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Ion Distribution and Transport in the Red Marine Alga, Gracilaria Foliifera

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... S. latissima and C. crispus revealed a greater Na loss during rehydration when compared with the boiling period. The Na location in the macroalgae could justify this pattern of variation since, in some species, this element is mainly found in the superficial area of the seaweeds, as suggested by other studies (Gutknecht, 1965;Raven, 1976). L. digitata and S. latissima revealed the highest leachable fraction of this element, 60.7%, and 51.2%, respectively, during the 20 min boiling period. ...
Article
Considering the importance of seaweeds for the development of sustainable and innovative food products, this study aimed to characterize the impact of hydrothermal processing on iodine, sodium, potassium, selenium, and arsenic concentrations of four seaweed species (S. latissima, L. digitata, U. pinnatifida, and C. crispus) and on the associated health risks-benefits for consumers. These elements revealed a common pattern for leachable fractions of iodine, total arsenic, and selenium: L. digitata ≥ S. latissima > C. crispus > U. pinnatifida after rehydration and boiling during different periods. The behavior for sodium was: S. latissima > L. digitata > C. crispus > U. pinnatifida, and for potassium: U. pinnatifida > L. digitata > S. latissima > C. crispus. Generally, the species that attained more significant losses were S. latissima and L. digitata. A health-relevant sodium/potassium ratio below 0.7 was found for all species except for U. pinnatifida. In some species, the risk-benefit analysis revealed that high iodine and arsenic levels might promote risks for consumption, even after 20 min boiling, but 5 g of processed U. pinnatifida could contribute to adequate iodine, sodium, potassium, and selenium intakes for all population groups. Standardized processing treatments of seaweeds can open new opportunities for the sector.
... Agar yield decreased significantly in all ionic profiles compared to the 255 natural population (62.4 %db). In addition, agar yield of G. cliftonii in 25 Pedersen, 1991;Gutknecht, 1965;285 Lapointe, Rice, Lawrence, 1984;Ugarte, Santelices, 1992), the effect of different ionic 286 profiles of ISW on growth of seaweeds has not been reported. 287 ...
Article
Increase in salinity of inland water sources is adversely affecting aquatic and terrestrial ecosystems around the world including Australia. Inland saline water (ISW) with similar ionic profile to ocean water has potential for culturing marine species. Gracilaria species are commercially important as they are a source of agar. One of the native species Gracilaria cliftonii has been reported for high agar yield of 52%dw. The aim of this research was to investigate the feasibility of culturing G. cliftonii in different ionic profiles of ISW under laboratory conditions. The growth rate of G. cliftonii under different ionic profiles ranged from 0.9 to 2.5%day-1. Gracilaria cliftonii carbohydrate content decreased while protein content increased in culture conditions as when compared to natural populations. Agar yield, gel strength and melting point decreased while gelling temperature and sulphate content increased in culture conditions as when compared to natural populations. Strong correlation (R2 >0.8, P <0.05) was observed between K+, Na+, Ca2+, and Mg2+ content in tissue and water indicating ionic regulation by G. cliftonii. This research provides basic information and presents supportive arguments for G. cliftonii as a potential species for inland saline water aquaculture.
... The required hydrogen peroxide originates through leakage of internal produced hydrogen peroxide via the Mehler reaction (Mehler 1951) and from extracellular production by an enzymatic reduction of oxygen at the cell surface (Palenik et al. 1987). The HOI being an uncharged molecule can freely pass through the cell wall and once inside the cell it is believed to be reduced back to iodide by reactions with cellular components like glutathione (GSH) and bound intracellular (Shaw 1959, Gutknecht 1965. ...
