5 °C. Both photosynthesis and transpiration rates are corrected for air exchange with the surroundings, as measured through the injection of the inert gas, nitrous oxide.     

Stomatal conductance, photosynthesis and respiration of temperate deciduous tree seedlings grown outdoors at an elevated concentration of carbon dioxide

Seedlings of temperate deciduous tree species were grown outdoors at ambient and at an elevated concentration of carbon dioxide to examine how aspects of their gas exchange would be altered by growth at elevated carbon dioxide concentration. Leaf conductances to water vapour and net carbon dioxide exchange rates were determined periodically near midday. Whole-plant carbon dioxide efflux rates in darkness were also determined. The stomatal conductance of leaves of plants grown and measured at 700 cm³ m^?3 carbon dioxide did not differ from that of plants grown and measured at 350 cm³ m^?3 in Malus domestica, Quercus prinus and Quercus robur at any measurement time. In Acer saccharinum, lower conductances occurred for plants grown and measured at elevated carbon dioxide concentration only at measurement temperatures above 33°C. Photo-synthetic adjustment to elevated carbon dioxide concentration was evident only in Q. robur. All species examined had lower rates of dark respiration per unit of mass when grown and measured at elevated carbon dioxide concentration.     

Physiological studies on nitrogen fixation in the blue-green alga anabaena cylindrica

Summary Short-term manometric experiments with bacteria-free cultures of Anabaena cylindrica showed that the close dependency of nitrogen fixation upon photosynthesis could be temporarily eliminated in nitrogen-starved cells. Initial rates of nitrogen uptake by these cells in the absence of carbon dioxide were equally rapid in the light and dark, decreasing and finally ceasing after two hours. Continued steady nitrogen uptake was only maintained for long periods in the presence of carbon dioxide in the light. In the dark, nitrogen uptake was accompanied by carbon dioxide evolution.More oxygen was evolved in the light by cells fixing nitrogen than by those incubated under argon. This additional oxygen evolution could be accounted for by extra carbon dioxide fixation in the presence of nitrogen.Of a number of organic compounds tested, only sodium pyruvate stimulated nitrogen fixation. This stimulation was achieved both in the light and dark and in the presence and absence of carbon dioxide, showing that the role of pyruvate was other than acting as a carbon skeleton.Three metabolic inhibitors, cyanide and chlorpromazine (chiefly respiratory) and phenylurethane (photosynthetic) differentially inhibited photosynthesis and nitrogen fixation. The latter inhibitor had a more marked effect on photosynthesis while the two chiefly respiratory inhibitors had a stronger effect on nitrogen fixation.     

Underwater photosynthesis in flooded terrestrial plants: a matter of leaf plasticity

BACKGROUND: Flooding causes substantial stress for terrestrial plants, particularly if the floodwater completely submerges the shoot. The main problems during submergence are shortage of oxygen due to the slow diffusion rates of gases in water, and depletion of carbohydrates, which is the substrate for respiration. These two factors together lead to loss of biomass and eventually death of the submerged plants. Although conditions under water are unfavourable with respect to light and carbon dioxide supply, photosynthesis may provide both oxygen and carbohydrates, resulting in continuation of aerobic respiration. SCOPE: This review focuses on evidence in the literature that photosynthesis contributes to survival of terrestrial plants during complete submergence. Furthermore, we discuss relevant morphological and physiological responses of the shoot of terrestrial plant species that enable the positive effects of light on underwater plant performance. CONCLUSIONS: Light increases the survival of terrestrial plants under water, indicating that photosynthesis commonly occurs under these submerged conditions. Such underwater photosynthesis increases both internal oxygen concentrations and carbohydrate contents, compared with plants submerged in the dark, and thereby alleviates the adverse effects of flooding. Additionally, several terrestrial species show high plasticity with respect to their leaf development. In a number of species, leaf morphology changes in response to submergence, probably to facilitate underwater gas exchange. Such increased gas exchange may result in higher assimilation rates, and lower carbon dioxide compensation points under water, which is particularly important at the low carbon dioxide concentrations observed in the field. As a result of higher internal carbon dioxide concentrations in submergence-acclimated plants, underwater photorespiration rates are expected to be lower than in non-acclimated plants. Furthermore, the regulatory mechanisms that induce the switch from terrestrial to submergence-acclimated leaves may be controlled by the same pathways as described for heterophyllous aquatic plants.     

THE CHLOROPHYLL-CARBON DIOXIDE RATIO DURING PHOTOSYNTHESIS

Using a rapid spectrographic method of carbon dioxide measurement previously described by McAlister (1937) further studies on the time course of photosynthesis in the higher plant, wheat, variety Marquis, are herein reported. Of major importance in this work is the discovery of a pick-up of carbon dioxide in darkness immediately following a high rate of photosynthesis (see Figs. 3 and 4). This pick-up is believed to be due to the action of a carbon dioxide-combining intermediate; i.e., the "acceptor molecule" for carbon dioxide in photosynthesis. The conditions under which this phenomenon has so far been observed indicate that the intermediate is formed in relatively large quantities during the actual process of photosynthesis and not before. That the intermediate is chlorophyllous in nature is suggested by a simple stoichiometry of the order of unity that is found to exist between the number of carbon dioxide molecules taken up and the total number of chlorophyll molecules present in the plant. This is in opposition to the idea of a large photosynthetic unit of some 2000 chlorophyll molecules operating together in the reduction of 1 carbon dioxide molecule. Further studies of the induction phase under various conditions of previous dark rest and of carbon dioxide and light limitation are herein described. Employing the simple hypothesis that the number of carbon dioxide molecules not reduced during the induction period (induction loss) gives a measure of the number of elementary photosynthetic cycles unoperative or compensated for during induction together with the experimental fact that this induction loss is of the order of the total number of chlorophyll molecules present, these latter studies also indicate, in a less direct manner, that chlorophyll participates in photosynthesis as an individual molecule and not as part of a very large multimolecular chlorophyll unit. The fast dark reaction lasting about 1 minute (Fig. 7) required to reproduce both (a) the phenomena of induction in carbon dioxide assimilation and (b) the recovery of fluorescence of chlorophyll in leaves in darkness as observed by Franck and Wood (1936), demonstrates a close relationship between the fluorescence of chlorophyll and induction in photosynthesis. The rate of respiration (carbon dioxide production) of the higher plant, wheat, was measured under intense illumination and in the absence of carbon dioxide (to suppress assimilation). This value was found to be identical with the dark respirational rate measured before and after the light period, indicating very positively the absence of any direct effect of light on respiration.     

Ternary effects on the gas exchange of isotopologues of carbon dioxide

The ternary effects of transpiration rate on the rate of assimilation of carbon dioxide through stomata, and on the calculation of the intercellular concentration of carbon dioxide, are now included in standard gas exchange studies. However, the equations for carbon isotope discrimination and for the exchange of oxygen isotopologues of carbon dioxide ignore ternary effects. Here we introduce equations to take them into account. The ternary effect is greatest when the leaf-to-air vapour mole fraction difference is greatest, and its impact is greatest on parameters derived by difference, such as the mesophyll resistance to CO(2) assimilation, r(m) . We show that the mesophyll resistance to CO(2) assimilation has been underestimated in the past. The impact is also large when there is a large difference in isotopic composition between the CO(2) inside the leaf and that in the air. We show that this partially reconciles estimates of the oxygen isotopic composition of CO(2) in the chloroplast and mitochondria in the light and in the dark, with values close to equilibrium with the estimated oxygen isotopic composition of water at the sites of evaporation within the leaf.