Computer-assisted Video Image Analysis of Spatial Variations in Membrane-associated Ca2+ and Calmodulin during Pollen Hydration, Germination and Tip Growth in Nicotiana tabacum L.

Abstract

Video images of the distributional pattern of membrane-associated calcium (Ca2+) and calmodulin (CaM) have been documented and analysed during pollen hydration, germination and tip growth in Nicotiana tabacum. Digitization of fluorescence microscope images of chlorotetracycline (CTC) and fluphenazine (FPZ)-fluorescence emissions reveal that there is a maximum concentration of membrane-associated Ca2+ and also CaM in the vicinity of germination apertures of hydrated pollen. With the onset of germination relatively higher amounts of Ca2+ and CaM were found to regionalize towards the aperture through which the pollen tube would emerge. Both short and long growing pollen tubes manifest tip-to-base Ca2+ and CaM gradients which are disturbed in non-growing tubes. Tube growth and the Ca2+-gradient were significantly affected by vanadate and verapamil suggesting that both a vanadate-sensitive Ca2+-transport system and verapamil-sensitive Ca2+ channels are involved in maintaining Ca2+ homeostasis during pollen germination and tube growth. The possible interactions of Ca2+ and CaM with different cytoskeletal proteins modulating organelle movement are also briefly discussed.