Ion transport in the pitcher of Nepenthes henryana

Abstract

Ion transport in the pitcher of Nepenthes henryana has been studied:

• 1.

  1. Apparent concentrations of Na⁺, K⁺, H⁺, Ca²⁺, Mg²⁺ and Cl⁻ in the pitcher tissue and liquid were determined.

• 2.

  2. By 24-h dialysis of the pitcher liquid against redistilled H₂O about 90% of the K⁺ and Cl⁻ were removed, as compared with only 10% Na⁺.

• 3.

  3. The apparent membrane potentials for Na⁺, K⁺ and Cl^- at the interphase pitcher tissue-liquid were calculated according to the Nernst equation.

• 4.

  4. Using microelectrodes, the membrane potential of the cells lining the inner surface of the pitcher was found to be $\text{35 ± 3.7}\text{mV}$ (range 17–55 mV; 48 measurements in a total of 10 plants). The tissue was negative with respect to the pitcher liquid.

• 5.

  5. In Na⁺-containing media a potential difference of 30–50 mV and a short-circuit current of 10–20 μA/cm² across the pitcher wall were found. Both of these values were decreased by 0.4 mM 2,4-dinitrophenol or 0.4 mM HgCl₂.

• 6.

  6. Na⁺ in the bathing liquid produced a short-circuit current in the direction: $\text{inner compartment → pitcher tissue → outer medium}$; K⁺ and Cl⁻ brought about currents in the opposite direction.

• 7.

  7. The mechanism of the transport of Na⁺, K⁺ and Cl⁺ in the pitcher is discussed.