ATP-dependent glutathione S-conjugate 'export' pump in the vacuolar membrane of plants

PLANTS are exposed to many potentially phytotoxic foreign compounds, such as microbial toxins and agrochemicals (xenobiotics). Detoxification and elimination of these compounds within or from the cell is a prerequisite for their survival. Metabolism and detoxification of xenobiotics are remarkably similar in plants and animals and can generally be divided into three phases^1,2. In the first phase, a foreign compound may be oxidized, reduced or hydrolysed to introduce or reveal a functional group. In a second step, the activated xenobiotic is conjugated to either glutathione, glucuronate (animals), or malonyl or glucosyl moieties (plants) by the respective transferases. In animals the third step, excretion of conjugated xenobiotics to the extracellular medium, is mediated by a specific ATPase^1,3-5. In plants, instead of excretion, conjugates of xenobiotics appear to be stored in the large central vacuole⁶, but it is not known how they are transported into this organelle. We show here that glutathione S-conjugate uptake into the vacuole is mediated by a specific ATPase which is remarkably similar to the glutathione S-conjugate export pumps in the canalicular membrane of mammalian liver.