STUDIES OF NITRATE TRANSPORT BY MARINE PHYTOPLANKTON USING 36Cl-ClO3− AS A TRANSPORT ANALOGUE. I. PHYSIOLOGICAL FINDINGS1 |
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Authors: | William M Balch |
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Institution: | Institute of Marine Resources, A-018 Scripps Institution of Oceanography, La Jolla, California 92093 |
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Abstract: | Transport of a nitrate analogue, 36Cl-ClO3−, was examined in two diatoms, Skeletonema costatum (Greve.) Cleve and Nitzschia closterium (Ehrenb) W. Sm. A dinoflagellate, Gonyaulax polyedra did not transport ClO3−. Transport of 36Cl-ClO3− by diatoms appeared to be active and showed saturation kinetics. The data were fitted by Michaelis-Menten equation at all but the lowest chlorate concentrations (where plots of S vs. v showed a slight concave bend). Affinity of cells for nitrate was considerably higher than for chlorate. The Ki for nitrate inhibition of chlorate transport was calculated assuming competitive inhibition. Light had little or no effect on chlorate transport. Pulse-chase experiments demonstrated that (1) ClO3− (hence NO3−) was stored in two intracellular compartments of equal size, (2) internal ClO3− was exchangeable with external ClO3− (rates of efflux and influx were measured), and (3) efflux of intracellular ClO3− showed transient states following a chase of ClO3− or NO3− which stabilized after 10–20 min. Transport of chlorate was a function of growth phase. |
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Keywords: | 36Cl-chlorate Gonyaulax polyedra Stein internal pools nitrate transport Nitzschia closterium (Ehrenb) W Sm nutrient analogue Skeletonema costatum (Greve ) Cleve |
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