Physiological and biochemical responses of soybean (Glycine max L.) to cysteine application under sea salt stress

Background Shortage of water is a major problem facing Egypt; thus, it becomes necessary to use non-traditional sources of water such as saline water in irrigation. Overcoming the adverse effects of saline water and enhancing plant tolerance to salinity stress is the main challenge for increasing plant growth and productivity. Using a natural compound such as cysteine amino acid has an important effect in alleviating the adverse effect of salinity stress on different plant crops. Materials and methods Two pot experiments were carried out during two successive summer seasons to study the beneficial role of cysteine (0, 20, and 40 mg/l) in enhancing growth, some metabolic process, and seed yield quality and quantity of soybean plant grown under salinity stress (0, 3000, and 6000 mg/l). Results Salinity stress (3000 and 6000 mg/l) caused decreases in soybean growth criteria (plant height, number of branches and leaves/plant, dry weight of leaves and stem/plant), photosynthetic pigments and some element contents (nitrogen (N), phosphorus (P), and potassium (K)), and seed yield and yield components (number of pods/plant, weight of pods/plant and number of seeds/plant) as well as oil%. Meanwhile, proline, H 2 O 2 and MDA contents, and superoxide dismutase activity were gradually increased by increasing salinity level. On the other hand, cysteine treatments improved growth and yield of soybean plant either irrigated with tap water or saline water. Cysteine treatments could alleviate the adverse effect of salinity stress on growth and yield of soybean plant through increasing photosynthetic pigments; proline content; N, P, and K contents; superoxide dismutase and catalase activities; and oil% accompanied by decreases in H 2 O 2 and MDA contents as compared with their corresponding controls. In addition, cysteine treatments and/or salinity stress exhibited differences in protein pattern from 112 to 19 kD molecular weight. The appearance of new protein bands reflected the expression of cysteine treatments and salinity stress. Conclusion Cysteine treatments had a beneficial role in alleviating the adverse effect of salinity stress on soybean plant. Forty milligrams per liter of cysteine was the most effective treatment in enhancing salinity tolerance of soybean plant.