Attenuating the toxicity of isoproturon to maize by priming in ascorbate, glutathione or thiourea

Maize grains were primed in ascorbate (AsA), glutathione (GSH) or thiourea (TU) for 24 h, sown in pots for 10 days and then treated with Ipu whose residues persisted in shoots from the next day and increased over 8 days and then decreased continuously. The herbicide significantly reduced growth parameters, pigments, photosynthetic activity parameters, AsA, GSH and GSH/oxidized glutathione (GSSG) ratio and inhibited the activities of δ-aminolevulinate dehydratase (ALA-D), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEP-C), malate dehydrogenase (MDH), pyruvate phosphate dikinase (PPDK), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) but significantly increased malondialdehyde (MDA), H2O2, superoxide radicals (O2∙−) and GSSG. The priming mostly improved the tested parameters and overcame the deficiency in enzymatic and non-enzymatic antioxidants as well as in the photosynthetic parameters and enzyme activities; AsA or GSH were more efficient than TU. Besides, in vitro tests showed that the inhibition constant (IC50) for Ipu was lowest for CAT but highest for PPDK indicating that CAT was the most inhibited but PPDK was the least while the others were moderate. Furthermore, calculations showed that Ipu competitively inhibited ALA-D, Rubisco, APX, PEP-C, MDH and PPDK but caused non-competitive inhibition of APX, CAT and SOD. These findings reveal that maize was prone to suffering from Ipu; however, priming attenuated the toxicity of Ipu and overcame the herbicide impacts by repairing, maintaining and improving antioxidants and photosynthetic activities.