Ammonium uptake by phytoplankton cells on a filter: a new high-resolution technique

Parslow, J. L. F.; Harrison, P J; Thompson, Peter A.

doi:10.3354/meps025121

Cited by 12 publications

(13 citation statements)

References 10 publications

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“…1976, Rhee past history and constant uptake intervals 1978). Parslow et al (1985a) have shown that feedback may occur on a scale of seconds (not minutes) but it is difficult to resolve uptake on this time scale with the AutoAnalyzer@. Probably the best way to estimate feedback inhibition is to determine an inhibition constant (Rhee 1974).…”

Section: Non-linear Disappearance Of Limiting Nutrientmentioning

confidence: 99%

Determination of nutrient uptake kinetic parameters: a comparison of methods

Harrison¹,

Parslow²,

Conway³

1989

Mar. Ecol. Prog. Ser.

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165

132

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Three methods which have been used to determine nutrient uptake hnetic parameters were compared using steady-state NH,-limited cultures of the chrysophyte Pseudopedinella pyriforrnis. The first 2 methods involved a multiple flask incubation where different concentrations of substrate were added to each flask. Method 1 used a variable incubation time, while the incubation time of Method 2 was short and constant. The third method, the perturbation method, involved one large addition of the substrate to one culture and hence the nutritional past history varied throughout the experiment. This method was used also with the diatoms Skeletonema costatum and Chaetoceros debilis in Si-Limited chemostats. Results inhcate that, for nutrient-limited cultures, kinetic parameters are best estimated using multiple additions of the substrate and a short constant incubation time (Method 2). It appears that this method determines membrane transport, which is still not completely free of feedback inhibition even when the incubation time is very short (e.g. 2 min). The short incubation time is necessary because the maximal uptake velocity (V,) decreases with increasing incubation time especially for phosphate and ammonium. Method 3 provides valuable information on a third parameter, V,, the approximate assimilation rate of the limiting nutrient, that is not obtained by the other methods. Multlple sequential additions of the limiting nutrient to N-or Si-limited Skeletonema costaturn and Chaetoceros debilis revealed that if the additions were small (e.g. 2 pM NH,), there was no change in subsequently determined nutrient uptake kinetic parameters. If the sequential additions were larger (e.g. 6 PM) then the maximal uptake rate slowed with time.

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Section: Non-linear Disappearance Of Limiting Nutrientmentioning

confidence: 99%

Determination of nutrient uptake kinetic parameters: a comparison of methods

Harrison¹,

Parslow²,

Conway³

1989

Mar. Ecol. Prog. Ser.

Self Cite

165

132

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“…In the reduction experiments, FeEDTA (10 M Fe : 100 M EDTA) was added to the SOW. Subsamples from the sample line were then automatically injected into the carrier solution (18.2 M⍀ MilliQ-water), mixed with the luminol reagent [0.1 mM 5-amino-2,3-dihydro-1,4-phthalazinedione (Luminol, Sigma Chemical) in NH 3 buffer solution (ഠ1 M, pH 11.8)], and introduced into the luminescence flow cell every min for up to 4 h. Cellular reduction rates were calculated from the steady-state Fe(II) concentration, the flow rate in the sample line, and the number of cells on the filter (e.g., Parslow et al 1985). …”

Section: Direct Determination Of Biologically Produced Fe(ii)-mentioning

confidence: 99%

Nitrate regulation of Fe reduction and transport by Fe‐limited Thalassiosira oceanica

