The Role of Cl- in Pollen Germination and Tube Growth

The involvement of Cl- in cytoplasm polarization in the pollen tube and membrane potential control during pollen germination in vitro was studied by fluorescence techniques in Nicotiana tabacum. Cl- release from cells was blocked by the anion channel inhibitor nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) or by the addition of Cl- to the incubation medium. The concentrations of the inhibitor (40 mu M) and extracellular Cl- completely inhibiting pollen germination (200 mM) and pollen tube growth (100 mM) were used. The release of anions from the pollen grain has been revealed in the first minutes of hydration also in the presence of 200 mM Cl-. The inhibitor blocked this process completely, which points to the significance of the NPPB-sensitive anion channels in the transmembrane Cl- transport at the early activation stage. The pollen tube membrane was hyperpolarized in the presence of 100 mM Cl-; however, exogenous Cl- had no effect on the compartmentalization and organelle movement in the tube. The inhibitor depolarized the plasma membrane in the pollen grain and tube and affected the polar organization of the cytoplasm and organelle movement. Thus, activity of NPPB-sensitive chloride channels was required to regulate the potential on the plasma membrane and to maintain the functional compartmentalization of the cytoplasm, which provides for the polar growth.