ISSN:
1432-072X
Keywords:
Diatom
;
Nitzchia alba
;
Silicic Acid
;
Transport
;
Metabolism
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract 1. In the heterotrophic diatom, Nitzschia alba, 31Si(OH)4 appears to be transported by a carrier-mediated membrane transport system which conforms to Michaelis-Menten type saturation kinetics with a K s of 4.5×10-6M and a V max of 3.35 gmmoles/g wet wt/min at 30°C. A Q10 of 2.0 was calculated from rates of silicic acid uptake at 20°C and 30°C. Calculations from the same data showed that energy of activation for uptake is 12.1 Kcal/mole. Optimum pH for transport is broad, ranging between 6 and 9. 2. During pulse-labelling with 31Si(OH)4, the label increases in the cytoplasm more rapidly than in the cell wall, indicating the build-up of a cytoplasmic pool of silicic acid or its derivatives, and suggesting a possible chemical transformation of silicic acid in the cytoplasm. The concentration of 31Si in the cytoplasm reaches 30 to 40 times the external concentration, but the accumulated 31Si does not flow out into a Si-free medium or exchange with non-radioative Si(OH)4. 3. The metabolic inhibitors DNP, CCCP, iodoacetamide, azide, and antimycin A strongly inhibit the uptake of silicic acid by 90–97%, whereas the ionophorous compounds, nigericin and valinomycin, have no effect. 4. Inhibition of protein synthesis with cycloheximide inhibits silicic acid uptake by 50–70%. 5. Germanic acid, an inhibitor of diatom growth, inhibits silicic acid uptake; the K i is 2.2×10-6. 6. Sub-cellular fractionation of cells exposed to 31Si(OH)4 for 10 min showed that 90% of the label is in the cell wall; the remaining 10% is distributed in various cytoplasmic fractions including the “soluble fraction”. 7. The data demonstrate that metabolic energy is required for net uptake of silicic acid by N. alba cells, and suggest that an active transport system may be involved. The possible role and nature of the silicic acid pool are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00403050
