Redox-regulation of ion homeostasis in growing lily pollen tubes.

The pollen tube is characterized by cytoplasm compartmentalization typical for cells with polar growth. This concept includes "ion zoning", i.e. gradient distribution of ionic currents across the plasma membrane and free inorganic ions in the cytoplasm. One of the putative mechanisms for maintaining "ion zoning" is indicated by the sensitivity of the ion transport systems to reactive oxygen species (ROS). Here we test the possibility of redox regulation of ionic gradients and membrane potential (MP) gradient in growing pollen tubes using quantitative fluorescence microscopy. ROS quencher MnTMPP and exogenic H2O2 cause different alterations of intracellular Ca2+ gradient, pH gradient and MP gradient during short-term exposure. MnTMPP significantly shifts the gradients of Ca2+ and MP at low concentrations while high concentration cause growth alterations (ballooned tips) and cytoplasm acidification. H2O2 at 0,5 and 1 mM affects ion homeostasis as well (MP, Ca2+, pH) but doesn't decrease viability or alter shape of the tubes. Here we present original quantitative data on the interconnection between ROS and ion transport during tip growth.