title: Pollen Tube Growth and the Intracellular Cytosolic Calcium Gradient Oscillate in Phase while Extracellular Calcium Influx Is Delayed.
abstract: 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.
authors.affiliation: Biology Department, Morrill Science Center, University of Massachusetts, Amherst, Massachusetts 01003.
authors.forename: T. L.
authors.initials: TL
authors.lastname: Holdaway-Clarke
authors.forename: J. A.
authors.initials: JA
authors.lastname: Feijo
authors.forename: G. R.
authors.initials: GR
authors.lastname: Hackett
authors.forename: J. G.
authors.initials: JG
authors.lastname: Kunkel
authors.forename: P. K.
authors.initials: PK
authors.lastname: Hepler