EFFECTS OF LIGHT INTENSITY AND TEMPERATURE ON CRYPTOMONAS OVATA (CRYPTOPHYCEAE) GROWTH AND NUTRIENT UPTAKE RATES1

Specific growth rate of Cryptomonas ovata var. palustris Pringsheim was measured in batch culture at 14 light-temperature combinations. Both the maximum growth rate (μ_m) and optimum light intensity (I_opt) fit an empirical function that increases exponentially with temperature up to an optimum (T_opt), then declines rapidly as temperature exceeds T_opt. Incorporation of these functions into Steele's growth equation gives a good estimate of specific growth rate over a wide range of temperature and light intensity. Rates of phosphate, ammonium and nitrate uptake were measured separately at 16 combinations of irradiance and temperature and following a spike addition of all starved cells initially took up nutrient at a rapid rate. This transitory surge was followed by a period of steady, substrate-saturated uptake that persisted until external nutrient concentration fell. Substrate-saturated NO₃^?-uptake proceeded at very slow rates in the dark and was stimulated by both increased temperature and irradiance; NH₄⁺-uptake apparently proceeded at a basal rate at 8 and l4 C and was also stimulated by increased temperature and irradiance. Rates of NH₄^?-uptake were much higher than NO₃^?-uptake at all light-temperature combinations. Below 20 C, PO₄^?3-uptake was more rapid in dark than in light, but was light enhanced at 26 C.     

Effects of temperature and dinitrophenol on the uptake of potassium and sodium ions in Ricinus communis roots

Summary Detopped root systems of Ricinus communis plants were used for the study of the effects of temperature and DNP on the uptake of K and Na ions supplied as KNO₃ and NaNO₃.When K and Na ions were offered together in equivalent concentrations, the steady state uptake rates for K⁺ and Na⁺ at 23 to 25° gave a K⁺/Na⁺ ratio of 3. Increasing the Na⁺ concentration relative to K⁺ 3-fold did not alter the preferential uptake of K⁺. The uptake of K⁺ was more sensitive to temperature in the range 10 to 40° and to the application of DNP at 1.5x10^-4 M than was the uptake of Na⁺. When NaNO₃ was the only salt supplied Na⁺ uptake became more sensitive to DNP than when both K⁺ and Na⁺ nitrates were supplied. Prolonged application of DNP led to net K⁺ efflux from the roots, even when no K⁺ was being supplied to the roots. Net Na⁺ efflux under the influence of DNP occurred only in roots previously grown on Na-containing nutrient medium.The different responses of the K⁺ and Na⁺ uptake processes to temperature and DNP suggest the operation of different uptake mechanisms for K⁺ and Na⁺ These results have been considered in relation to the recent concept of dual mechanisms for the absorption of alkali cations by plant tissues.     

Absorption of Iron by Enzymically Isolated Leaf Cells

Iron uptake was studied using cells enzymically isolated from green tobacco leaves. Absorption was increased both by light and succinate as probable energy sources. Bicarbonate in the incubation mixture was inhibitory, and citrate also reduced absorption presumably by chelation with the metal. Absorption of iron was temperature sensitive and optimal at 25°C. Temperature coefficients and activation energies suggested that absorption was energy mediated. NaN₃ and DNP inhibited uptake at concentrations of 10-³M and 10^?4M, respectively. The inhibition caused by DNP was not negated by an external supply of ATP. The results suggest that iron absorption is an active metabolic process in cells enzymically isolated from green tobacco leaves. Cells from Fe-chlorotic leaves of PI 54619–5–1 soybean absorbed less iron than those derived from healthy leaves of the same variety, while leaf cells from the variety Hawkeye showed no such differences.     

The Influence of Photosynthetic Factors and Metaholic Inhibitors on the Uptake of Phosphate in P-Deficient Scenedesmus

The cells used in the present investigation had a phosphate content of about 20 per cent as compared with the status in normal cultures. The uptake of phosphate during a period of 4 hours was determined at a pH of 6,5, kept constant with the aid of a citrate buffer. In the absence of CO₂, light increased the uptake of phosphate with saturation around 14,000 erg/cm²s. With 5 per cent CO₂ in the air the relationship was more complicated, and the uptake of phosphate must he related to more than one process during active photosynthesis. The inhibiting effect of CO₂ in air was noticeable already at low concentrations both in light and in darkness. With the system used, this supports earlier indications for internal recycling of orthophosphate, CO₂ was inhibiting also in nitrogen in the light. Selenate in a concentration of 2 mM gave a slight and rather irregular inhibition.—Anaerobiosis had no effect in the light but gave a large decrease in the dark.—DNP (0.1 mM) was somewhat more active in the dark than in the light. The lower concentrations tested had no effect in either case.—Menadione (0.1 mM) inhibited strongly, and more in illuminated than in non-illuminated cells.     

