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Osmoregulation by Oat Coleoptile Protoplasts (Effect of Auxin)
C. P. Keller1, E. Van Volkenburgh
1Department of Botany, Box 351330, University of Washington, Seattle, Washington 98195.
Plant Physiology
|March 1, 1996
Summary
Auxin (indoleacetic acid) promotes swelling in oat protoplasts by increasing potassium ion (K+) permeability of the plasma membrane. This auxin-induced swelling is K+-dependent and influenced by glucose concentration.
Area of Science:
- Plant Physiology
- Molecular Biology
- Biochemistry
Background:
- Plant protoplasts are valuable models for studying cellular transport and membrane dynamics.
- Auxins, like indoleacetic acid (IAA), are critical plant hormones regulating growth and development.
- Understanding auxin's effect on plasma membrane permeability is key to elucidating its physiological roles.
Purpose of the Study:
- To investigate the physiological effects of auxin on isolated oat coleoptile protoplasts.
- To determine the role of potassium ions (K+) and glucose in auxin-mediated protoplast swelling.
Main Methods:
- Isolation of iso-osmotic protoplasts from oat (Avena sativa L.) coleoptile segments.
- Measurement of protoplast swelling over time under various ionic and osmotic conditions.
- Application of indoleacetic acid (IAA) and assessment of its impact on swelling dynamics.
- Testing the effects of K+, glucose (Glc), sodium azide (NaN3), and sodium orthovanadate.
Main Results:
- Protoplasts exhibited steady swelling over several hours in a standard bathing medium.
- Indoleacetic acid (IAA) significantly enhanced protoplast swelling.
- Auxin-induced swelling was strictly dependent on external K+, while basal swelling showed partial K+ dependence.
- Glucose replaced mannitol increased basal swelling but abolished IAA-induced swelling.
- Swelling was inhibited by osmotic shock and reversed by sodium azide; vanadate showed gradual inhibition.
Conclusions:
- Indoleacetic acid (IAA) increases the plasma membrane's conductance to potassium ions (K+).
- The observed auxin-induced swelling is a K+-dependent process modulated by external glucose levels.
- These findings suggest a novel mechanism for auxin action at the plasma membrane level.
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