Effects of terbuthylazine on iron-deficient barley: interferences on phytosiderophores release and on sulfur metabolism

Herbicides are very diffused agrochemicals in agriculture for weed control; some of them, due to their persistence, can damage non-target plants and interfere with their ability to acquire some nutrients. This work was aimed to assess the effect of terbuthylazine (TBA), which is a triazine herbicide widely used for weeding and highly persistent in the environment, on Fe-deficient barley plants. Results showed that TBA generally reduces chlorophyll content, length and fresh weight of the plants, although such disturbances have been observed at a sub-lethal level. In plants treated with TBA, the release of phytosiderophores (PS) has been significantly reduced starting from the first hours after the treatment, and this effect was associated with the decrease of the levels of transcripts of genes involved in the synthesis and transport of PS. Due to the importance of these molecules in iron (Fe) mobilization and acquisition and their dependency on sulfur (S) metabolism, the activity of ATPS and of OASTL, two key-enzymes in sulphate assimilation, was analyzed, and the contents of cysteine and glutathione were determined. The TBA treatments strongly reduced the ability of plants to assimilate sulphate. A confirmation was found in the decrease of cysteine and glutathione content observed in treated plants. The results of this study clearly highlight that an herbicide can strongly and negatively interfere with the sulfur assimilation and release of phytosiderophores of barley, a very important crop at global level.