Cytoplasmic acidification and current influx follow growth pulses of Lilium longiflorum pollen tubes

We confirm that there is not a standing pH gradient in the tips of lily pollen tubes, but show that there are pulses of H+ that occur during pulsatile growth. The [H+] increases in a zone at the tips of the tubes and travels rapidly as far as 60 mu m down the shaft of the tube. The tip-localized pH was found to drop to 6.0 during the largest pulses, from an average cytosolic level of 7.05 in tubes that had not yet begun to pulse. Correlation analysis indicates that the peaks of the pH pulses lag the peaks of the growth pulses by slightly more than 7.5 sec. Vibrating probe measurements reveal an influx of ionic current that peaks 7.5 sec after the peaks of the growth pulses. While this current may in part be H+ influx, we give evidence that K+ influx is also a component of the current pulses. The timing of the H+ and current pulses suggests that they may be involved in terminating the growth pulses.