Ion dynamics during oscillating growth of Lilium longiflorum pollen tubes
Abstract
Ca2+, K+ and an acidic pH are required for the growth of lily pollen tubes in vitro. We have studied the spatial and temporal changes of these ions in and around pollen tubes during tip growth in order to understand their roles during tip growth. Specifically we have studied the relationship of the transport of these ions to growth oscillations when pollen tube growth rates oscillate between 0.1 and 0.4 μm/s with periods of 40 s. It is well known that pollen tubes grown in vitro both contain and require a tip-high gradient of Ca2+ in order to elongate. We show that during growth oscillations the [Ca2+] i oscillates between 3 and 10 μM during growth oscillations. The changes in the tip [Ca2+] lag the changes in growth rate with a phase shift of 38°. We also show, however, that an extracellular influx of Ca2+ lags the changes in growth rate with a larger phase shift of 123°. While the presence of a steady, intracellular gradient of H+ during tip growth remains controversial, we measured oscillatory increases of the tip [H+]. The tip pH decreased by between 0.1 and 1 pH unit during the peaks of the H+ oscillations from a basal pH of 7. We also measured an extracellular influx of H+ that occurred at nearly the same time as the increases in intracellular H + and lagged the growth oscillations by 103°. In conjunction with the measurements of oscillating H+ influx we measured an oscillating influx of K+. The magnitude of the peaks of K+ influx was not statistically different from the magnitude of the peaks of the H+ influx and occurred at nearly the same time as the H + influx, lagging growth oscillations by 100°. With these new data we propose that the surges of Ca2+ which occur after the surges in growth are promoting vesicle fusion such that each growth surge is dependent on materials added during the previous rise in the [Ca2+]i and that the oscillations in K + influx are directly linked to changes in turgor pressure and are driven by cotransport with H+.
Degree
Ph.D.
Advisors
Robinson, Purdue University.
Subject Area
Plant sciences
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.