Hyperpolarisation-activated calcium currents found only in cells from the elongation zone of Arabidopsis thaliana roots

Calcium currents across the plasma membrane of plant cells allow transducti on of environmental signals as well as nutritive calcium uptake. Using tran sgenic Arabidopsis plants with cell-specific expression of green fluorescen t protein (GFP), we analyzed whole cell calcium currents in epidermal cells of the rapidly growing root apex, mature epidermal cells, cortical and epi dermal cells from the elongation zone, and mature pericycle cells. In cells only from the rapidly growing root apex, a hyperpolarisation-activated cal cium current was identified. This current was irreversibly inhibited by 10 mu m Al3+, as well as being inhibited by 1 mm Co2+ and 100 mu m verapamil. In no cells could a depolarisation-activated current be attributed to calci um influx. In the growing root apex, the hyperpolarisation-activated calciu m current may function to allow constitutive uptake of calcium for rapid ce ll division and elongation.