Nystatin affects zinc uptake in human fibroblasts

The mechanism(s) by which zinc is transported into cells has not been identified. Since zinc uptake is inhibited by reducing the temperature, zinc uptake may depend on the movement of plasma membrane micoenvironments, such as endocytosis or potocytosis. We investigated the potential role of potocytosis in cellular zinc uptake by incubating normal and acrodermatitis enteropathica fibroblasts with nystatin, a sterol-binding drug previously shown to inhibit potocytosis. Zinc uptake was determined during initial rates of uptake (10 min) following incubation of the fibroblasts in 50 μg nystatin/mL or 0.1% dimethyl-sulfoxide for 10 min at 37°C. The cells were then incubated with 1 to 30 μM ⁶⁵zinc. Michaelis-Menten kinetics were observed for zinc uptake. Nystatin inhibited zinc uptake in both the normal and AE fibroblasts. Reduced cellular uptake of zinc was associated with its internalization, not its external binding. In normal fibroblasts, nystatin significantly reduced theK _m 56% and theV _max 69%. In the AE fibroblasts, nystatin treatment significantly reduced theV _max 59%, but did not significantly affect theK _m. The AE mutation alone affected theV _max for cellular zinc uptake. The control AE fibroblasts exhibited a 40% reduction inV _max compared to control normal fibroblasts. We conclude that nystatin exerts its effect on zinc uptake by reducing the velocity at which zinc traverses the cell membrane, possibly through potocytosis. Furthermore, the AE mutation also effects zinc transport by reducing zinc transport.     

Zn uptake by Cladophora glomerata

The uptake of zinc by Cladophora glomerata at different pH-values, light conditions and exposure periods is reported. Zinc uptake was pH-dependent, with uptake increasing with rising pH. Uptake was greatest within the first two hours of exposure and was greater in light than in darkness due to increased pH. All results support the dominance of adsorptive uptake of zinc by Cladophora.     

The uptake and subcellular distribution of aromatic amines in the brain of the rat

The hydroxylated phenylethylamines p-tyramine, m-tyramine, octopamine, metaraminol and norepinephrine were accumulated by homogenates of rat brain much more vigorously than β-phenethylamine or amphetamine. The affinity concentrations (K_m) for initial (5-min) uptake by homogenates of whole brain were 0.5, 3 and 6 μM for DL-norepine-phrine, p-tyramine and DL-octopamine, respectively. The uptake of these three hydroxylated compounds was much more vigorous in striatal tissue than in cortical tissue, and in both tissues the rate of uptake decreased in the sequence: norepinephrine > tyramine > octopamine. The uptake of these three substances was inhibited by reduced temperature, by lack of glucose, by CN- and DNP, and by desmethylimipramine, cocaine and ouabain. The uptake of norepinephrine and octopamine appeared to require Na⁺. Pretreatment of rats with reserpine or 6-hydroxydopamine decreased the ability of brain to take up norepinephrine or octopamine. Previously accumulated labelled phenylethylamines migrated in sucrose density gradients with a peak of radioactivity corresponding to an equilibrium position of catecholamine-containing nerve endings. The magnitude of the retention of [³H]amine in this synaptosornal peak decreased in the order: norepinephrine > octopamine > tyramine. The accumulated amines were released by sonic, osmotic and thermal stresses which disrupt neuronal membranes. The presence of a β-hydroxyl group appeared to protect amines from destruction by monoamine oxidase, presumably by virtue of uptake in presynaptic storage vesicles. During superfusion, tyramine and metaraminol appeared to displace [³H]norepinephrine from binding sites in brain slices.     

