Role of silicon in diatom metabolism

Azam, Farooq; Hemmingsen, Barbara B.; Volcani, Benjamin E.

doi:10.1007/bf00403050

Cited by 103 publications

(29 citation statements)

References 19 publications

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“…But biological research on silicon is difficult, and what is known of its metabolic role has been gained from diatom studies. Diatoms use the silicate ion for wall formation (2), DNA replication (3,4), nuclear DNA polymerase (5) and thymidylate kinase (4) synthesis, and cyclic AMP and cyclic GMP formation (6); hence diatoms possess specific active silicate transport system(s) (7)(8)(9)(10). But little is known of how energy is coupled to silicate transport or of the energy-conserving processes in diatoms.…”

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“…Cells were incubated in a water bath at 30'C with stirring; uptake was started by adding 31Si from a 3 mM potassium [3lSi]silicate stock, specific activity ca. 1 Ci/10 mol (1 Ci = 3.7 X 1010 becquerels), prepared as described (7). Samples (0.5 ml) were removed at intervals, filtered through 1.2-/Am Millipore HA filters, and immediately washed with two successive 5-ml portions of unlabeled medium and assayed for radioactivity in a liquid scintillation counter.…”

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Sodium-dependent silicate transport in the apochlorotic marine diatom Nitzschia alba

Bhattacharyya

Volcani

1980

Proc. Natl. Acad. Sci. U.S.A.

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Silicate uptake by Nitzschia alba cells is higher in medium containing Na+ than in media lacking Na+ but containing K+, Rb+, NH4W, Li+, or choline+. The initial rate is inhibited by monensin and gramicidmi but not by valinomycin or nigericin and is less sensitive to inhibition by carbonyl cyanide m-chlorophenylhydrazone (CCCP). In isolated membrane vesicles, silicate is taken up when a Na+ gradient is imposed across the membrane or is generated by cytoplasmic Na4,K+-ATPase. H+ or K+ gradients in either direction do not stimulate uptake. Na+-gradient-dependent uptake is inhibited by monensin but not by CCCP, valinomycin, or vanadate, which inhibits the cytoplasmic Nav+a+-ATPase. Uptake increases if an internally negative potential is imposed across the membrane. The vesicular uptake shows saturation kinetics with a Km of 62 jiM and a Vmax of 4.1 nmol/mg of protein per min. In intact cells, the initial rate of silicate uptake increases with pH up to 9.5. Thus, in N. alba, silicate is symported with Na+, and the transport system is driven by the Na+ gradient that is generated and maintained across the membrane by the activity of Na+,K+-ATPase.Silicon is an essential trace element for basic processes ranging from DNA synthesis to bone formation, and in mammalian systems it acts as both a metabolite and a cytotoxic factor (1). But biological research on silicon is difficult, and what is known of its metabolic role has been gained from diatom studies. Diatoms use the silicate ion for wall formation (2), DNA replication (3, 4), nuclear DNA polymerase (5) and thymidylate kinase (4) synthesis, and cyclic AMP and cyclic GMP formation (6); hence diatoms possess specific active silicate transport system(s) (7-10). But little is known of how energy is coupled to silicate transport or of the energy-conserving processes in diatoms. Mitchell's chemosmotic theory of energy conservation in the form of ion gradients has proven to be true in various organisms (11)(12)(13)(14). In eukaryotic mammalian cells, the Na+ gradient, generated and maintained by plasma membranebound Na+,K+-ATPase, is coupled to most transport systems (15)(16)(17). Diatoms also possess a Na+,K+-ATPase in the plasma membrane, though it differs from the mammalian ATPase in many properties (18). Whether this enzyme or other energyyielding processes in the diatoms generate ion gradients has not been examined.In the fresh water diatom Nadculla pelliuulosa, Na+ is somewhat effective in promoting silicate uptake, K+ is half as effective as Na+, and NH+ and Li+ are ineffective (9). Glucose and amino acid transport systems in the marine diatom Cyclotella cryptica were found to be Na+ dependent (19), though it was suggested that the Na+ dependence may also be caused by the indirect effect of Na+ on the energy metabolism. On the The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 6386other hand, K+-depend...

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confidence: 99%

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confidence: 99%

Sodium-dependent silicate transport in the apochlorotic marine diatom Nitzschia alba

Bhattacharyya

Volcani

1980

Proc. Natl. Acad. Sci. U.S.A.

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“…Earlier physiological and biochemical studies focused on Phaeodactylum tricornutum [20,21], Cylindrotheca fusiformis [22,23], Nitzschia alba [24][25][26], and Navicula pelliculosa [27,28]. C. fusiformis in particular has been extensively studied, in part because of the ability to grow cultures of this diatom synchronously [29].…”

Section: Diatoms As Model Organisms To Study Biosilicificationmentioning

confidence: 99%

“…Chemical determination [60] and NMR [61] indicate that the pools consist of either mono-or poly-silicic acid, and extraction experiments suggest that it was complexed with as yet uncharacterized organic molecules [24,62]. Certain aliphatic polyols can form penta-or hexa-coordinate complexes with silicic acid [63], however, NMR measurements indicated that the vast majority of diatom intracellular silicon was mono-silicic acid, and a very slight signal for multicoordinate complexation occurred only after an extended time period in the dark [61], which is not relevant with regards to the timing of intracellular pool fluxes [48].…”

Section: Equilibrium Factors Involved In Diatom Silicon Transportmentioning

confidence: 99%

“…Early studies monitoring silicon uptake in diatoms indicated that the process was saturable, and hence carrier-mediated [24,66,67]. Numerous studies have reported Michaelis-Menten type saturation kinetics of Si OH 4 uptake in diatoms, but occasionally nonsaturable or biphasic kinetics were observed [68][69][70].…”

Section: Identification and Characterization Of Silicon Transportersmentioning

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