Thesis
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The role of halogene species like iodine in the ocean and how their speciation is affected by marine organisms is not well known. This lack of knowledge demands for more detailed field as well as experimental studies in order to unravel the role of iodine in marine ecosystems. My thesis comprises field work on the iodine speciation in polar and tropical marine environments complemented by a set of laboratory experiments on the role of phytoplankton species from the two regions studied for the iodine biogeochemical cycle. A large scale survey across the Atlantic sector of the Southern Ocean and three cruises to the Mauritanian upwelling region during both strong and weak upwelling seasons provide valuable information on iodine speciation over large spatial scales in case of the former survey, and on seasonal variability in case of the latter cruises. Furthermore, comparison of these two oceanic provinces will allow to decipher differences and conformities in iodine speciation between areas as far apart as the Southern Ocean and the Mauritanian upwelling region. In both provinces the total iodine (iodate + iodide) concentrations were in the same range between 450-480nmol L-1, while surface iodide values in the euphotic zone varied considerably and showed a steep vertical concentration gradient of less than 20nmol L-1 for antarctic and over 200nmol L-1 for tropical waters. In seawater the interconversion of the two inorganic forms of iodine, iodate and iodide, can be mediated by abiotic and/or biotic processes. The accumulation of iodide in the euphotic zone in both regions is suggested to be a more biologically mediated process and as observed in the experimental studies phytoplankton cells do influence the iodate reduction to iodide. However, highest iodide concentrations were not coupled to highest biological productivity instead we observed highest iodide values during post bloom periods in the respective regions indicating a strong relationship between iodide production and phytoplankton senescence during bloom collapse. Interestingly, productive regions with high phytoplankton biomass measured as chlorophyll-a show a decline in surface iodide and also the experimental study revealed an iodide decline in cultures with viable cells suggesting that an iodide oxidation or uptake mechanism is present when cells are in the exponential growth phase. Upwelled water was lower in surface iodide compared to water from a weak-upwelling scenario, and could on one hand be traced by its lower iodide concentrations while in the Weddell Sea Basin we observed elevated iodide in the deep Weddell Sea Bottom Water (WSBW) which could be traced on the other hand by its elevated iodide concentrations. From these results it appears that iodide can be used as a tracer for upwelled water on continental shelves and for newly formed WSBW. From the results gained in the laboratory we can say that iodide formation and senescence in phytoplankton cells are coupled. Iodide production was found to be species specific and not related to chlorophyll-a, cell size or cell numbers. Moreover iodide concentrations peaked in the stationary and/or senescence growth phase. A shift from senescence back to the exponential growth phase resulted in a decline in iodide concentrations indicating that phytoplankton mediated oxidation of iodide to iodate was triggering this shift. In summary, the results of my thesis show that the combined effects of abiotic and biotic processes resulting in iodate reduction are coupled via phytoplankton senescence. These findings challenge the conventional view, as described in other studies, that iodate reduction in the ocean is directly coupled to nutrient uptake and biological production.
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The resting membrane potential of Nitella cells shifts in parallel with the change in H+ equilibrium potential, but is not equal to the H+ equilibrium potential. The deviation of the membrane potential from the H+ equilibrium potential depends on the extrusion rate of H+ by the electrogenic H+-pump. The activity of the electrogenic H+-pump was formulated in terms of the change in the free energy of ATP hydrolysis. The deviation of membrane potential from the H+ equilibrium potential induces a passive H+ flow. The passive inward H+ current may be coupled with Cl- uptake. The coupling rate of H+,Cl- co-transport was discussed. The membrane potential of mitochondria was electrochemically formulated in terms of oxidation-reduction H2/H+ half-cells spontaneously formed at the inner and outer boundaries of each trans-membrane electron-conducting pathway. The membrane potential formed by a pair of H2/H+ redox cells is pH-sensitive in its nature, but deviates from the H+ equilibrium potential to an extent that depends on the logarithm of the ratio of H2 concentrations at the inner and outer boundaries. The membrane potential of thylakoids is considered to be primarily due to the electromotive force of photocells embedded in the thylakoid membrane, as far as the anode and cathode of each photocell are in contact with the inner and outer solutions, respectively. The light-induced electronic current yields oxygen at the inner boundary and causes an increase in the H2 pool at the outer boundary of the electron-conducting pathway, which has no shunting plastoquinone chain between these two boundaries.
