gramicidin-a and 4-phenylenediamine

The photoinduced currents in whole chloroplasts of Peperomia metallica were studied using suction electrodes and single-turnover flashes. The kinetic profile of the photocurrent contained a minor outward component (rise time, 100 micros). Local application (from the inside of the pipette) of a photosystem 2 inhibitor, DCMU, rapidly suppressed the outward current; conversely, addition of DCMU to the outer medium produced a transient stimulation of the outward component. Permeabilization of the tip-located membrane fragments with Triton X-100 eliminated the outward current, but had no significant influence on the inward current. The data suggest that the outward current originated in the tip-located nonruptured portions of the thylakoid membrane. Different involvement of two photosystems in the generation of the outward current indicates that granal thylakoids enriched with photosystem 2 are less susceptible to the rupture in the pipette tip as compared with stromal thylakoids.

Topics: Anti-Bacterial Agents; Chloroplasts; Coloring Agents; Detergents; Diuron; Energy Transfer; Gramicidin; Herbicides; Light; Membrane Potentials; Methylphenazonium Methosulfate; Octoxynol; Patch-Clamp Techniques; Phenylenediamines; Photosynthetic Reaction Center Complex Proteins; Piperaceae; Plant Leaves