Ma. Messerli et al., Pulsatile influxes of H+, K+ and Ca2+ tag growth pulses of Lilium longiflorum pollen tubes, J CELL SCI, 112(10), 1999, pp. 1497-1509
Fluxes of H+, K+ and Ca2+ were measured with self-referencing ion-selective
probes, near the plasma membrane of growing Lilium longiflorum pollen tube
s. Measurements from three regions around short, steady-growing tubes showe
d small, steady influx of H+ over the distal 40 mu m and a region of the tu
be within 50-100 mu m of the grain with larger magnitude efflux from the gr
ain. K+ fluxes were immeasurable in short tubes. Measurements of longer tub
es that were growing in a pulsatile manner revealed a pulsatile influx of b
oth H+ and K+ fat the growing tip. The average fluxes at the cell surface d
uring the peaks of the H+ and K+ pulses were 489 +/- 81 and 688 +/- 144 pmo
l cm(-2) second(-1), respectively. Growth was measured by tracking the poll
en tips with a computer vision system that achieved a spatial resolution of
approximately 1/10 pixel. The high spatial resolution enabled the detectio
n 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 p
hase 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, t
he calcium influx was relatively steady. When pulsatile growth began, the b
asal Ca2+ influx decreased and a pulsatile component appeared, superimposed
on the reduced basal Ca2+ flux. The peaks of the Ca2+ pulses at the cell s
urface 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.