Gramicidin-D-stimulated influx of monovalent cations into plant roots.

Gramicidin D and nigericin were found to stimulate K(+) influx into oat roots. Valinomycin and nonactin had little effect on K(+) influx. The region of the root most sensitive to gramicidin was the elongation zone. Monocot roots were more sensitive to gramicidin than dicot roots. At 0.2 mM KCl, gramicidin stimulated K(+) influx by 4- to 8fold over a 30-min absorption period. Although a gramicidin response is detectable within one minute, maximum stimulation occurred after a slight (approximately 2-min) lag period. The gramicidin effect was much greater at 0.2 mM KCl than at 20 mM KCl. Respiratory inhibitors reduced the gramicidin-stimulated K(+) influx by 50-80%. The results are discussed in terms of possible mechanisms of action of the various ionophores on ion transport in roots.