Cellular changes during boron-deficient culture of the diatom Cylindrotheca fusiformis

The effects of boron-deficient culture were studied on the unicellular diatom. Cylindrotheca fusiformis Reimann and Lewin. After 24 to 30 h, cell division was almost completely inhibited in boron-deficient cultures. By 48 h of culture, boron-deficient diatoms had approximately twice the modal cell volume of control cells, and at least twice the amount of organic constituents such as protein (2.0x), insoluble carbohydrate (2.4x), total phenols (2.6x), and chlorophyll at (2.1x). Boron deficiency led to irreversible damage after this time.
Dark respiration was 1 nmol O₂/min × 10⁶ cells for both control and boron-deficient diatoms prior to 40 h of culture. By 48 h, the respiratory rate of boron-deficient diatoms was double that of controls. The proportion of ¹⁴C-glucose metabolized by the pentose phosphate pathway was similar in both control and boron-deficient diatoms after 24 and 48 h of culture. After 24 h, the in vitro activity of glucose-6-phosphate dehydrogenase was similar in both control and boron-deficient cells, although the pool size of its substrate, glucose-6-phosphate, was 26% greater in boron-deficient cells. The cellular amount of glucose-6-phosphate dehydrogenase continued to increase once mitosis was arrested in boron-deficient diatoms. Boric acid (1 mM) inhibited 6-phosphogluconate dehydrogenase by 18% in diatom homogenates.
During the early stages of boron deficiency, the uptake of silicate, nitrate, and phosphate, and the in vitro activity of β-glucosidase were similar to control diatoms. After cell division was inhibited, boron-deficient diatoms accumulated more nitrate and phosphate, and retained a higher level of β-glucosidase than control cells.     

Essentiality of Boron for Dinitrogen Fixation in Anabaena sp. PCC 7119

The relationship between the requirement for boron and the form of N supplied in nutrient media to cyanobacterium Anabaena sp. PCC 7119 was investigated. When cells were grown in a medium which contained nitrate or ammonium-N, boron deficiency in the nutrient media did not inhibit growth or change cell composition. However, when cells were dependent on N₂ fixation, the lack of boron inhibited growth (i.e. growth ceased after 96 hours under these conditions). Additionally, boron-deficient cells showed a significant decrease in their content of phycobiliproteins and chlorophyll and accumulated carbohydrates within 24 hours of removing boron from the nutrient media. Inhibition of photosynthetic O₂ evolution accompanied the decrease in photosynthetic pigments. Boron deficiency symptoms were relieved when either boron or combined N was added to boron-deficient cultures. The degree of recovery depended upon the age of the cultures. Assays of nitrogenase activity showed that, after 2 hours of growth, nitrogenase activity of boron-deficient cells was inhibited by 40%. After 24 hours a total inactivation of nitrogenase activity was observed in boron-deficient cells. These results strongly suggest an involvement of boron in N₂ fixation in cyanobacteria.     

Volume- and catecholamine-dependent regulation of Na/H antiporter and unidirectional potassium fluxes in Salmo trutta red blood cells

β-Adrenergic- and volume-dependent regulation of ²²Na influx and ⁸⁶Rb influx and efflux in erythrocytes of brown trout (Salmo trutta m. lacustris) were studied. Norepinephrine (10^-6 mol·1^-1) increased the rate of ²²Na influx 10-to 20-fold via the activation of a Na/H exchanger (ethyl isopropyl amiloride inhibited component of ²²Na influx). Unlike carp erythrocytes the activity of the Na, K-pump (ouabain-inhibited ⁸⁶Rb influx) was only slightly (25–35%) increased by norepinephrine. The norepinephrine-induced increment of Na, K-pump activity was completely abolished by ethyl isopropyl amiloride thus indicating that this effect was mediated by Na/H exchanger-induced increase of intracellular Na⁺ concentration. Cell shrinkage in hyperosmotic media resulted in a several-fold activation of the Na/H exchanger. Cell swelling in hypotonic media increased both the rate of K, Cl-cotransport [((dihydroindenyl)oxy)alcanaic acidsensitive components of ⁸⁶Rb influxe and efflux] and passive permeability (leakage) of erythrocyte membranes for Na⁺ and K⁺. No volume-dependent regulation of Na, K, 2Cl-cotransport (bumetanide-sensitive components of ⁸⁶Rb fluxes) was found. It may be concluded that the regulation of monovalent cation transport in erythrocytes of fast-moving (carnivorous) brown trout differs essentially from that in slowly moving (herbivorous) carp.     

