ATP-DEPENDENT GLUTATHIONE S-CONJUGATE EXPORT PUMP IN THE VACUOLAR MEMBRANE OF PLANTS

PLANTS are exposed to many potentially phytotoxic foreign compounds, s uch as microbial toxins and agrochemicals (xenobiotics). Detoxificatio n and elimination of these compounds within or from the cell is a prer equisite for their survival. Metabolism and detoxification of xenobiot ics are remarkably similar in plants and animals and can generally be divided into three phases1,2. In the first phase, a foreign compound m ay be oxidized, reduced or hydrolysed to introduce or reveal a functio nal group. In a second step, the activated xenobiotic is conjugated to either glutathione, glucuronate (animals), or malonyl or glucosyl moi eties (plants) by the respective transferases. In animals the third st ep, excretion of conjugated xenobiotics to the extracellular medium, i s mediated by a specific ATPase1,3-5. In plants, instead of excretion, conjugates of xenobiotics appear to be stored in the large central va cuole6, but it is not known how they are transported into this organel le. We show here that glutathione S-conjugate uptake into the vacuole is mediated by a specific ATPase which is remarkably similar to the gl utathione S-conjugate export pumps in the canalicular membrane of mamm alian liver.