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Interrelationships between potassium-ion transport and transplasmalemma electrical-potential difference (AΨm.) have been investigated in Anabaena variabilis (ATCC 29413) by measuring K⁺ translocation and membrane potential in parallel. At pH 7.0, 5 mmol · dm⁻³ external K⁺, there was a thirtyfold accumulation of K⁺. The K⁺ equilibrium potential was lower (more negative) than the measured membrane potential by up to 20 mV, (ΔΨK+=–90 mV; ΔΨm=–70 mV to –75 mV, respectively). Dark pretreatment and low temperature (4°C) reduced internal K⁺ and depolarized ΔΨm. External pH affected K⁺ translocation and membrane potential; ΔΨm was hyperpolarized at high external pH; transplasmalemma K⁺ fluxes and internal K⁺ concentration were also increased at high pH. The effects of pH upon ΔΨm. coupled with the finding that the membrane potential was relatively insensitive to external K⁺, suggest that ΔΨm is unlikely to be due primarily to a diffusion potential of K⁺, but that the membrane potential is maintained by an electrogenic proton-extrusion mechanism.
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Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (I(sc)) was 97 pEq/cm(2) sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm(2) sec) and large net influxes of K (80 pEq/cm(2) sec) and Cl (50 pEq/cm(2) sec). Unidirectional K influx was proportional to I(sc), but more than one-half of the I(sc) remained unaccounted for. Both the I(sc) and PD were partly light-dependent, declining rapidly during the first 1-2 min of darkness. Ouabain (5 x 10(-4)M) had little effect on the influx of Na or K and had no effect on I(inf) or PD. Fluid was absorbed at a rate of about 93 pliter/cm(2) sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared.
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The concentrations of K, Na, and Cl in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and Cl and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and Cl and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low temperature indicate that most of the tracer K and Cl influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efflux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.
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1.1. Potassium efflux from Chlorella cells was studied by means of radiotracer.2.2. The kinetics of the efflux suggested that the exchange of the majority of the internal K+ is controlled by a first-order process.3.3. The efflux rate under conditions of no net K+ movement is approx. 1 pmole K+ per sec per cm2 in the light but falls to 0.3 pmole K+ per per cm2 for dark treated cells.4.4. The efflux was sensitive to temperature and metabolic inhibitors in a way not expected for a simple passive leak through a relatively permeable membrane.5.5. In the absence of external K+ the efflux was very low and not until this cation or Rb+ was replaced in the suspension medium did the cells readily lose tracer.6.6. The eesults are t entatively interpreted in terms of a metabolically controlled K+-K+ exchange system possibly involving a membrane carrier.
Article
1.1. Using radiotracer it has been shown that under steady-state conditions the majority of the intracellular K+ in Chlorella exchanges by first-order kinetics.2.2. The unidirectional influx of K+, in the absence of net movement, is approximately 1 pmole K+ per sec·cm2 in the light but in the dark is reduced to 0.18 pmole K+ per sec·cm2.3.3. The influx rates, particularly for illuminated cells, were temperature sensitive and seem to be under metabolic control as expected for an active process.4.4. The experiments suggest that the ligh-induced transport mechanism is independent of net carbon fixation and may be utilizing energy derived directly from electron transport processes.5.5. An estimate of the passive permeability coefficient for K+ movement into illuminated Chlorella cells gave a value of 2.0·10−8 cm·sec−1.
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The determination of Cl- in plant tissues was investigated by FeSCN2+ spectrophotometry following SCN- displacement from Hg(SCN)2 by Cl-. The calibration curve was nonlinear, but consistent and reproducible. As little as 10 nmol Cl- could be measured. There was no obvious interference in color development by water-soluble components in plant tissues. Values obtained by this method were in close agreement with those obtained potentiometrically and by coulometric titration.
