[Membrane potential changes during pollen germination and tube growth]

We applied quantitative fluorescent microscopy to study membrane potential alterations during pollen germination and in growing pollen tube. Two voltage-sensitive dyes were applied: DiBAC4(3) was used to detect average membrane potential values in pollen grains and isolated protoplasts; Di-4-ANEPPS gave an option of membrane potential mapping on pollen protoplast and pollen tube surfaces. We have found out that tobacco pollen grain activation is accompanied by hyperpolarization of the vegetative cell plasma membrane by about 8 mV. Lily pollen protoplasts were significantly hyperpolarized (-108 mV) with respect to the pollen grains (-23 mV) from which they were isolated. We found polar distribution of the membrane potential along the protoplast surface, and longitudinal potential gradient along the pollen tube. In the presence of plasma membrane H(+)-ATPase inhibitor, sodium orthovanadate (1 mM) or its activator fusicoccin (1 microM), the longitudinal voltage gradient altered but did not disappear. Anion channel blocker, NPPB (40 microM), fully discarded the gradient in pollen tubes. Obtained results give evidence of the plasma membrane hyperpolarization during pollen germination and uneven potential distribution on pollen grain and tube surfaces. Inhibitory analysis showed involvement of the plasma membrane H(+)-ATPase and anion channels in membrane potential regulation.