Interacting effects of light,temperature, and nutrients on C-14 uptake of oscillatoria rubescens de candolle

The rate of C¹⁴O₂ uptake in a bacterized isolate of Oscillatoria rubescens indicates that within the ranges studied temperature caused the greatest variation followed by light intensity and nutrient concentration. The variation within interaction effects of light, temperature, and nutrients was higher than that within any other combination of interactions. High temperatures (25°C) shifted the light optimum of O. rubescens growing in low to moderate nutrient levels from 1950 lux to 800 lux.     

Untersuchung der Beziehung zwischen extracellulärer Glykolsäure-Ausscheidung und der photosynthetischen CO2-Aufnahme bei der Blaualge Anacystis nidulans

Summary The formations of transients in CO₂ exchange in the blue-green alga Anacystic nidulans is dependent on the temperature used during the measurements. The algae were grown in a low light intensity (4000 lux) under normal air conditions and measured in the same low CO₂ concentration (0.03 vol. %) but under a higher light intensity (10 000 lux). At a temperature of +20°C the stationary rate of CO₂ uptake was reached directly. At a temperature of +35°C, on the other hand, a maximum of CO₂ uptake could be observed at the beginning of the light period followed by a steady rate of photosynthesis, which was higher than at +20°C. In the beginning of the dark period a CO₂ outburst appeared at 35°C.Only at a low temperature (+20°C) did we find a light induced glycollate excretion; after a maximum at 7 1/2 minutes illumination the release of glycollate ceases and the level decreases to a lower value. A similar time course exists during illumination in red light (621 nm, 1.5·10^-8 einsteins) and a temperature of +20°C. In blue light (432 nm, 1,5·10^-8 einsteins, +20°C) and in white light at a high temperature (+35°C) we could not find any light induced glycollate excretion. Our results are discussed in reference to the photorespiration. We explain the formation of transients in CO₂ uptake of Anacystis at a high temperature (+35°C) and in blue light (+20°C) on the basis of the influence of photorespiration.     

TRANSPORT OF TYROSINE, PHENYLALANINE, TRYPTOPHAN AND GLYCINE IN NEUROBLASTOMA CLONES

Amino acid transport was studied in three neuroblastoma clones, N-TD6, which synthesizes norepinephrine, N-T16, which synthesizes small amounts of serotonin, and N-S20Y, which synthesizes acetylcholine. All three clones exhibited high-affinity saturable transport systems for tyrosine, phenylalanine, tryptophan and glycine as well as systems unsaturated at amino acid concentrations of 1 mM in the external medium. Tyrosine, phenylalanine and tryptophan enter all three clones by rapidly exchanging transport systems which appear to be relatively insensitive to lowered external [Na⁺] or to the presence of 2,4-dinitrophenol (DNP). Glycine uptake was slower and was much more sensitive to lowered external [Na⁺] and to the presence of DNP in the medium. Glycine transport in N-T16 cells was decreased more markedly at low temperature than was transport of the three aromatic amino acids. K_m and V_max values found for saturable transport of tyrosine, phenylalanine and tryptophan were sufficiently low to suggest that, if similar amino acid transport systems exist in neuronal membranes, and if amino acid levels in brain extracellular fluid are similar to levels in plasma, such systems may serve, in conjunction with transport systems in cerebral capillaries, to limit the entry of amino acids into brain cells when blood amino levels are near the normal physiological range.     

CO2 and water vapour exchange in four alpine herbs at two altitudes and under varying light and temperature conditions

