Stoichiometry of proton uptake in isolated pea chloroplasts under different light intensities

The number of protons released inside the chloroplast thylakoids per electron which is transferred through the electron transport chain (H⁺/e^– ratio) was measured in isolated pea chloroplasts at pH 6.0 under continuous illumination and with methyl viologen as an electron acceptor. At saturating light intensity (200 W · m^–2) (strong light) the H⁺/e^– ratio was 3. At low intensity (0.9 W · m^–2) (weak light) the H⁺/e^– ratio was 2 with dark-adapted chloroplasts, but it was close to 3 with chloroplasts that were preilluminated with strong light. It is shown that the presence of azide in the reaction mixture leads to errors in the determination of the H⁺/e^– ratio due to underestimation of the initial rate of H⁺ efflux on switching off the light. To explain the above data, we assume that transformation of the electron transport chain occurs during illumination with strong light, namely, the Q cycle becomes operative.     

Regulation of photosynthetic carbon assimilation at the cellular level: a review

In green leaves and a number of algae, photosynthetically derived carbon is ultimately converted into two carbohydrate end-products, sucrose and starch. Drainage of carbon from the Calvin cycle proceeds via triose phosphate, fructose 6-phosphate and glycollate. Gluconeogenesis in photosynthetic cells is controlled by light, inorganic phosphate and phosphorylated sugars. Light stimulates the production of dihydroxyacetone phosphate, the initial substrate for sucrose and starch synthesis, and inhibits the degradative pathways in the chloroplast. Phosphate inactivates reactions of synthesis and activates reactions of degradation. Among the phosphorylated sugars a special role is allocated to fructose 2,6-bisphosphate, which is present in the cytoplasm at very low concentrations and inhibits sucrose synthesis directly by inactivating pyrophosphatedependent phosphofructokinase. The synthesis of sucrose plays a central role in the partitioning of photosynthetic carbon. The cytoplasmic enzymes, fructose bisphosphate phosphatase and sucrose phosphate synthase are likely key points of regulation. The regulation is carried out by several effector metabolites. Fructose 2,6-bisphosphate is likely to be the main coordinator of the rate of sucrose synthesis, hence of photosynthetic carbon partitioning between sucrose and starch.Paper presented at the FESP meeting (Strasbourg, 1984)     

Photosynthesis,water use and growth of a C4 grass stand at high CO2 concentration

Leaf photosynthesis rate of the C₄ species Paspalum plicatulum Michx was virtually CO₂-saturated at normal atmospheric CO₂ concentration but transpiration decreased as CO₂ was increased above normal concentrations thereby increasing transpiration efficiency. To test whether this leaf response led growth to be CO₂-sensitive when water supply was restricted, plants were grown in sealed pots of soil as miniature swards. Water was supplied either daily to maintain a constant water table, or at three growth restricting levels on a 5-day drying cycle. Plants were either in a cabinet with normal air (340 mol (CO₂) mol^-1 (air)) or with 250 mol mol^-1 enrichment. Harvesting was by several cycles of defoliation.With abundant water supply high CO₂ concentration did not cause increased growth, but it did not cause an increase in growth over a wide range of growth-limiting water supplies either. Only when water supply was less than 30–50% of the amount used by the stand with a water-table was there evidence that dry weight growth was enhanced by high CO₂. In addition, with successive regrowth, the enhancing effect under a regime of minimal water allocations, became attenuated. Examination of leaf gas exchange, growth and water use data showed that in the long term stomatal conductance responses were of little significance in matching plant water use to low water allocation; regulation of leaf area was the mechanism through which consumption matched supply. Since high CO₂ effects operate principally via stomatal conductance in C₄ species, we postulate that for this species higher CO₂ concentrations expected globally in future will not have much effect on long term growth.     

The Escherichia coli cell cycle

This review summarizes present knowledge of the bacterial cell cycle with particular emphasis on Escherichia coli. We discuss data coming from three different types of approaches to the study of cell extension and division: The search for discrete events occurring once per division cycle. It is generally agreed that the initiation and termination of DNA replication and cell septation are discrete events; there is less agreement on the sudden doubling in rate of cell surface extension, murein biosynthesis and the synthesis of membrane proteins and phospholipids. We discuss what is known about the temporal relationship amongst the various cyclic events studied. The search for discrete growth zones in the cell envelope layers. We discuss conflicting reports on the existence of murein growth zones and protein insertion sites in the inner and outer membranes. Elucidation of the mechanism regulating the initiation of DNA replication. The concept of "critical initiation mass" is examined. We review data suggesting that the DNA is attached to the envelope and discuss the role of the latter in the initiation of DNA replication.     

Morphohistochemical changes in hepatocytes during the life cycle of the European eel

The comparative analysis of morphological, histochemical and cytochemical patterns of eel (Anguilla anguilla L.) hepatocytes reveals clear differences between two stages of its life cycle, i.e. the trophic stage (yellow eel) and reproductive stage (silver eel). The storage of glycogen prevails in the yellow eel, whilst lipids appear to be remarkably increased in the silver eel, in which some hepatocytes also show glycogen-rich areas. Generally, in the silver eel dehydrogenase and acid phosphatase activities seem greater and different distribution of the reaction products is present; on the contrary, a lower G6PDH activity is observed. The electron microscopy characteristics and distribution of both cellular organelles and reserve materials reflect the modifications found at light microscopy. The ultrastructural patterns provide further evidence for the heterogeneity of liver parenchyma in silver eel. In particular, the coexistence of nuclei showing a different degree of chromatin compactness is also accounted for by the quantitative cytochemical data on the nuclear DNA after Feulgen reaction and intercalation with propidium iodide at low and high concentrations. With regard to the DNA content, the hepatocytes in the silver eel as well as in the yellow eel are mainly 2c. However, some 4c values are also found, which according to the literature can be ascribed to cells in G2 phase. The present data may express the onset of different functional requirements during the reproductive stage in comparison with the trophic one. Moreover, our results are consistent with modifications found by other authors as a consequence of interruption of nourishment and during gonad maturation, i.e. two phenomena characterizing the transition from yellow to silver eel.     

Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach

Abstract The quantitative approach used here is based on a model comprising a well-stirred medium, an unstirred layer, and a CO₂ absorbing leaf. The unstirred layer is divided up by planes into a number of sub-layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value. An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub-layers, the fluxes across the sub-layers and the conversions among the carbon components can be estimated. The CO₂ flux decreases, and the HCO^?₃ flux increases towards the leaf. There are negative fluxes of OH^& and CO^2–₃. H⁺ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non-inorganic C buffers with appropriate pK_a are present. The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast. It is argued that even better effects are possible if the back-diffusion of CO^2–₃ could be prevented by lowering the pH of the unstirred layer.     

CO2 uptake and transport in leaf mesophyll cells

Abstract The acquisition of inorganic carbon for photosynthetic assimilation by leaf mesophyll cells and chloroplasts is discussed with particular reference to membrane permeation of CO₂ and HCO^?₃. Experimental evidence indicates that at the apoplast pH normally experienced by leaf mesophyll cells (pH 6–7) CO₂ is the principal species of inorganic carbon taken up. Uptake of HCO^?₃ may also occur under certain circumstances (i.e. pH 8.5), but its contribution to the net flux of inorganic carbon is small and HCO^?₃ uptake does not function as a CO₂-concentrating mechanism. Similarly, CO₂ rather than HCO^?₃ appears to be the species of inorganic carbon which permeates the chloroplast envelope. In contrast to many C₃ aquatic plants and C₄ plants, C₃ terrestrial plants lack specialized mechanisms for the acquisition and transport of inorganic carbon from the intercellular environment to the site of photosynthetic carboxylation, but rely upon the diffusive uptake of CO₂.     

Inhibition of the formation of lipid-linked intermediates in normal and transformed cells by a purified tunicamycin homologue

Summary The deffects of a purified homologue of tunicamycin (B₂-tunicamycin) on the biosynthesis of lipid-linked intermediates participating in protein glycosylation in normal embryonic fibroblasts, 3T3 and virally transformed (simian virus 40 and polyoma virus) mouse fibroblasts grown in culture were investigated. Long incubations (20 h) with the antibiotic caused a higher degree of inhibition of sugar incorporation into glycoproteins in transformed cells. However, the formation of lipid-linked intermediates was inhibited to a similar level in both cell types. When time dependent inhibition experiments were carried out using transformed cells, an earlier and stronger inhibition of the formation of lipid-oligosaccharides occurred (70% inhibition at 30 min). In 3T3 cells, prolonged incubation (6–8 h) was necessary in order to reach a similar degree of inhibition. Formation of lipid-sugar was also inhibited to a greater extent by B₂-tunicamycin in transformed cells. This inhibition was not clearly time dependent. Analysis of the newly synthesized glycolipids in 3T3 and in transformed cells after B₂-tunicamycin treatment have shown reduction in dolichyl-P-P-sugars as well as in other glycolipids. Dimethylsulfoxide (10%) and linoleic acid (0.5 mg/ml) markedly increased the level of tunicamycin activity in 3T3 cells while phosphatidylcholine (2 mg/ml) partially reversed it. The stronger and faster inhibition of the formation of lipid intermediates of the dolichyl-phosphate cycle caused by B₂-tunicamycin in transformed cells, described here for the first time, may therefore be due to differences in penetration of the antibiotic into these cells.Abbreviations DMEM Dulbecco's modified Eagle's medium - DMSO dimethylsulfoxide - MF mouse fibroblasts from Balb/c mouse embryos - 3T3 Balb/3T3 mouse fibroblastic line - SV40 Simian virus 40 - PY polyoma virus - TLC thin layer chromatography     

Termination of parental care due to small clutch size in the temperate damselfish,Chromis notata

Synopsis Reproductive behavior of the temperate damselfish, Chromis notata, was investigated on the island of Mukaishima, Japan, almost daily during the breeding season in 1982. Both males and females repeated reproductive cycles many times during the breeding season. Females had a strong tendency to spawn a whole clutch on one nest during a few hours. The average number of eggs which a male gained per reproductive cycle was estimated at 38560 (480–131100 eggs). Males ordinarily cared for eggs until just prior to hatching, but abandoned more than half of the nests with the eggs numbering less than 11568. Contribution 207 from the Mukaishima Marine Biological Station.     

A Hypernychthemeral Sleep-Wake Syndrome: A Treatment Attempt

The wake and sleep-onset times of a patient with a sleep-wake cycle longer than 24 hr were recorded by the patient for 4 years. During this time, the patient found himself unable to maintain a 24-hr sleep-wake schedule. When treated with 1-2 mg clonazepam, taken nightly, he was able to become entrained to a 24-hr day. Despite entrainment of his sleep-wake cycle, the patient reported depression, lack of motivation and fatigue and chose not to continue taking the drug.