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The transport of sodium through the marine algae Ulva lobata and Ulva expansa has been studied by a tracer analytical method. Sodium was transported across Ulva at a rate of 0.15% per min in the dark; this rate was slowed by ouabain and increased by formaldehyde. Dinitrophenol, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and ammonium ion had no effect on the dark rate. Light caused a transient, rapid light extrusion of sodium from the algae equal to approximately twice the amount of sodium expected during a two minute dark period. All the inhibitors adversely affected the efflux of sodium due to light. Comparison of the ability of choline and sucrose to elute sodium from Ulva showed that a high portion of the sodium can be released, but only by a process similar to ion exchange.
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Radioisotope equilibration techniques have been used to determine the intracellular concentration of K⁺, Na⁺ and Cl−, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of ⁴²K⁺, ²⁴Na⁺ and ³⁶C1⁻ are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K⁺ and Cl⁻ and against Na⁺. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K⁺ and Cl⁻ influx and Na⁺ efflux. ‘Active’ uptake and ‘passive’ loss of K⁺ and Cl⁻ are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K⁺ and Cl⁻ may be due to ‘exchange diffusion’ (K⁺/K⁺ and Cl⁻/Cl⁻antiport).
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Marine phytoplanktonic cells can achieve neutral buoyancy only if the excess density of their relatively heavy structural materials (proteins, carbohydrates, silicate) is compensated for by the incorporation of materials that have densities less than seawater. We have calculated densities and osmotic concentrations for several marine algae, based on published values of structural materials and concentrations of inorganic ions and other osmolytes. The calculations, incorporating the partial molal volume, molecular mass, concentrations and osmotic coefficients, indicate that most published listings of intracellular osmolytes in marine algae are insufficient to provide the turgor known to exist. Similarly, the density of phytoplanktonic cells, calculated on the basis of known or estimated concentrations of cellular components, generally exceeds the density of seawater, which would cause negative buoyancy (sinking) throughout. We use models of osmotic concentration and cellular density in which we supplement known concentrations of osmolytes with proxy osmolytes. In particular, concentrations of some 100 mol m-3 of quaternary ammonium derivatives can explain the deficits of both osmotic concentration and buoyancy.
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The membrane potentials of the plasmalemma and tonoplast in Griffithsia pacifica Kyl were measured and shown to be significantly different. No consistent cell wall potential was discovered. Adjacent cells in the filament were demonstrated to be electrolonically coupled with a mean coupling coefficient of 0.13. Cobaltions did not move between cells. No dye coupling was seen using the fluorescent dye Lucifer yellow CH. These observations provide new information on the electrophysiology of red algae and indicate that there is intercellular continuity between the cells of a filament of Griffithsia pacifica.
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The content of the heterosides floridoside and digeneaside and of the main ions Na+, K+, and Cl− was estimated in 20 species of the Rhodophyceae. Methods for quantitative determination of the heterosides are described. The floridoside content is in the range of 1.5–8% on a dry weight basis (Catenella: up to 22%); the content of digeneaside, exclusively found in species of the Ceramiales, is lower, in the range of 1–2.2% on a dry weight basis. All species investigated have Cl− as main anion, while there is a remarkable diversity in cation composition. Na+ was the major cation in 12 of the species investigated, the others having K+ as main cation.
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Radioisotope equilibration techniques have been used to determine the intracellular concentration of K+, Na+ and Cl−, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of 42K+, 24Na+ and 36C1− are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K+ and Cl− and against Na+. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K+ and Cl− influx and Na+ efflux. ‘Active’ uptake and ‘passive’ loss of K+ and Cl− are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K+ and Cl− may be due to ‘exchange diffusion’ (K+/K+ and Cl−/Cl−antiport).
