DISTRIBUTION OF CALMODULIN PROTEIN AND MESSENGER-RNA IN GROWING POLLEN TUBES

Pollen tube growth is a vital process for angiosperm fertilisation and is dependent on the presence of a tip-focused gradient of cytosolic f ree calcium ([Ca2+](c)). In order to clarify some of the target molecu les which convey the Ca2+ signal information, we investigated calmodul in distribution during tube growth. Fluorescently labelled calmodulin was pressure microinjected into pollen tubes and its distribution moni tored by confocal microscopy. Calmodulin distributes evenly throughout the cell, but some of its binding sites form a V-shaped collar behind the apical region. This specific association dissipates upon growth a rrest, and suggests an interaction of calmodulin with cytoskeletal-bou nd target proteins. The distribution of calmodulin mRNA was also analy sed by microinjection of fluorescently labelled mRNA. No specific patt ern was observed, with an even localisation in the body of tube and a lower concentration in the cell apex. Studies with localised applicati on of inhibitors/activators indicate that calmodulin plays a crucial r ole in tip elongation but does not direct tube orientation.