Herbicide effects on phenolic metabolism in maize (Zea mays L.) and soybean (Glycine max L.) seedlings

The activities of phenylalanine ammonia lyase [PAL; EC 4.3.1.5] and chalcone isomerase [CI; EC 5.5.1.5] as well as the contents of anthocyanin and total soluble hydroxyphenolic compounds were investigated in maize (Zea mays L.) and soybean (Glycine max L.) seedlings 120 h after treatment with the field dose of five herbicides from different groups (trifluralin, fluometuron, atrazine, alachlor, and rimsulfuron) having varied modes of action. The fresh weight of both species was greatly decreased by trifluralin followed by fluometuron and atrazine. The dry weight was, in general, only slightly decreased by all the herbicides with the largest response with trifluralin. On the other hand, the activities of PAL and CI were greatly enhanced in both species by alachlor and rimsulfuron, but decreased by trifluralin. Fluometuron induced decreases in PAL activity of maize only and decreased CI activity of maize and soybean seedlings. Moreover, hydroxyphenolic compounds were increased in both species by alachlor and rimsulfuron and decreased by trifluralin and atrazine. Similarly, anthocyanin content was increased in both seedlings by alachlor and rimsulfuron, but decreased by trifluralin and fluometuron, whereas atrazine decreased the anthocyanin content in maize only. The present results indicate that stress is maintained by the different herbicides and confirm the controlling action of PAL and CI on the production of anthocyanin and phenolic compounds during the induced state of stress. In addition, dry weight reduction appeared to coincide with the changes in the parameters of secondary metabolism, suggesting a regulatory role of secondary metabolism on seedling growth.