Pulsatile influxes of H⁺, K⁺ and Ca²⁺ lag growth pulses of Lilium longiflorum pollen tubes

Fluxes of H⁺, K⁺ and Ca²⁺ were measured with self-referencing ion-selective probes, near the plasma membrane of growing Lilium longiflorum pollen tubes. Measurements from three regions around short, steady-growing tubes showed small, steady influx of H⁺ over the distal 40 μm and a region of the tube within 50-100 μm of the grain with larger magnitude efflux from the grain. K⁺ fluxes were immeasurable in short tubes. Measurements of longer tubes that were growing in a pulsatile manner revealed a pulsatile influx of both H⁺ and K⁺ at the growing tip. The average fluxes at the cell surface during the peaks of the H⁺ and K⁺ pulses were 489 ± 81 and 688 ± 144 pmol cm^-2 second^-1, respectively. Growth was measured by tracking the pollen tips with a computer vision system that achieved a spatial resolution of approximately 1/10 pixel. The high spatial resolution enabled the detection of growth, and thus the changes in growth rates, with a temporal sampling rate of 1 frame/second. These data show that the H⁺ and K⁺ pulses have a phase lag of 103 ± 9 and 100 ± 11 degrees, respectively, with respect to the growth pulses. Calcium fluxes were also measured in growing tubes. During steady growth, the calcium influx was relatively steady. When pulsatile growth began, the basal Ca²⁺ influx decreased and a pulsatile component appeared, superimposed on the reduced basal Ca²⁺ flux. The peaks of the Ca²⁺ pulses at the cell surface averaged 38.4 ± 2.5 pmol cm^-2 second^-1. Longer tubes had large pulsatile Ca²⁺ fluxes with smaller baseline fluxes. The Ca²⁺ influx pulses had a phase lag of 123 ± 9 degrees with respect to the growth pulses.