Maldonado

Price

2000

Limnology & Oceanography

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Under Fe-limiting conditions, nitrate (NO 3 Ϫ )-grown marine diatoms have higher intracellular Fe requirements, but divide as fast or faster than ammonium (NH 4 ϩ )-grown cells by maintaining faster steady-state Fe uptake rates. Here we report that Thalassiosira oceanica, clone 1003, possesses an Fe reductase that reduces Fe(III) bound to a variety of organic ligands, including the siderophore desferrioxamine B (DFB), a high affinity, Fe(III)-specific ligand. Reduction is mediated extracellularly and is induced by Fe deficiency. Cellular rates of Fe(III) reduction are significantly faster in NO 3 Ϫ -than in NH 4 ϩ -grown cultures suggesting a link with N metabolism. At subsaturating Fe concentrations, short-and long-term Fe uptake rates are also significantly faster in NO 3 Ϫ -than in NH 4 ϩ -grown cells. The results suggest that when Fe is limiting, faster rates of reduction of organically bound Fe(III) by phytoplankton promote faster rates of Fe transport and growth. The implications of these findings could be significant for understanding phytoplankton Fe nutrition in oceanic waters where organic complexation dominates the speciation of Fe. We hypothesize that the reductive Fe transport pathway may enable phytoplankton to directly utilize Fe bound to strong organic ligands in the sea.Iron plays a catalytic role in many biochemical reactions as a cofactor of enzymes and proteins involved in chlorophyll synthesis, detoxification of reactive oxygen species, respiratory and photosynthetic electron transport, and N assimilation. Changes in the activity of these reactions or their replacement by functionally equivalent Fe-deficient pathways can greatly influence cellular Fe requirements of organisms. Because the NO 3 Ϫ assimilatory pathway is highly Fe dependent, utilization of NO 3 Ϫ by marine centric diatoms (Thalassiosira spp.) imparts a higher metabolic demand for Fe than the use of NH 4 ϩ . The demand for Fe is such that the Fe quotas (Fe : C) of NO 3 Ϫ -grown cells are 1.8 times higher than those of phytoplankton using NH 4 ϩ (Maldonado and Price 1996). Despite the higher Fe requirement for NO 3 Ϫ assimilation, under moderately Fe-limiting conditions (ca. 0.7-0.85 / max ), growth rates of NO 3 Ϫ -amended cultures are not slower than those of NH 4 ϩ -amended ones (Maldonado and Price 1996). Nitrate-grown cells apparently compensate for their extra Fe requirement by sustaining faster steadystate Fe uptake rates (Maldonado and Price 1996). The 1 To whom correspondence should be addressed. Present address: 5741 Libby Hall, School of Marine Sciences, University of Maine, Orono, ME 04469 (maria.maldonado@maine.edu). AcknowledgmentsWe thank P. Tortell, C. Payne, Z. Chase, and J. Granger for valuable discussions, suggestions, and comments on earlier versions of this manuscript. The help of E. Maldonado-Pareja and C. Molony in the lab was particularly appreciated. We are grateful to M. Soon (U. of British Columbia) for CHN analysis, to W. King (Colby College, ME) for guidance with the Fe(II) chemiluminescence ...

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“…la), following an ammonium pulse, has been suggested to be the result of filling an internal pool (Parslow et al 1985;Dortch et al 1984). The amount of nitrogen taken up per cell (0.3 1 pg-atom cell-') during a 3-min pulse would result in an average internal ammonium concentration of 37 mM (assuming a cell volume of 25 pm3, Table 1).…”

Section: Resultsmentioning

confidence: 99%

Coupling between ammonium uptake and incorporation in a marine diatom: Experiments with the short‐lived radioisotope ¹³N

Zehr

Falkowski

Fowler

et al. 1988

Limnology & Oceanography

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The coupling between ammonium transport and incorporation in the neritic marine diatom Thalassiosira pseudonana (3H) was investigated with the short-lived radioisotope 13N (& = 9.96 min). In ammonium-limited continuous cultures, growing at rates from 0.2 to 3.2 d-l, no trend in uptake rates per ccl1 was apparent, but the rate of incorporation of radiolabeled ammonium into trichloroacetic acid (TCA)-insoluble material, following a saturating pulse of ammonium, was linearly correlated with growth rate (r2 = 0.93). Calculated growth rates overestimated the measured rates. The ratio of calculated growth requirements (&) to growth requirements based on incorporation of 13N into TCA-insoluble material (pq) was nonlinearly related to growth rate. The discrepancy between & and pq was explained by isotope dilution in the internal free amino acid pool. The ratio of uptake to incorporation, corrected for isotope dilution in the amino acid pool, showed that uptake and growth were uncoupled at low growth rates but were coupled at P~,,~~. The ratio of short-term uptake to incorporation was found to be a direct measure of enhanced uptake and decreased with increasing growth rate. This ratio may be a useful parameter for determining growth rates and nitrogen deficiency in natural phytoplankton communities.Since the availability of fixed inorganic nitrogen is assumed to be a major factor regulating the abundance and growth rates of marine phytoplankton (Ketchum et al. 1958; Ryther and Dunstan 197 1;Thomas 1969Thomas , 1970 Thomas and Dodson 1972), kinetics of nitrogen uptake by marine phytoplankton have provided the focus of many investigations.Dugdale (1967) related nitrogen uptake rates to the external concentration of nitrogen by the Michaelis-Menten equation, V = V,,,[SI(K, + S)], where V is the uptake rate of the nitrogen substrate at Acknowledgments

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Ammonium uptake by phytoplankton cells on a filter: a new high-resolution technique

Cited by 12 publications

References 10 publications

Determination of nutrient uptake kinetic parameters: a comparison of methods

Determination of nutrient uptake kinetic parameters: a comparison of methods

Nitrate regulation of Fe reduction and transport by Fe‐limited Thalassiosira oceanica

Coupling between ammonium uptake and incorporation in a marine diatom: Experiments with the short‐lived radioisotope ¹³N

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Ammonium uptake by phytoplankton cells on a filter: a new high-resolution technique

Cited by 12 publications

References 10 publications

Determination of nutrient uptake kinetic parameters: a comparison of methods

Determination of nutrient uptake kinetic parameters: a comparison of methods

Nitrate regulation of Fe reduction and transport by Fe‐limited Thalassiosira oceanica

Coupling between ammonium uptake and incorporation in a marine diatom: Experiments with the short‐lived radioisotope 13N

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Product

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Coupling between ammonium uptake and incorporation in a marine diatom: Experiments with the short‐lived radioisotope ¹³N