CO₂ and water vapour exchange rates of four alpine herbs namely: Rheum emodi, R. moorcroftianum, Megacarpaea polyandra and Rumex nepalensis were studied under field conditions at 3600 m (natural habitat) and 550 m altitudes. The effect of light and temperature on CO₂ and water vapour exchange was studied in the plants grown at lower altitude. In R. moorcroftianum and R. nepalensis, the average photosynthesis rates were found to be about three times higher at 550 m as compared to that under their natural habitat. However, in M. polyandra, the CO₂ exchange rates were two times higher at 3600 m than at 550 m but in R. emodi, there were virtually no differences at the two altitudes. These results indicate the variations in the CO₂ exchange rates are species specific. The change in growth altitude does not affect this process uniformly.The transpiration rates in R. emodi and M. polyandra were found to be very high at 3600 m compared to 550 m and are attributed to overall higher stomatal conductance in plants of these species, grown at higher altitude. The mid-day closure of stomata and therefore, restriction of transpirational losses of water were observed in all the species at 550 m altitude. In addition to the effect of temperature and relative humidity, the data also indicate some endogenous rhythmic control of stomatal conductance.The temperature optima for photosynthesis was close to 30°C in M. polyandra and around 20°C in the rest of the three species. High temperature and high light intensity, as well as low temperature and high light intensity, adversely affect the net rate of photosynthesis in these species.Both light compensation point and dark respiration rate increased with increasing temperature.The effect of light was more prominent on photosynthesis than the effect of temperature, however, on transpiration the effect of temperature was more prominent than the effect of light intensity.No definite trends were found in stomatal conductance with respect to light and temperature. Generally, the stomatal conductance was highest at 20°C.The study reveals that all these species can easily be cultivated at relatively lower altitudes. However, proper agronomical methodology will need to be developed for better yields.     

RELATIONSHIP BETWEEN PHOTOSYNTHETIC OXYGEN CYCLING AND CARBON ASSIMILATION IN SYNECHOCOCCUS WH7803 (CYANOPHYTA)1

Mass spectrometric analysis of oxygen uptake and evolution in the light by marine Synechococcus WH7803 indicated that the respiration rate was near zero at low irradiance levels but increased significantly at high irradiances. The light intensity (I_r) at which oxygen uptake began to increase with increasing light intensity depended on the growth irradiance of the culture. In each case, I_r coincided with the minimum light intensity for saturation of carbon assimilation (I_k). At irradiances >I_r, net oxygen evolution rates paralleled carbon assimilation rates. Oxygen uptake at high light intensities was inhibited by DCMU, indicating that oxygen uptake was due to Mehler reaction activity. The onset of Mehler activity at I_k supports the idea that oxygen becomes an alternative sink for electrons from photosystem I when NADPH turnover is limited by the capacity of the dark reactions to utilize reductant.     

Mechanism of Zinc Uptake in Bean (Phaseolus vulgaris) Tissues

Uptake of micronutrient zinc by intact leaves, enzymically isolated leaf cells, leaf disks, excised roots, and stem-callus tissue of two field bean cultivars 'Saginaw’ and ‘Sanilac’) was studied using radio-isotope tracer technique. Radio-phosphorus absorption by these tissues was also followed under comparable experimental conditions. A rapid absorption of the micronutrient and strong dependency on external zinc concentration and pH were revealed. Absorption of zinc was not inhibited by respiratory inhibitors (dinitrophenol, azide, cyanide, and amytal), and was not light or temperature dependent. Q₁₀ values for zinc uptake ranged between 1 and 1.2. Uptake of phosphate, on the other hand, was temperature and light dependent and drastically reduced by the presence of metabolic inhibitors. Differences in responses to respiratory inhibitors, temperature, pH, light and darkness, and kinetic data, strongly suggest that zinc uptake in bean tissues occurs primarily by a passive mechanism, involving possibly a physical or physiochemical binding of the micronutrient ions to the cell wall and free space components, and a passive diffusion into the interior of the cell.     

EARLY TOXIC EFFECTS OF ZINC ON PSII OF SYNECHOCYSTIS AQUATILIS F. AQUATILIS (CYANOPHYCEAE)1

Zinc toxicity on photosynthetic activity in cells of Synechocystis aquatilis f. aquatilis Sauvageau was investigated by monitoring Hill activity and fluorescence. The oxygen‐evolving activity decreased to about 80% of the initial value after exposure to 0.1 mM ZnSO₄ for 1 h. The PSII activity was inhibited by 40% in the presence of zinc concentrations ranging from 0.5 to 5.0 mM, suggesting that the metal effect is limited by zinc uptake. The fluorescence capacity (F_max–F/F_max) decreased from 0.57 to 0.35 and 0.20 in Zn‐treated cells for 15 and 60 min, respectively, thus providing evidence for rapid inactivation of electron transport at PSII. Zinc treatment promoted a rapid increase in PSII fluorescence that was counteracted by addition of 1,4‐benzoquinone, indicating that electron transfer at the reducing side of the PSII reaction center is arrested by zinc. Furthermore, a decline in the fluorescence yield could be observed after 1 h of zinc treatment as well as when Zn‐treated cells were excited in presence of 3‐(3′,4′‐dichlorophenyl)‐1,1‐dimethylurea. Under these conditions, zinc did not affect energy transfer from phycobilisomes to PSII, and the gradual quenching of PSII fluorescence may be due to a decrease in electron flow on the donor side of PSII. However, the 20% increase in the minimal fluorescence intensity (F_o) in parallel to the absence of changes in the maximal fluorescence intensity (F_max), observed in the first hour of zinc treatment, could also suggest a metal‐induced decline in the energy transfer from PSII‐chl a antenna to the PSII reaction center.     