Aspects toxiques du cuivre sur la biomasse et la productivité du phytoplancton de la rivière du Saguenay,Québec

In 1979 and 1980, batch culture experiments were conducted to observe the inhibitory effect of copper ion (concentrations of 10, 50, 100, 200 and 400 µg Cu · l^–1) on the standing crops and photosynthesis of phytoplankton of the Saguenay River (for 124 hours) and in Chlorella vulgaris (for 8 days). These algal assays were carried out using the surface water of the Saguenay River. In natural populatoins of phytoplankton, it was found that photosynthesis was more sensitive than growth: at the lowest concentrations, such as 10 µg Cu · 1^–1, copper seemed to increase the chlorophyll concentrations whereas the rates of primary production show a decrease of 60% with respect to the control. At higher concentrations of copper, the effect is weak in chlorophyll concentrations and more pronounced in the rates of primary production (decrease of 86 to 90%). The pennate diatoms are dominant (in all the samples) and these organisms are known as relatively resistant to copper. In Chlorella vulgaris, it was observed that with 100 µg Cu · 1^–1, chlorophyll concentrations and rates of photosynthesis respectively decrease by 63 and 99% with respect to the control. At higher concentrations of copper, a maximum decrease of 70% and 99% respectively for chlorophyll concentrations and rates of primaryproduction are observed.

     

Regulation of 86Rb influx during accumulation of Rb+ or K+ in yeast

The influx rate of ⁸⁶Rb decreases during accumulation of K⁺ or Rb⁺ into metabolizing yeast cells under anaerobic conditions with glucose as substrate. Possible causes for the decrease in the influx rate are examined. It is ruled out that the decrease in the influx rate is caused by an increased turgor pressure of the cells or to an impairment of their energization. During the accumulation of K⁺ or Rb⁺, no decrease but an increase in the protonmotive force of the cells is found. The concomitant increase in cell pH accounts only in small part for the decrease in the influx rates. Acidification of the cells on adding butyrate to the suspension causes a transient increase in the influx rates, whereas the cellular monovalent cation content is still increased. Consequently, no direct relationship is found between the influx rate and the cellular content of K⁺ and Rb⁺.     

Characterisation of a Na+/K+/Cl- cotransporter in alkylating agent-sensitive L1210 murine leukemia cells

The mode of influx of 86Rb+, a K+ congener, to exponentially proliferating L1210 murine leukemia cells, incubated in a Krebs-Ringer buffer, has been characterised. The influx was composed of a ouabain-sensitive fraction (approx. 40%), a loop diuretic-sensitive fraction (approx. 40%) and a fraction which was insensitive to both types of inhibitor (approx. 15%). The fraction of ouabain-insensitive 86Rb+ influx, which was fully inhibited by furosemide (1 mM) or bumetanide (100 microM), was completely inhibited when Cl- was completely substituted by nitrate or gluconate ions, but was slightly (29 +/- 12%) stimulated if the Cl- was substituted by Br-. The substitution of Na+ by Li+, choline or tetramethylammonium ions inhibited the loop diuretic-sensitive fraction of 86Rb+ uptake. These results suggested that a component of 86Rb+ influx to L1210 cells was mediated via a Na+/K+/Cl- cotransporter. 86Rb+ efflux from L1210 cells which had been equilibrated with 86Rb+ and incubated in the presence or absence of 1 mM ouabain, was insensitive to the loop diuretics. Additionally, efflux rates were found to be independent of the external concentration of K+, suggesting that efflux was not mediated by K+-K+ exchange. The initial rate of 86Rb+ influx to L1210 cells in the plateau phase of growth was reduced to 44% of that of exponentially dividing cells, the reduction being accounted for by significant decreases in both ouabain- and loop diuretic-sensitive influx; these cells were reduced in volume compared to cells in the exponential phase of cell growth. In cells which had been deprived of serum for 18 h, and which showed an increase of the proportion of cells in the G1 phase of the cell cycle, the addition of serum stimulated an immediate increase in the furosemide-sensitive component of 86Rb+ influx. Diuretic-sensitive 86Rb+ influx was not altered by the incubation of the cells with 100 microM dibutyryl cyclic AMP, but was inhibited by 10 microM of the cross-linking agent nitrogen mustard (bis(2-chloro-ethyl)methylamine, HN2).     

