THE ACCUMULATION OF ELECTROLYTES : VI. THE EFFECT OF EXTERNAL pH

Area of Science:

• Plant Physiology
• Cell Biology
• Biochemistry

Background:

• Potassium (K+) is a vital ion for plant cells.
• The transport mechanism of potassium into Valonia cells was previously unclear.
• Potassium in Valonia sap is observed as potassium chloride (KCl).

Purpose of the Study:

• To investigate the primary form of potassium entry into Valonia cells.
• To determine the mechanism governing potassium transport across the cell membrane.
• To test the hypothesis that potassium enters as KOH based on ionic activity products.

Main Methods:

• Experimental observation of potassium and sodium transport.
• Manipulation of external pH to assess its effect on potassium influx.
• Analysis of ionic activity products (K+)(OH-) inside and outside the cell.

Main Results:

• Potassium transport is best predicted by assuming entry as potassium hydroxide (KOH).
• Potassium efflux occurs when the (K+)(OH-) product is higher inside the cell.
• Increased external pH enhances potassium influx, suggesting a role in photosynthesis.

Conclusions:

• Potassium enters Valonia cells mainly as KOH, regulated by the (K+)(OH-) ionic activity product.
• The hypothesis of KOH entry explains observed potassium transport behaviors, including efflux and pH-dependent influx.
• Photosynthesis appears to facilitate potassium uptake by increasing external pH near the protoplasm.