Sul Controllo Della Glicolisi Nel Lievito

Abstract

On the control of carbohydrate utilization in yeast. — The results of a previous investigation showed that in higher plants the stimulating action of 2,4 dinitrophenol (DNP) on oxygen uptake and glycolysis is accompained by a fall of the level of reducing sugars, due to an increase of their respiratory utilization, and thus — according to every evidence — of the rate of hexose phosphate synthesis.

In the present work, the occurrence of a similar phenomenon in yeast (where the inhibiting effect of DNP on glucose uptake is not so much marked as in higher plant tissue) was investigated.

Here again DNP, at a 10^-4M concentration, induced a rapid decrease of the disaccaride trehalose and of glycogen, such as to account for the increased rate of respiration and of fermentation. The ratio between the contributions to CO₂ of Carbons 1 and respectively 6 of glucose was not significantly changed by DNP, which suggests that at least part of the DNP induced increase of glycolysis was mediated by the Embden Meyerhof pathway, and thus that a larger amount of fructose diphosphate was formed in the presence of the uncoupler.

In other experiments the effects of DNP on the dissimilation of C¹⁴ labeled glucose, glycerol and pyruvate to CO₂ and ethanol, and on the incorporation of the radioactive isotope into various fractions, 15 minutes after feeding the labeled substrates, was investigated. It was found that:

1) Glucose and glycerol uptake is not markedly inhibited by DNP at the concentration employed (^10–4M).

2) In the absence of DNP, a considerable portion of the radioactivity fed as glucose or glycerol and taken up by the yeast cells is recovered in the glycogen and trehalose fractions. (35% of the glucose, and 22% of the glycerol taken up). This is also observed for carbons 2 and 3, but not for carbon 1 of pyruvate. This indicates a reversibility of the glycolitic processes comprehended in the region between phospho-enol pyruvate andpolysac-carides; while the pyruvate kinase reaction appears to represent a sharp barrier at the « lower » end of glycolysis.

3) DNP almost completely inhibited the incorporation of C¹⁴ from glucose and glycerol into glycogen and trehalose, although it increased the rate of its dissimilation to CO₂ and ethanol. The total amount of glucose and glycerol transformed in the various metabolites (and thus — according to every evidence — phosphorylated) was somewhat lowered and proteins synthesis severely depressed. These effects are interpreted as due to the uncoupling action of DNP at the mitochondrial level, and to the consequent general decrease of the ATP and UTP levels required for protein and for polysaccharide synthesis.     

Perturbations of malate accumulation and the endogenous rhythms of gas exchange in the Crassulacean acid metabolism plant<Emphasis Type="Italic"> Kalanchoë daigremontiana</Emphasis>: testing the tonoplast-as-oscillator model