Responsiveness of a human parotid epithelial cell line (HSY) to autonomic stimulation: Muscarinic control of K+ transport

Summary Salivary electrolyte secretion is under the control of the autonomic nervous system. In this paper we report that HSY, an epithelial cell line derived from the acinar-intercalated duct region of the human parotid gland, responds to muscarinic-cholinergic (generation of Ca²⁺ signal) andβ-adrenergic (generation of cAMP signal), but not toα-adrenergic (lack of Ca²⁺ signal), receptor stimulation. The muscarinic response was studied in detail. Carbachol (10⁻⁴ M, muscarinic agonist) or A23187 (5 μM, calcium ionophore) stimulation of HSY cells increases both⁸⁶Rb (K⁺) influx and efflux, resulting in no change in net equilibrium⁸⁶Rb content. Atropine (10⁻⁵ M, muscarinic antagonist) blocks both the carbachol-generated Ca²⁺ signal and carbachol-stimulated⁸⁶Rb fluxes, but has no effect on either the A23187-generated Ca²⁺ signal or A23187-stimulated⁸⁶Rb fluxes. Carbachol- and A23187-stimulated⁸⁶Rb fluxes are substantially inhibited by two K⁺ channel blockers, quinine (0.3 mM) and scorpion venom containing charybdotoxin (33 μg/ml). The inhibition of these stimulated fluxes by another K⁺ channel blocker, tetraethylammonium chloride (5 mM), is less pronounced. Protein kinase C (PKC) seems to be involved in the regulation of the⁸⁶Rb fluxes as 10⁻⁷ M PMA (phorbol ester, phorbol-12-myristate-13-acetate) substantially inhibits the muscarinic-stimulated⁸⁶Rb efflux and influx. Because this concentration of PMA totally inhibits the carbachol-generated Ca²⁺ signal and only 80% of the muscarinic-stimulated⁸⁶Rb influx, it seems that a portion of the carbachol-stimulated⁸⁶Rb flux (i.e. that portion not inhibited by PMA) might occur independently of the Ca²⁺ signal. PMA fails to inhibit the A23187-stimulated⁸⁶Rb fluxes, however, suggesting that PKC regulates Ca²⁺-sensitive K⁺ channel activity by regulating the Ca²⁺ signal, and not steps distal to this event. 4-α-Phorbol-12,13-didecanoate, a phorbol ester which fails to activate PKC, fails to inhibit either the carbachol-stimulated increase in intracellular free Ca²⁺, or carbachol-stimulated⁸⁶Rb fluxes.     

Bumetanide-sensitive Ion Fluxes in Vascular Smooth Muscle Cells: Lack of Functional Na+, K+, 2 Cl− Cotransport

To examine the involvement of Na⁺,K⁺,2Cl⁻ cotransport in monovalent ion fluxes in vascular smooth muscle cells (VSMC), we compared the effect of bumetanide on ⁸⁶Rb, ³⁶Cl and ²²Na uptake by quiescent cultures of VSMC from rat aorta. Under basal conditions, the values of bumetanide-sensitive (BS) inward and outward ⁸⁶Rb fluxes were not different. Bumetanide decreased basal ⁸⁶Rb uptake by 70–75% with a K _i of ∼0.2–0.3 μm. At concentrations ranging up to 1 μm, bumetanide did not affect ³⁶Cl influx and reduced it by 20–30% in the range from 3 to 100 μm. In contrast to ⁸⁶Rb and ³⁶Cl influx, bumetanide did not inhibit ²²Na uptake by VSMC. BS ⁸⁶Rb uptake was completely abolished in Na⁺- or Cl⁻-free media. In contrast to ⁸⁶Rb, basal BS ³⁶Cl influx was not affected by Na⁺ _o and K⁺ _o . Hyperosmotic and isosmotic shrinkage of VSMC increased ⁸⁶Rb and ³⁶Cl influx to the same extent. Shrinkage-induced increments of ⁸⁶Rb and ³⁶Cl uptake were completely abolished by bumetanide with a K _i or ∼0.3 μm. Shrinkage did not induce BS ⁸⁶Rb and ³⁶Cl influx in (Na⁺ or Cl⁻)- and (Na⁺ or K⁺)-depleted media, respectively. In the presence of an inhibitor of Na⁺/H⁺ exchange (EIPA), neither hyperosmotic nor isosmotic shrinkage activated ²²Na influx. Bumetanide (1 μm) did not modify basal VSMC volume and intracellular content of sodium, potassium and chloride but abolished the regulatory volume increase in isosmotically-shrunken VSMC. These data demonstrate the absence of the functional Na⁺,K⁺,2Cl⁻ cotransporter in VSMC and suggest that in these cells basal and shrinkage-induced BS K⁺ influx is mediated by (Na⁺ _o + Cl⁻ _o )-dependent K⁺/K⁺ exchange and Na⁺ _o -dependent K⁺,Cl⁻ cotransport, respectively. Received: 30 January 1996/Revised: 20 May 1996     

