Irrigation with industrial wastewater activates antioxidant system and osmoprotectant accumulation in lettuce, turnip and tomato plants

Abstract

We focused on the impact of industrial wastes on the water quality of the El-Amia drain in Egypt and the effect of irrigation with industrial wastewater on the growth, cell membranes, photosynthetic pigment content, the antioxidant system and selected osmoprotectants (proline, total amino nitrogen and soluble sugars) in three crop plants: turnip, tomato and lettuce. Furthermore, the present work focused on the analysis of the heavy metal content and its accumulation in the studied plants. For this purpose, water samples were collected 1, 10 and 19km from the beginning of the drain and used for irrigation, with fresh water as a control. We found that industrial wastewater contained significant amounts of heavy metals (Cd, Ni and Co) warranted a pollution problem as their amounts exceed the maximum recommended concentrations according to FAO guidelines for trace metals in irrigation water. The three crop plants accumulate significant amounts of heavy metals in their shoots and roots and showed a significant decrease in leaf area, fresh weight and dry weight of shoots and roots, accompanied by a marked reduction in photosynthetic pigment content and damage to cell membranes, as indicated by increased electrolyte leakage and a lower membrane stability index. Significant increases in the activities of antioxidant enzymes and in the glutathione, proline, soluble sugar and total amino nitrogen content in response to irrigation with wastewater may be defense mechanisms induced in response to heavy metal stress.