In continuous light, leaves of the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier exhibit a circadian rhythm of CO₂ uptake, stomatal conductance and leaf-internal CO₂ pressure. According to a current quantitative model of CAM, the pacemaking mechanism involves periodic turgor-related tension and relaxation of the tonoplast, which determines the direction of the net flux of malate between the vacuole and the cytoplasm. Cytoplasmic malate, in turn, through its inhibitory effect on phosphoenolpyruvate carboxylase, controls the rate of CO₂ uptake. According to this mechanism, when the accumulation of malate is disrupted by removing CO₂ from the ambient air, the induction of a phase delay with respect to an unperturbed control plant is expected. First, using the mathematical model, such phase delays were observed in numerical simulations of three scenarios of CO₂ removal: (i) starting at a trough of CO₂ uptake, lasting for about half a cycle (ca. 12 h in vivo); (ii) with the identical starting phase, but lasting for 1.5 cycles (ca. 36 h); and (iii) starting while CO₂ increases, lasting for half a cycle again. Applying the same protocols to leaves of K. daigremontiana in vivo did not induce the predicted phase shifts, i.e. after the end of the CO₂ removal the perturbed rhythm adopted nearly the same phase as that of the control plant. Second, when leaves were exposed to a nitrogen atmosphere for three nights prior to onset of continuous light to prevent malate accumulation, a small, 4-h phase advance was observed instead of a delay, again contrary to the model-based expectations. Hence, vacuolar malic acid accumulation is ruled out as the central pacemaking process. This observation is in line with our earlier suggestion [T.P. Wyka, U. Lüttge (2003) J Exp Bot 54:1471–1479] that in extended continuous light, CO₂ uptake switches gradually from a CAM-like to a C3-like mechanism, with oscillations of the two CO₂ uptake systems being tightly coordinated. It appears that the circadian rhythm of gas exchange in this CAM plant emerges from one or several devices that are capable of generating temporal information in a robust manner, i.e. they are protected from even severe metabolic perturbations.Abbreviations CAM Crassulacean acid metabolism - c_ia Ratio of mesophyll CO₂ concentration to external CO₂ concentration - J_C Rate of carbon dioxide uptake - J_W Transpiration rate - g_W Stomatal conductance - LL Continuous light conditions - PEPC Phosphoenolpyruvate carboxylase - Rubisco d-Ribulose-1,5-bisphosphatecarboxylase/oxygenase - Effective quantum yield of photosystem II     

Ecological studies of Chloroflexis,a gliding photosynthetic bacterium

Summary Chloroflexis, a gliding, filamentous, photosynthetic bacterium, is present in the stratified algal-bacterial mats which occur in the 50°–70°C temperature range of alkaline hot spring effluents. The organism is in association with the alga in the upper, algal layer, and also forms thick, orange mats beneath the algal layer. Natural populations of Chloroflexis from these mats demonstrated light-stimulated uptake of some ¹⁴C-labelled organic compounds. Photosynthetic ¹⁴CO₂ fixation by natural samples of Chloroflexis was investigated with respect to temperature, light intensity and mat depth. Bacterial photosynthesis was determined in samples in which algae were present by use of the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Bacterial photosynthesis was maximal at depths down to about 3 mm and then decreased rapidly to very low levels at greater depths. The greatest amounts of bacteriochlorophyll pigments were also concentrated in the top 3–4 mm of the mat. The optimum light intensity for bacterial photosynthesis (about 400 ft-c) was considerably lower than the normal summer light intensity at the surface of the mat (5000-8000 ft-c).The temperature optima for photosynthesis by the bacterial component of natural mat samples from several sites of different temperatures in a hot spring thermal gradient were determined. Temperature optima approximated the environmental temperatures, indicative of the occurrence of strains of Chloroflexis adapted to different temperatures. Although bacterial standing crop was greatest in the temperature range 50°–55°C, maximum photosynthetic efficiency was observed at about 45°C. Sulfide was stimulatory to photosynthetic ¹⁴CO₂ fixation by naturally occurring populations of Chloroflexis under field conditions. These data are consistent with the hypothesis that Chloroflexis may utilize sulfide as an electron donor for photosynthetic CO₂ reduction. However, it is also likely that Chloroflexis grows photoheterotrophically in these mats, obtaining organic compounds from algal excretory products.     

Über eine Wirkung von Natrium-Ionen auf die Phosphataufnahme und die lichtabhängige Phosphorylierung von Ankistrodesmus braunii