Boron Deficiency and Translocation Profiles in Sunflower

The distribution of carbon-14 down the stems of comparable boron-deficient and boron-sufficient sunflower plants after photosynthesis of ¹⁴CO₂ by a single exposed leaf was investigated. In boron-deficient plants the advancing front of radioactivity was always found less far down the stem than in boron-sufficient plants. The general shape of the profile is the same in the two sets of plants. We conclude that the velocity of translocation is reduced in the boron-deficient plants.     

Size scaling of extracellular carbonic anhydrase activity in centric marine diatoms

Many microalgae have a surface‐associated extracellular carbonic anhydrase (eCA) that converts HCO₃^? to CO₂ for uptake and subsequent photosynthetic fixation. We investigated eCA activity and assessed its importance for photosynthetic CO₂ supply in six centric diatom species spanning nearly the full range of cell sizes for centric diatoms (equivalent spherical radius 3–67 μm). Since larger cells are more susceptible to diffusion limitation, we hypothesized that eCA activity would increase with cell size as would its importance for CO₂ supply. eCA activity did increase with cell size, increasing with cell radius by a size‐scaling exponent of 2.6 ± 0.3. The rapid increase in eCA activity with cell radius keeps the absolute CO₂ concentration difference between bulk seawater and the cell surface very low (<~0.2 μM) allowing high rates of CO₂ uptake even for large diatoms. Although inhibiting eCA did reduce photosynthesis in the diatoms, there was no overall relationship between the extent of inhibition of photosynthesis and cell size. The only indication that eCA may be more important for larger diatoms was that photosynthesis in the smallest diatoms (<4 μm radius) was only affected by eCA inhibition when CO₂ concentrations were very low, while photosynthesis in some larger diatoms was affected even at typical seawater CO₂ concentrations. eCA is ubiquitous in centric marine diatoms, in contrast to other taxa where its presence is irregularly distributed among different species, and plays an important role in supplying CO₂ for photosynthesis across the size spectrum.     

INFLUENCE OF FERULIC ACID ON MINERAL DEPLETION AND UPTAKE OF 86Rb BY PAUL'S SCARLET ROSE CELL-SUSPENSION CULTURES

The influence of 10^-4 m ferulic acid on mineral depletion and ion uptake in sterile cultures of Paul's Scarlet rose was examined. The effect of ferulic acid on the rate of depletion of Mg²⁺, Ca²⁺, K⁺, P, Fe³⁺, Mn²⁺, and Mo³⁺ from the medium during the 14-day growth cycle varied with the age of the cells and the ion under consideration. In general, rates of uptake were higher than control rates in older cells and less than control rates in cells 3–5 days old. The degree of inhibition of uptake of ⁸⁶Rb also varied with age. Young (4–5 day) cells showed approximately 50% inhibition at high concentrations of RbCl (system 2) and approximately 25% inhibition at low concentrations of RbCl (system 1). In contrast, the rate of ⁸⁶Rb uptake in 10-day cells was not significantly altered by incubation in ferulic acid.     

