Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Ion Fluxes and Phytochrome Protons in Mung Bean Hypocotyl Segments: I. Fluxes of Potassium

Colin Brownlee and Richard E. Kendrick
Plant Physiology
Vol. 64, No. 2 (Aug., 1979), pp. 206-210
Stable URL: http://www.jstor.org/stable/4265871
Page Count: 5
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Preview not available

Abstract

$\text{K}^{+}[^{86}\text{Rb}^{+}]$ uptake by Phaseolus aureus Roxb. hypocotyl segments cut immediately below the hook is inhibited by the active form of phytochrome (Pfr). Short load-short wash experiments indicate that the inhibition of uptake occurs across the plasmalemma. A maximal inhibition of short term uptake occurs in 10 to 50 millimolar KCl. Low temperature had only a small effect on influx and the inhibition of influx from 50 millimolar KCl. A consideration of the electrochemical gradient for K+ suggests that passive K+ fluxes may predominate under these conditions. Red light induces small depolarizations of membrane potential in subhook cells. Far red light antagonizes this effect. Pfr inhibits efflux of $\text{K}^{+}[^{86}\text{Rb}^{+}]$ from subhook segments. This effect is also relatively insensitive to low temperature. This inhibition of efflux may reflect inhibition of a K+-K+ exchange process, or reduced passive permeability of the plasmalemma to K+. In contrast, Pfr enhances short term uptake of $\text{K}^{+}[^{86}\text{Rb}^{+}]$ in apical hypocotyl hook segments of Phaseolus aureus Roxb. Short load-short wash experiments indicate that fluxes across the plasmalemma are modified by Pfr. A maximal enhancement of short term influx occurs in 50 millimolar KCl. Influx and the red light enhancement of influx from 50 millimolar KCl are relatively insensitive to low temperature. Pfr also enhances efflux of $\text{K}^{+}[^{86}\text{Rb}^{+}]$ from preloaded apical hook segments. This increased influx may reflect enhancement of a K+-K+ exchange process or increased passive permeability of the plasmalemma to K+.

• 206
• 207
• 208
• 209
• 210