Summary The uptake of labelled phosphate, especially the incorporation in the organic, in TCA soluble phosphate compounds of the unicellular green alga Ankistrodesmus braunii is markedly stimulated by Na⁺ more in the light but is stimulated in the dark as well (Na⁺-effect). This stimulation depends on the phosphate concentration and on the sodium concentration of the medium (optimum 10^-3M NaCl) and appears in short-time incorporations (1 min) only at low phosphate concentrations (10^-7 to 10^-5 m PO₄). In addition the Na⁺-effect depends on temperature and almost disappears at 1°C. The incorporation of ³²P in the dark is strongly inhibited by 2,4-dinitrophenol (DNP) and under this condition only a very samll increase of the ³²P incorporation by Na⁺ can be measured. In the light however the same concentration of DNP has only a low effect on ³²P incorporation in case no Na⁺ is present in the medium. If Na⁺ is present in the medium, the effect of DNP on ³²P incorporation is increased in the light. The Na⁺-effect in the light is also inhibited by di-chlorophenyl-1,1-dimethylurea (DCMU) in N₂-atmosphere. High concentrations of g-Strophantin (10^-3 m) inhibit the uptake of phosphate by Ankistrodesmus; the inhibition is more increased in the presence of KCl than in the presence of NaCl. The results clearly indicate, that Na⁺ will not effect the incorporation of labelled phosphate by means of influencing passive processes of phosphate diffusion or phosphate exchange, but acts on different energy-requiring processes of phosphorylation in dark and light. At present one could conclude, that Na⁺ acts less through a mechanism of a sodium pump, but rather affects the formation of energy-rich compounds (in the dark by way of the oxydative phosphorylation, in the light perhaps by means of the non-cyclic photosynthetic phosphorylation).     

Zinc exchange by blood cells in nearly physiologic standard conditions

Determination of zinc concentrations in white blood cells has been used to establish zinc deficiency. During pathological conditions changes in zinc concentrations in these blood cells were observed. However, these investigations were hampered by the low amount of zinc in this form per mL blood. Earlier we demonstrated that, in the case of zinc deficiency, the uptake of zinc was increased, using the in vitro exchange of zinc by the various blood cells with extracellular zinc labeled with⁶⁵Zn in fairly physiologic conditions. In case of inflammation, no increase in zinc uptake by erythrocytes was seen, indicating that this method probably can be used to differentiate real from apparent zinc deficiency. Only during the first days of the inflammatory process, probably representing the redistribution phase during which zinc moves from the serum to the liver, a small increase in in vitro zinc uptake was seen in mononuclear cells (MNC) and polymorphonuclear cells (PMNC). Earlier papers raised some questions; e.g., is the uptake part of an exchange process and can the efflux of zinc by the cells be measured by the same method; what is the influence of time on the process of zinc uptake; what is the magnitude of the uptake of zinc by the cells compared to the zinc concentration in the cells; and, what is the influence of temperature on the uptake of zinc? In the present study, the influence of incubation time and temperature on the uptake of zinc by human and rat blood cells and on the release of zinc by rat blood cells was studied. At least three phases of uptake of zinc in the various cells were found by varying the incubation time—a fast phase during the first half hour, probably caused by an aspecific binding of zinc on or in the cell membrane; a second fast uptake between 60–330 min, probably caused by an influx of zinc in the cell as part of the exchange process of zinc; and a slow third phase after 5.5 h, in which probably the in- and efflux of the rapidly exchangeable intracellular pool is more or less equilibrated. For mononuclear cells, polymorphonuclear cells, and erythrocytes of rats, the rapidly exchangeable intracellular pool is 40%, 53%, and 10%, respectively, of the total zinc content of the cells. This study is also performed in human cells; in human cells the exchangeable pool of mononuclear cells and erythrocytes is 17 and 3.5% of the total zinc content of the cells, respectively. The efflux of zinc by blood cells can be measured by the same method. Both the uptake and the loss of zinc by blood cells of rats were compared and are of the same magnitude, indicating that the in vitro uptake of zinc described elsewhere is part of an exchange process. Increasing temperature during incubation procedures results in an increase of zinc uptake by human blood cells, even at high temperatures of 41°C, although there are gradual differences between the various blood cells. Both the in- and efflux of zinc by blood cells are very small at 4°C.     

Active Silicon Uptake by Wheat

The absorption of Si by wheat, Triticum aestivum L. ‘Yecora Rojo,’ followed Michaelis–Menten kinetics over a concentration range of 0.004–1.0 mM. K_m and V_max were determined using linear transformations and the calculated curve fitted the data closely. The absorption resulted in accumulation ratios of 200/1 or more. In keeping with that finding, this study also demonstrated that Si uptake by wheat is under metabolic control, being severely restricted by dinitrophenol (DNP) and potassium cyanide (KCN). Silicon uptake by wheat was not significantly affected by phosphate ions, but the chemical analog Ge exerted a direct competitive effect on Si uptake, and vice versa.