Glutathione S-transferases of italian ryegrass (Lolium multiflorum): activity toward some chemicals, safener modulation and persistence of atrazine and fluorodifen in the shoots

Many varieties of Italian ryegrass (Lolium multiflorum) show resistance to herbicides; while this ability was frequently attributed to alterations in the target sites of the herbicide's action of the plant or to an efficient oxidative metabolism, little attention has been paid to glutathione S-transferases (GSTs), which are a family of detoxifying enzymes involved in the inactivation of many toxic compounds. To investigate the role of GSTs, seedlings of Italian ryegrass were treated with four herbicides (atrazine, fenoxaprop-ethyl, fluorodifen, metolachlor) and a safener (fenchlorazol-ethyl). All the treatments were well tolerated by the plant, with very low decreases in terms of fresh weight and length of shoots. Regarding GST activity, the chemicals generally determined significant increases in the above enzyme activity toward the model-substrate CDNB. Therefore, the herbicides most GST inducing and the safener were tested themselves as enzyme substrates: constitutive GST activities toward atrazine, fluorodifen and fenchlorazol-ethyl were found, and, in addition, these activities were significantly induced by the safener. Following these results, a HPLC procedure was standardized in order to investigate the persistence of atrazine and fluorodifen in the seedlings of Italian ryegrass and the effect on this of the safener. It was found that the residual amounts of the two herbicides in the shoots were significantly reduced following the safener treatments.