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The effect of different nutrient media on growth, physicochemical, and agar properties of the marine algae Gracilaria cliftonii was investigated in ocean water (OW) and inland saline water (ISW). G. cliftonii fronds were cultured in 500-mL and 25-L containers with different nutrient media: Aquasol, Total, Guillard f2, Walnes, and Modified-Provasoli's Enriched Seawater in OW and ISW at 35 ppt. Specific growth rate (SGR) was higher in OW than ISW irrespective of nutrient media in both volumes. Growth of G. cliftonii in Guillard f2-supplemented OW was significantly higher than other nutrient media in both water types. Nutrient media had no influence on growth and agar properties. However, f2supplemented OW resulted in significantly higher agar yield (58.3% db) as compared to other media. Either f2 or Walnes media are preferred nutrient sources for culturing G. cliftonii in ocean and inland saline water.
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The red alga Polysiphonia urceolata (Rhodomelaceae, Ceramiales) shows a bromine requirement for optimal growth when cultivated in axenic culture. No influence of bromine on growth of Goniotrichum alsidii (Goniotrichaceae, Bangiales) was observed. Organically bound bromine (lanosol) could be utilized by Polysiphonia as a bromine source. Some correlation between iodide concentration and suitable bromide concentration in the medium was indicated.
Chapter
Im vorigen Band der „Fortschritte der Botanik“ berichtete Weigl über „Struktur und Funktion pflanzlicher Membranen“. Mein Referat ist eine spezielle Fortsetzung jenes Berichts, denn die Elektrophysiologie der Zellen stellt nur eine besondere Betrachtungsweise der Struktur und Funktion der Zellmembranen und Zellwände dar. Ziel der Elektrophysilogen ist es, die an der Zellwand, dem Plasmalemma und dem Tonoplasten meßbaren elektrischen Spannungen und ihre Veränderungen aus der Struktur und Funktion der Membranen, der Wand und aus den Ionenverhältnissen zu erklären. Von den weiteren Membranen der Zelle ist nur das endoplasmatische Reticulum in Form der doppelten Kernmenbran der elektrophysiologischen Forschung zugängig (Kroeger).
Chapter
The use of giant algal cells has been very important in recent advances in our understanding of the mechanism of solute and water transport in plants. This research has viewed giant algal cells as convenient material for the study of membrane properties per se; the involvement of solute transport in the life of the plant particularly with respect to nutrition, has been relatively neglected.
Article
Analysis of NaCl toxicity in Chlorella sorokiniana showed decreased growth rates, increased dry weight per cell, increased intracellular Na(+) and Cl(-), more total chlorophyll per cell, a decreased chlorophyll a to chlorophyll b ratio, increased rates of O(2) evolution, and decreased rates of CO(2) fixation when the extracellular concentration of NaCl was increased from zero to 0.3 m. Cultures did not grow at concentrations greater than 0.3 m NaCl unless 10 mm calcium salts were present. Inclusion of that concentration of Ca(2+) extended the tolerance to 0.5 m NaCl before growth stopped. Increasing the light intensity from 1.2 to 9.4 mw/cm(2) increased growth rates for cultures in 0.10 to 0.45 m NaCl. At 14 mw/cm(2) added Ca(2+) reduced growth rates of cultures in 0.3 m NaCl compared to controls without added Ca(2+). Maximal growth rates for cultures in NaCl media were achieved by addition of 10 mm CaSO(4) and maintenance of the light intensity at 9.4 mw/cm(2). The maximal growth rate of the organism was 9.6 doublings/day achieved at 2.7 mw/cm(2) for control cultures. In 0.3 m NaCl the growth rate was 4.3 doublings/day at 2.7 mw/cm(2) and 8.2 doublings/day at 9.4 mw/cm(2) with 10 mm CaSO(4) added.Increasing light intensities from 2.7 to 9.4 to 14 mw/cm(2) decreased intracellular Na(+) in cells cultured in 0.3 m NaCl medium without added Ca(2+) and increased Cl(-) uptake in cells cultured in 0.3 m NaCl medium with and without added Ca(2+). For cells cultured in 0.3 m NaCl medium at 14 mw/cm(2) intracellular Na(+) was 0.68 meq/g dry weight with Ca(2+) added and 0.81 meq/g dry weight without Ca(2+) added. Addition of Ca(2+) at 2.7 mw/cm(2) reduced intracellular Na(+) to similar values. It is postulated that energy requirements for active Na(+) exclusion were reduced by addition of Ca(2+) allowing more energy to be used for cell growth resulting in increased growth rates.O(2) evolution and CO(2) fixation studies indicated that increased photosynthetic energy, probably actuated by a high proton gradient accompanying Cl(-) influx and uncoupled from CO(2) fixation, was available for maintenance of cellular integrity and active control of intracellular ionic ratios. The O(2) evolving capacity was destroyed at 12 and 29 mw/cm(2) for cells cultured in 0.3 m NaCl medium respectively with and without the addition of Ca(2+). Control cultures continued producing O(2) at light intensities up to 115 mw/cm(2).
