Pump up the volume - a central role for the plasma membrane H+ pump in pollen germination and tube growth

The plasma membrane H+ ATPase is a member of the P-ATPase family transporting H+ from the cytosol to the extracellular space and thus energizing the plasma membrane for the uptake of ions and nutrients. As a housekeeping gene, this protein can be detected in almost every plant cell including the exclusive expression of specific isoforms in pollen grains and tubes where its activity is a prerequisite for successful germination and growth of pollen tubes. This review summarizes the current knowledge on pollen PM H+ ATPases and hypothesizes a central role for pollen-specific isoforms of this protein in tube growth. External as well as cytosolic signals from signal transduction and metabolic pathways are integrated by the PM H+ ATPase and directly translated to tube growth rates, allocating the PM H+ ATPase to an essential node in the signalling network of pollen tubes in their race to the ovule.