The micronutrient deficiency during the critical growth period of Lettuce (Lactuca sativa L.) by its controlling the plant intake of micronutrients can have a profound impact on yield, especially under hydroponic conditions and controlled environmental systems such as greenhouse. Boron (B) and Zinc (Zn) play a key role in plants as these are essential micronutrients of nutritional solutions for securing the crop quality and yield. The work was designed as a factorial experiment on based randomized complete block design with three replications for two factors of zinc (ZnSO4 ,7H2O) at three levels (0, 5, and 10mg/l) and boron (H3BO3 ) at three levels (0, 2 and 4mg/l) on quantitative and qualitative traits of lettuce under hydroponic conditions. The results demonstrated that as the concentration of zinc increased in the nutrient solution, the fresh and dry weight, chlorophyll index, chlorophyll a and b, total chlorophyll, carotenoids content, total protein concentration, and leaf zinc concentration significantly increased. Increasing in boron concentration significantly increased the proline content, malondialdehyde (MDA) content, guaiacol peroxidase (GPX), catalase (CAT), and ascorbate peroxidase (APX) activity levels and also leaf boron concentration. Adding zinc to the solution mitigated the adverse effects of high concentrations of boron on the mentioned parameters. According to the antagonistic relation between Zn and B, under high levels of B in nutrient solutions, supplementing the lettuce with adequate Zn is recommended.