Article
SUMMARY The potential differences across the tonoplast and plasmalemma membranes have been measured in the single cells of Nitella translucens, the cells being immersed in an artificial pond water (composition: NaCl 1.0 mM., KC1 0.1 mM., CaCl2, 0.1 mM.). The potential of the cytoplasm is –138 m V with respect to the bathing medium and –18 mV with respect to the vacuole. The concentrations of Na, K, and Cl have been measured in the two cell fractions. The concentrations in the flowing cytoplasm are: Na 14 mM., K 119 mM., and Cl 65 mM.; the vacuolar concentrations are: Na 65 mM., K 75 mM.,and Cl 160 mM. The observed potential differences across the two membranes are compared with the Nernst potentials for all three ions. This analysis shows that all three ions are actively transported at the plasmalemma: Na is pumped outwards while K and Cl are pumped inwards. At the tonoplast Na is pumped into the vacuole while K and Cl are close to electrochemical equilibrium. The inhibitor, ouabain, has no effect on the cell resting potential.
Article
1. As much as 80 per cent of the water in intertidal marine algae is frozen when exposed to the low air temperatures that regularly occur in nature.2. The same species may lose 90 per cent of their water by ordinary drying during tidal exposure.3. Metabolism is greatly depressed in both the frozen and dried states.4. The ability to withstand drying may be related to freezing hardiness.5. Some extreme conditions in the Arctic are described. Fucus spends many months frozen into the sea ice at temperatures down to, 40° C., yet it is capable of photosynthesis immediately upon being thawed out.
Article
The ionic state of single internodal cells of a fresh water characean, Nitella translucens, has been studied. In mature cells the vacuolar concentrations were 78 mM K, 60 mM Na, and 151 mM Cl, compared with concentrations of 0.1 mM K, 1.0 mM Na, and 1.3 mM Cl in the bathing medium. The results suggest an active influx of potassium and an active efflux of sodium at the plasmalemma, and an active influx of chloride, probably at the tonoplast. The cation transport is inhibited by ouabain, and is more efficient in young cells; the chloride transport is insensitive to ouabain, and unaffected by age. Thus the two systems appear to be independent. It is suggested that the active fluxes are 0.5 to 0.6 micromicromoles K/cm(2) sec. inwards, and 0.45 micromicromoles Na/cm(2) sec. outwards. The passive influxes, 0.3 micromicromoles K/cm(2) sec. and 0.55 micromicromoles Na/cm(2)sec., give a value for the relative permeabilities of the plasmalemma, P(Na)/P(K), of 0.18. The absolute magnitudes of the permeabilities, compared with those derived from resistance measurements, suggest that potassium ions interact strongly in the membrane. The cation fluxes at the tonoplast are much higher than those at the plasmalemma. The active influx of chloride is 0.85 micromicromoles/cm(2) sec. in light, but only 0.052 micromicromoles/cm(2) sec. in the dark. The potassium influx is also reduced in the dark. Thus the energy for both active transport processes is closely geared to light-dependent metabolism, rather than to respiration.
