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  • Title: Pollen Tube Growth and the Intracellular Cytosolic Calcium Gradient Oscillate in Phase while Extracellular Calcium Influx Is Delayed.
    Author: Holdaway-Clarke TL, Feijo JA, Hackett GR, Kunkel JG, Hepler PK.
    Journal: Plant Cell; 1997 Nov; 9(11):1999-2010. PubMed ID: 12237353.
    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.
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