Photoinhibition and P700 in the Marine Diatom Amphora sp

The marine diatom Amphora sp. was grown at a light intensity of 7.0 × 10¹⁵ quanta centimeter⁻² second⁻¹. Light saturation of photosynthesis for these cells was between 6.0 and 7.0 × 10¹⁶ quanta centimeter⁻² second⁻¹. At light intensities greater than saturation, photosynthetic ¹⁴CO₂ fixation was depressed, while P700 unit size (chlorophyll a concentration/P700 activity) increased and number of P700 units per cell decreased. After a 1-hour exposure of Amphora sp. to a photoinhibitory light intensity of 2.45 × 10¹⁷ quanta centimeter⁻² second⁻¹, there was a 45 to 50% decrease in the rate of ¹⁴CO₂ fixation relative to the rate at the culture light intensity. There also was a 25% increase in P700 unit size and a 30% reduction in the number of P700 units per cell but no change in total chlorophyll a concentration. Following this period of photoinhibition, the cells were returned to a light regime similar to that in the original culture conditions. Within 1 hour, both number of P700 units per cell and P700 unit size returned to levels similar to those of cells which were kept at the culture light intensity. The rates of photosynthesis did not recover as rapidly, requiring 2 to 3 hours to return to the rate for the nonphotoinhibited cells. Our results indicate that a decrease in P700 activity (with a resultant increase in P700 unit size) may be partially responsible for the photoinhibition of algal photosynthetic carbon dioxide fixation.     

Differential calcium dependence of contractile responses and 86Rb efflux from the rabbit aorta induced by vasoactive stimuli

⁸⁶Rb was used to monitor potassium movements in strips of rabbit aorta simultaneously with measurements of tension. Histamine, noradrenaline, the prostaglandin endoperoxide analogue U46619, angiotensin II, and 144 mM K⁺ each induced an increase in ⁸⁶Rb efflux concomitantly with contraction. For the first four agonists there was a rank-order correlation between the contractile response and ⁸⁶Rb efflux, but 144 mM K⁺ induced a massive increase in ⁸⁶Rb efflux although it was the weakest contractile stimulus. Contraction and increase in ⁸⁶Rb efflux-induced K⁺ were both reduced by verapamil, which blocks voltage-sensitive calcium channels, implying that both effects of K⁺ were mediated mainly by a depolarisation-induced influx of calcium. Noradrenaline increased both tension and ⁸⁶Rb efflux through an action on alpha-adrenoceptors, but its effect on efflux, unlike its effect on tension, was apparently totally dependent on the presence of extracellular calcium. Experiments performed in the presence of lanthanum, which blocks calcium influx, showed that the intracellular store of calcium released by noradrenaline apparently played no role in inducing ⁸⁶Rb efflux, although it could trigger contraction. Lanthanum also blocked contraction induced by K⁺ but less effect on the increase in ⁸⁶Rb efflux induced by K⁺. Thus, agonist-induced vascular contraction and ⁸⁶Rb efflux can be dissociated, but under normal conditions all the contractile stimuli tested induced ⁸⁶Rb efflux.     

Orthophosphate influx and efflux rates of Chlorella fusca measured in a continuous turbidostat culture with 32P under various conditions

The main objective of the experiments with Chlorella fusca strain 211-8b was to measure, with adequate time resolution, the unidirectional influx rates of phosphate into non-phosphate-starved algae under different steady state conditions (light, temperature, 3-phosphoglycerate influence) or following the addition of several photosynthesis and phosphate transport inhibitors (phenylmercuric acetate, p-chloromercuribenzoate, arsenate). the algae were cultivated in a phosphate rich medium in a continuous turbidostat culture. The phosphate exchange experiments with carrier-free ³²PO ₄ ^3- were performed directly in the continuous culture. The sampling intervals after the tracer addition were 15 s.For a continuous steady state culture grown in the light (25° C) the unidirectional influx rate measured with ³²P is 260 times higher than the net uptake rate (=influx minus efflux rate) calculated from the mass balance using the data of this culture. In all experiments, except the control experiment with trichloroacetic acid killed cells, the specific activity of the intracellular inorganic orthophosphate compartment oscillates around a constant mean value which never reaches the specific activity of the nutrient medium within the duration of the short-term experiments (7.5 min). The inhibitors strongly affect the characteristics of the oscillations. The unidirectional influx rates are constant. Oscillating flushing rates with unlabelled phosphate from a storage compartment have been postulates to explain the oscillations. Oscillating rates from the individual cells are apparently synchronized by an unknown mechanism.     

Effect of cadmium and nickel on photosynthesis and the enzymes of the photosynthetic carbon reduction cycle in pigeonpea (Cajanus cajan L.)