Article
1. The methods employed in these and preceding (25–27) studies were shown to allow analysis of true cellular sodium and potassium concentrations. 2. The rate of reaccumulation of potassium by potassium-deficient cells is independent of the presence or absence of sodium in the external medium. 3. Phenylurethane (10–3 M), a photosynthetic and metabolic inhibitor, causes a marked progressive loss of potassium and gain of sodium, both of which changes are completely reversible on transferring the samples to running sea water. 4. Iodoacetate, while not effective in causing potassium and sodium shifts in the light, effects a loss of potassium and a gain of sodium in the light in the presence of phenylurethane. 5. Arsenate (5 x 10–3 M) completely protects Ulva against the potassium loss usually observed with iodoacetate in the dark while it affords no protection against the sodium influx under the same conditions. Arsenate given after 18 to 20 hours in iodoacetate gives significant protection against potassium loss in the dark, and allows a slight net reaccumulation of potassium in the light. Arsenate in the dark after iodoacetate affords no protection against the sodium uptake caused by iodoacetate in the dark, while in the light under the same conditions sodium is rapidly secreted to the control level within a few hours. This resecretion of sodium is thought to be primarily an effect of light, the presence of arsenate being incidental. 6. The "decoupling agent" 4,6-dinitro-o-cresol causes a marked progressive increase in cellular sodium and a drop in cellular potassium, though the kinetics of these two movements are distinctly different from each other. 7. Pyruvate (50 mg. per cent) given with iodoacetate (2 x 10–3 M) for 5 hours in the dark completely prevents the sodium increase caused by iodoacetate, while affording less protection against the potassium loss. Phosphoglycerate, on the other hand, offers more protection against potassium loss, and essentially none against the sodium gain. 8. ATP added in small amounts at short intervals to samples maintained in 10–3 M iodoacetate in the dark affords significant protection against the potassium loss observed in iodoacetate. Cellular sodium is somewhat higher in the ATP-iodoacetate samples than in the iodoacetate samples. 9. In the discussion of the data presented two major points are emphasized: (1) the close correlation between cellular metabolism and normal cation control; (2) two mechanisms must be operative in cation regulation in this organism: one for moving potassium inwards and the other for transporting sodium outwards. These mechanisms are independent of each other.
Article
Cells of the red marine alga, Porphyra perforata, accumulate potassium and exclude sodium, chloride, and calcium. Various metabolic inhibitors including dinitrophenol, anoxia, and p-chloromercuribenzoate partially abolish the cells' ability to retain potassium and exclude sodium. Iodoacetate induces potassium loss only in the dark; reduced sulfur compounds offer protection against the effects of p-chloromercuribenzoate; dinitrophenol stimulates respiration at concentrations which cause potassium loss and sodium gain. Following exposure to anoxia potassium accumulation and sodium extrusion take place against concentration gradients. These movements are retarded by sodium cyanide, but are stimulated by light. Sodium entry, following long exposure to 0.6 M sucrose, occurs rapidly with the concentration gradient, while potassium entry against the concentration gradient takes place slowly, and is prevented by cyanide.
Article
The distribution and rates of exchange of the ions sodium, potassium, and chloride in single internodal cells of the ecorticate characean, Nitellopsis obtusa, have been studied. In tracer experiments three kinetic compartments were found, the outermost "free space" of the cell, a compartment we have called "protoplasmic non-free space", and the cell sap. The concentrations in the vacuole were 54 mM Na+, 113 mM K+, and 206 mM Cl-. The steady state fluxes across the vacuolar membrane were 0.4 pmole Na+/cm.2 sec., 0.25 pmole K+/cm.2 sec., and 0.5 pmole Cl-/cm.2 sec. The protoplasmic Na/K ratio is equal to that in the vacuole but protoplasmic chloride is relatively much lower. Osmotic considerations suggest a layer 4 to 6 µ thick with sodium and potassium concentrations close to those in the vacuole. The fluxes between protoplasm and external solution were of the order of 8 pmoles Na+/cm.2 sec. and 4 pmoles K+/cm.2 sec. We suggest that the protoplasm is separated from the cell wall by an outer protoplasmic membrane at which an outward sodium transport maintains the high K/Na ratio of the cell interior, and from the vacuole by the tonoplast at which an inward chloride transport maintains the high vacuolar chloride. The tonoplast appears to be the site of the principal diffusion resistance of the cell, but the outer protoplasmic membrane probably of the main part of the potential.
