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1

Digitale Medien

Acid-base regulation during ammonium assimilation in Hydrodictyon africanum (1980)

RAVEN, J. A. ; MICHELIS, M. I.

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 3 (1980), S. 0

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ISSN: 1365-3040

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: Abstract The acid-base balance during ammonium (used to mean NH 4+ and/or NH3) assimilation in Hydrodictyon africanum has been measured on cells growing with about 1 mol m−3 ammonium at an external pH of about 6.5. Measurements made included (1) ash alkalinity (corrected for intracellular ammonium) which yields net organic negative charge, (2) the accumulation of organic N in the cells and (3) the change in extracellular H+ (from the pH change and the buffer capacity). These measurements showed that some 0.25 excess organic negative charge (half in the cell wall, half inside the plasmalemma) accumulates per organic N synthesized, while some 1.25H+ accumulate in the medium per organic N synthesized. Granted a permeability (PNH3) of some 10−3 cm s−1, and a finite [NH3] in the cytoplasm of these N-assimilating cells it is likely that most of the ammonium entering these growing cells is as NH 4+. This means that most of the H + appearing in the medium must have originated from inside the cell and have been subjected to active efflux at the plasmalemma: H+ accumulates in the medium equivalent to any NH3 entry by requilibration from exogenous NH 4+. The cell composition (net organic negative charge, organic N content) is very similar in these ammonium-grown cells to that of NO3+grown cells, suggesting that there is no action of a ‘biochemical pH stat’ during longterm assimilation of NO3+in H. africanum.Short-term experiments were carried out at an external pH of 7.2 in which ammonium at various concentrations were supplied to NO3+-grown cells. There was in all cases a rapid influx followed by a slower uptake; at least at the lower concentrations (less than 100 μmol dm−3) the net influx was all attributable to NH4+influx via a uniporter, probably partly short-circuited by a passive NH3 efflux due to intrinsic membrane permeability to NH3. The net ammonium influx was in all cases associated with H+ accumulation in the medium. (1.3-1.7 H + per ammonium taken up); as in the growth experiments, most of the ammonium taken up was assimilated.Determinations of cytoplasmic pH showed either no effect on, or a slight decrease in, pH during ammonium assimilation; the changes that occurred were in the direction expected for actuating a ‘pH-regulating’ change in H+ fluxes.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/1365-3040.ep11581869

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2

Digitale Medien

Source—sink characteristics of carbon transport in Chara hispida (1984)

ANDREWS, M. ; BOX, R. ; FYSON, A. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Plant, cell & environment 7 (1984), S. 0

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ISSN: 1365-3040

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: Abstract Rates of uptake of 14C-labelled inorganic carbon were measured for whole Chara hispida plants, detached parts of the shoot and isolated (split-chamber technique) apices, lateral branchlets and rhizoid—node complexes.The rates of inorganic carbon uptake by the rhizoid—node complex expressed per gram fresh weight whole plant were three to four orders of magnitude less than the uptake for the whole plant. Up to 70% of the carbon taken up by the rhizoid—node complex was translocated to the shoot. After 12 h exposure to 14C-labelled inorganic carbon the concentration of 14C was greater in apices than in uppermost or central internodal cells and in all lateral branchlets, regardless of whether label was supplied to the whole plant or isolated rhizoid—node complexes. Measurement of inorganic carbon uptake by detached internodal cells and detached and isolated apices and lateral branchlets showed that lateral branchlets had the greatest rates of inorganic carbon uptake. During 12 h exposure to 14C, isolated lateral branchlets translocated to the attached shoot 55% of the labelled carbon taken up; for isolated apices this value was only 13%.It is concluded that it is highly unlikely that the rhizoid of Chara hispida could acquire a significant fraction of the whole plant requirement for inorganic carbon and that apices are sink regions for photosynthate while lateral branchlets are source regions.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/1365-3040.ep11572119

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3

Digitale Medien

BIOLOGY OF NONVASCULAR PLANTS (Book). (1984)

Raven, J. A.

