May constitute a glutathione peroxidase-like protective system against oxidative stresses. Involved positively in abscisic acid (ABA) signaling pathway that regulates numerous ABA responses, such as stomatal closure, seed germination and inhibition of vegetative growth. Oxidizes and represses target proteins (e.g. the phosphatase activity of ABI1 and ABI2) when oxidized by H(2)O(2), probably after ABA signaling. Modulates the calcium channel activity in guard cells in response to ABA or H(2)O(2). Confers tolerance to drought stress, by enhancing the ABA-dependent stomatal closure. 2 glutathione + H2O2 = glutathione disulfide + 2 H2O The redox states are modulated by H(2)O(2). Interacts with ABI1 and ABI2. Ubiquitous. By osmotic stress, H(2)O(2), drought stress, and metals. Regulated by abscisic acid (ABA); down-regulated by 1 mM ABA (PubMed:14617062), whereas induced by 60 uM ABA (PubMed:16998070). Leaves of plants lacking GPX3 are 1 degree Celsius lower than normal plants, whereas leaves from plants over-expressing GPX3 are 1.2 degrees Celsius higher, probably because of the impaired evapotranspiration. The reduced form of ABI2 is converted to the oxidized form by the addition of oxidized GPX3. Belongs to the glutathione peroxidase family.