Article
Potassium-free artificial sea water causes a loss of cell potassium and a gain of cell sodium in Porphyra perforata, which is not attributable to an inhibition of respiration. On adding KCl or RbCl to such low potassium, high sodium tissues, net accumulation of potassium or rubidium takes place, accompanied by net extrusion of sodium. Rates of potassium or rubidium accumulation and sodium extrusion are proportional to the amount of KCl or RbCl added only at low concentrations. Saturation of rates is evident at KCl or RbCl concentrations above 20–30 mM, suggesting the role of an ion carrier mechanism of transport. Evidence for and against mutually dependent sodium extrusion and potassium or rubidium accumulation is discussed.
Article
The active transports of sodium and chloride ions, between the vacuole and environmental solutions, were measured in the giant coenocyte of the marine alga Halicystis ovalis. Ion fluxes, determined isotopically, of individual single cells were measured by the short-circuit technique of Ussing and Zerahn (1951). Concentric pipettes were used to replace the vacuole sap with sep water and to short-circuit the vacuole potential difference to zero. The mean net efflux of sodium represented 39.2%, S. D. = 5.4, and the mean net influx of chloride 57.6%, S. D. = 5.3, of the current flowing through a short-circuited cell. Therefore a summation of the current carried by the two net active fluxes can account for the total short-circuit current. Micro-electrode penetration of the protoplasm of the cell indicated that the potential difference of the protoplasm was identical with the vacuole potential; that the total potential difference develops at the outer membrane. A theory is presented which evaluates the effect of these transport systems on the total potential difference and on the osmotic stability of the cell relative to its environment.
Article
Cells of Porphyra perforata, a red marine alga, accumulate K in the absence of concomitant Na or Li extrusion while immersed in Li- or Mg-sea waters lacking Na. This suggests that the coupling observed between K and Na transport is facultative. No evidence is obtained for net extrusion of Li. Na efflux, with the concentration gradient, is facilitated by K and is proportional to the cellular Na content. Either Na efflux does not involve an ion carrier or the number of Na sites is large. Because K accumulation has been observed in the absence of Na extrusion, but not vice versa, it seems that K uptake is the primary secretory event, with Na extrusion a secondary process dependent upon K accumulation.
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1.1. The aim of the work was to decide whether the link between light and the light-driven active ion fluxes in Nitella translucens reflects the consumption of ATP produced by photophosphorylation in the process of ion transport, or is the consequence of a direct coupling between ion transport and photosynthetic electron-transfer reactions.2.2. The active uptake of Cl− appears to require the participation of the second light reaction of photosynthesis—that involving the photooxidation of water, for which Cl− is an essential cofactor. Thus the Cl− uptake is not supported by far-red light in which only cyclic photophosphorylation is possible, and is sensitive to low concentrations of dichlorophenyldimethylurea.3.3. By contrast the active uptake of K+ can be supported by cyclic photophosphorylation alone, in far-red light or in the presence of low concentrations of dichlorophenyldimethylurea.4.4. Low concentrations of imidazole, which uncouples photophosphorylation in isolated chloroplasts, inhibit K+ uptake while leaving the Cl− flux unaffected.5.5. It is suggested that K+ uptake is supported by light energy through the utilization of ATP produced in photophosphorylation, but that the Cl− uptake is directly linked to the light-driven electron-transfer reactions associated with the evolution of O2 in photosynthesis, and does not depend on photophosphorylation.6.6. This work provides further evidence for the occurrence of cyclic photophosphorylation in intact cells.