Oxford, UK : Blackwell Publishing

Plant, cell & environment 7 (1984), S. 0

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ISSN: 1365-3040

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/1365-3040.ep11589483

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4

Digitale Medien

Inhibitor effects on photosynthesis, respiration and active ion transport inHydrodictyon africanum (1971)

Raven, J. A.

Springer

The journal of membrane biology 6 (1971), S. 89-107

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ISSN: 1432-1424

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Chemie und Pharmazie

Notizen: Summary The effects of various inhibitors on photosynthesis, respiration, and active influx of K and Cl in light and dark inHydrodictyon africanum is reported. The inhibitors used were arsenate (uncouples electron-transport phosphorylations), dicyclohexylcarbodiimide (energy-transfer inhibitor in electron-transport phosphorylation), quinacrine (uncouples photophosphorylation and inhibits oxidative phosphorylation), and ethionine (traps adenylates as S-adenosyl ethionine). The action of these inhibitors, and of those previously used onHydrodictyon africanum, suggests that K influx requires ATP, while Cl influx requires some earlier manifestation of the ATP synthesizing process. Possible reasons for the greater sensitivity of K influx than of CO2 fixation to treatments which interfere with photophosphorylation are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01873457

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5

Digitale Medien

Ouabain-insensitive K influx in Hydrodictyon africanum (1971)

Raven, J. A.

Springer

Planta 97 (1971), S. 28-38

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ISSN: 1432-2048

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary The occurrence is reported of cells of Hydrodictyon africanum which have, contrary to previous reports by the author, a K influx which is almost insensitive to ouabain. The conditions which govern the ouabain-sensitivity of the K influx have not yet been defined. The low ouabain sensitivity of the total K influx seems to be related to a smaller than usual activity of the component of K influx which is linked to Na efflux, and also to a smaller sensitivity of this component to inhibition by ouabain. The major components of K influx in ouabain-insensitive cells correspond to those components previously described as the passive and Cl-linked components. The occurrence is also reported of an increased sensitivity of active Cl influx (and the coupled cation influxes) in the light to uncouplers when the medium is aerated or otherwise stirred.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00388403

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6

Digitale Medien

Inorganic carbon assimilation in the Isoetids, Isoetes lacustris L. and Lobelia dortmanna L. (1984)

Richardson, K. ; Griffiths, H. ; Reed, M. L. ; [weitere]

Springer

Oecologia 61 (1984), S. 115-121

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ISSN: 1432-1939

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary The inorganic carbon fixation patterns of Isoetes lacustris and Lobelia dortmanna from an oligotrophic Scottish loch have been examined by following titratable acidity changes in plant sap and light/dark 14CO2 incorporation by roots and shoots. The diurnal pattern of titratable acidity changes in I. lacustris suggests crassulacean acid metabolism (CAM) while the lack of any change in titratable acidity in L. dortmanna suggests C3 metabolism. Of the carbon fixed by L. dortmanna, 99.9% was taken up through the roots and fixation occurred primarily during the day. In Isoetes, CO2 was taken up by both roots and shoots and during both day and night. Regardless of the site of CO2 uptake, fixation occurred only in the shoots of both plants. Analysis of carbon isotope ratios of plant organic material was used to further investigate the photosynthetic mechanisms of these Isoetids. Considering the absence of a nighttime peak in titratable acidity in L. dortmanna, the Δ13C (Δ=δ13C plant-δ13C source) value of the shoots of L. dortmanna (-14.2‰) is indicative of C3 photosynthesis limited by the rate of CO2 diffusion. The less negative Δ of I. lacustris (-6.0‰) is consistent with both dark acidification of CAM and CO2 limited C3 photosynthesis. This is in contrast to the terrestrial Isoetes durieui which is shown to have a Δ value which is similar to a terrestrial C3 plant. The carbon fixation patterns of these Isoetids suggest that the CO2 concentration in the loch may be growth limiting, and that root uptake and/or dark acidification are means of optimising CO2 supply. However, in view of the relatively high levels of CO2 in sediment and bulk water, it is suggested that low levels of nutrients may also limit growth in these plants.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00379096

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