Pollen Tube Growth and the Intracellular Cytosolic Calcium Gradient Oscillate in Phase while Extracellular Calcium Influx Is Delayed.
Ratio images of cytosolic Ca2+ (Ca2+i) in growing, fura-2-dextran-loaded Lilium longiflorum pollen tubes taken at 3- to 5-sec intervals showed that the tip-focused [Ca2+]i gradient oscillates with the same period as growth. Similarly, measurement of the extracellular inward current, using a noninvasive ion-selective vibrating probe, indicated that the tip-directed extracellular Ca2+ (Ca2+o) current also oscillates with the same period as growth. Cross-correlation analysis revealed that whereas the [Ca2+]i gradient oscillates in phase with growth, the influx of Ca2+o lags by ~11 sec. Ion influx thus appears to follow growth, with the effect that the rate of growth at a given point determines the magnitude of the ion influx ~11 sec later. To explain the phase delay in the extracellular inward current, there must be a storage of Ca2+ for which we consider two possibilities: either the inward current represents the refilling of intracellular stores (capacitative calcium entry), or it represents the binding of the ion within the cell wall domain.
Holdaway-Clarke
T. L.
TL
Biology Department, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts 01003.
Feijo
J. A.
JA
Hackett
G. R.
GR
Kunkel
J. G.
JG
Hepler
P. K.
PK