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THE KINETICS OF PENETRATION : XIV. THE PENETRATION OF IODIDE INTO VALONIA
1Laboratories of The Rockefeller Institute for Medical Research, New York, and The Bermuda Biological Station for Research, Inc., Bermuda.
The Journal of General Physiology
|October 30, 2009
Summary
Sodium iodide (NaI) readily enters the Valonia alga because its external concentration drives passive transport. This contrasts with other substances, highlighting unique cellular permeability to iodide.
Area of Science:
- Cell Physiology
- Membrane Transport
- Plant Biology
Background:
- Investigating the entry mechanisms of ions into plant cells.
- Understanding the differential permeability of cell membranes to various solutes.
Purpose of the Study:
- To determine how sodium iodide (NaI) enters the Valonia alga.
- To compare iodide transport with that of other substances like sulfide and carbon dioxide.
- To elucidate the factors influencing the rate of iodide uptake.
Main Methods:
- Addition of 0.1 M NaI to the external seawater surrounding Valonia.
- Observation of iodide presence in the algal sap.
- Analysis of transport rates under varying external pH conditions.
Main Results:
- Iodide enters Valonia sap primarily as NaI, with negligible entry as HI.
- The rate of NaI entry is independent of external pH, indicating passive diffusion.
- NaI uptake is proportional to external concentration and is faster at lower concentrations.
- Protoplasmic passage of NaI is significantly slower than through water, suggesting a barrier in non-aqueous surface layers.
Conclusions:
- Valonia exhibits selective permeability, with NaI entering via passive transport driven by external concentration gradients.
- Cellular permeability to NaI differs significantly from that of H2S and CO2, which enter in their undissociated forms.
- The rate of iodide entry is primarily governed by external NaI concentration and is hindered by the cell's non-aqueous surface layers.
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