The effect of Cd²⁺ and Ni²⁺ on the rate of photosynthesis and activities of key enzymes of the photosynthetic carbon reduction cycle was examined in leaves from pigeonpea (Cajanus cajan L., cv. UPAS-120) grown in nitrogen free sand culture. Two different concentrations of Cd²⁺ and Ni²⁺ were applied through the rooting medium at two growth stages. The application of Cd²⁺ and Ni²⁺ (0.5 and 1.0 mM) at an early vegetative stage (30 days after sowing) resulted in about 50% and 32% reduction in net photosynthesis, respectively. However, enzyme activities were decreased to different levels (2–61%) depending upon the enzyme and the concentration of the metal ion.These concentrations (0.5 and 1.0 mM of Cd²⁺ and Ni²⁺) had no effect when applied at a later vegetative stage i.e. 70 days after sowing. However, when the concentration of Cd²⁺ was increased to 10 mM, there was about an 86% reduction in the rate of photosynthesis but the enzyme activities were reduced by only about 40%. Although Ni²⁺ reduced the photosynthetic rate by 65%, it had little effect on enzyme activities. The reduction in photosynthesis seems to occur indirectly through a decrease in chlorophyll content and stomatal conductance but not due to decreased enzyme activities. Oxygen evolution by leaf discs was inhibited by Cd²⁺ and Ni²⁺ in parallel with a reduction in photosynthesis. These data confirm the earlier reported effects of Cd²⁺ and Ni²⁺ on O₂ evolution in isolated chloroplasts.Abbreviations FBPase Fructose-1,6-bisphosphatase - PCR Photosynthetic carbon reduction - 3-PGA 3-Phospho-glycric acid - RUBP Ribulose, 1,5-bisphosphate     

Basic characterization of an ouabain-resistant,bumetanide-sensitive K+ carrier-mediated transport system in J774.2 mouse macrophage-like cell line and in variants deficient in adenylate cyclase and cAMP-dependent protein kinase activities

⁸⁶Rb(K⁺) transport across the plasma membrane of macrophage-like cells was studied. The cells used were the wild-type J774.2 and its two variants, CT2 cells, deficient in adenylate cyclase, and J7H1 cells, deficient in cAMP-dependent protein kinase. In the three cell lines about 15% of the total ⁸⁶Rb(K⁺) influx is transported by the K⁺ carrier-mediated transport system. The ⁸⁶Rb(K⁺) efflux carried by the same transporter is negligible when measured in the absence of ouabain in the medium. Therefore this carrier conducts a net inward flux of K⁺ under the experimental conditions used. The transporter is sensitive to extracellular Na⁺ and inhibited by ‘loop’ diuretics; bumetanide inhibits ouabain-resistant ⁸⁶Rb(K⁺) influx with IC₅₀ of 0.1, 5.0, and 0.05 μM for J774.2, CT2 and J7H1 macrophages, respectively. The membrane potential of the three cells was measured, using the distribution of [³H]tetraphenylphosphonium ([³H]TPP⁺) across the plasma membrane, and found to be −80.1, −108.5 and −105.1 mV for J774.2, CT2 and J7H1 cells, respectively. The addition of bumetanide to the cell medium does not alter [³H]TPP⁺ uptake indicating that the transporter is electrically silent. It is concluded that despite the differences in cAMP metabolism by the three macrophages, the basic characteristics of K⁺ carrier-mediated transport system of the three cells are very similar.     

Early transport changes during erythroid differentiation of Friend leukemic cells

Early transport changes occurring during Friend erythroleukemic cell differentiation are reported. A decrease in the rate of 86Rb transport was observed beginning approximately five hours after stimulation with 1.5% dimethylsulfoxide (DMSO), a potent inducer of Friend cell differentiation. By 12 to 14 hours after DMSO addition, the transport rate had stabilized at close to 60% of control level. This decrease in the rate of 86Rb transport preceded a previously reported decrease in cell volume. Other chemical inducers of Friend cells, such as hypoxanthine and ouabain, also caused early decreases in 86Rb influx. In contrast, xanthine, which does not induce Friend cell differentiation, also did not affect 86Rb influx. The transport of two amino acid analogues, alpha-aminoisobutyric acid and 2-aminobicyclo [2,2,1]-heptane-2-carboxylic acid, which differ in their mode of uptake, was also measured following induction by DMSO. The transport rates of both compounds decreased after a 12-hour exposure to DMSO. In contrast, the uptake of 3H-colchicine, a drug which diffuses passively across the cell membrane, was not significantly affected. Studies with several variant cell lines which do not synthesize hemoglobin in response to DMSO indicate that these non-inducible cells can be divided into two classes--those that demonstrate early changes in transport very similar to the changes observed in inducible cell lines and those which exhibit only small changes in transport. Results obtained using a revertant clone have helped to distinguish between those transport changes which are associated with the induction of hemoglobin synthesis and those which are not. In addition, these early transport changes may be useful in defining the stage in the differentiation process at which a particular variant line is blocked.     

Action Spectrum of Photosynthesis for Skeletonema costatum Obtained with Carbon-14

The quantized action spectrum of photosynthesis for Skeletonema costatum was obtained from values of photosynthetic ¹⁴CO₂ uptake at various wavelengths of light isolated “with a diffraction grating monochromator. The quantized action spectrum of photosynthesis exhibited maxima at wavelengths similar to maxima in the absorption spectrum, in vivo, of a suspension of S. costatum cells. While the ¹⁴CO₂ technique will provide an accurate action spectrum of photosynthesis for diatoms, a large number of samples is required in order to minimize sampling error.     

Marine Plankton Algae Grown with Light-Dark Cycles.

The diatoms Ditylum brightwellii and Nitzschia turgidula were grown in semi-continuous culture under various combinations of light intensity, temperature and daylength (photoperiod). Growth was strongly limited by light intensities below 0.03 cal/em². min in both species. Above this intensity, light saturation of growth was rapidly approached in Nitzschia but only gradually so in Ditylum. The growth rate in continuous light was never significantly higher than with 16 hours of light plus 8 hours of dark. In Ditylum, continuous light above 0.03 cal/cm². min caused a strong inhibition of growth at all temperatures. The chlorophyll concentration in the cells was greater the shorter the photopceriod. In cultures synchronised by different combinations of light intensity and photoperiod, cell division generally took place in the light. Synchrony was best under short photoperiods of bright light. Time courses are shown for chlorophyll synthesis and photosynthesis in synchronised cultures.     

Regulatory interaction of ATP Na+ and Cl- in the turnover cycle of the NaK2Cl cotransporter

To probe the mechanism by which intracellular ATP, Na+, and Cl- influence the activity of the NaK2Cl cotransporter, we measured bumetanide-sensitive (BS) 86Rb fluxes in the osteosarcoma cell line UMR- 106-01. Under physiological gradients of Na+, K+, and Cl-, depleting cellular ATP by incubation with deoxyglucose and antimycin A (DOG/AA) for 20 min at 37 degrees C reduced BS 86Rb uptake from 6 to 1 nmol/mg protein per min. Similar incubation with 0.5 mM ouabain to inhibit the Na+ pump had no effect on the uptake, excluding the possibility that DOG/AA inhibited the uptake by modifying the cellular Na+ and K+ gradients. Loading the cells with Na+ and depleting them of K+ by a 2-3- h incubation with ouabain or DOG/AA increased the rate of BS 86Rb uptake to approximately 12 nmol/mg protein per min. The unidirectional BS 86Rb influx into control cells was approximately 10 times faster than the unidirectional BS 86Rb efflux. On the other hand, at steady state the unidirectional BS 86Rb influx and efflux in ouabain-treated cells were similar, suggesting that most of the BS 86Rb uptake into the ouabain-treated cells is due to K+/K+ exchange. The entire BS 86Rb uptake into ouabain-treated cells was insensitive to depletion of cellular ATP. However, the influx could be converted to ATP-sensitive influx by reducing cellular Cl- and/or Na+ in ouabain-treated cells to impose conditions for net uptake of the ions. The BS 86Rb uptake in ouabain-treated cells required the presence of Na+, K+, and Cl- in the extracellular medium. Thus, loading the cells with Na+ induced rapid 86Rb (K+) influx and efflux which, unlike net uptake, were insensitive to cellular ATP. Therefore, we suggest that ATP regulates a step in the turnover cycle of the cotransporter that is required for net but not K+/K+ exchange fluxes. Depleting control cells of Cl- increased BS 86Rb uptake from medium-containing physiological Na+ and K+ concentrations from 6 to approximately 15 nmol/mg protein per min. The uptake was blocked by depletion of cellular ATP with DOG/AA and required the presence of all three ions in the external medium. Thus, intracellular Cl- appears to influence net uptake by the cotransporter. Depletion of intracellular Na+ was as effective as depletion of Cl- in stimulating BS 86Rb uptake.(ABSTRACT TRUNCATED AT 400 WORDS)