Intervening Role of Tyrosine in Cadmium Detoxification, Balancing of Mineral Ions Homeostasis, Antioxidants, and Secondary Metabolites in Maize

Cadmium (Cd) is a hazardous and non-essential heavy metal which cannot be degraded either biologically or chemically, thus posing a permanent threat to growth and yield of plants. We have investigated the contribution of exogenously applied tyrosine on growth, nutrient ion acquisition, antioxidants, and osmolyte activities under different Cd concentrations. Four levels of Cd (0, 0.2, 0.4, 0.6 mM) and three levels of tyrosine (0, 50, 100 mg L−1) were applied on maize plants grown in soil filled plastic pots. The applied Cd stress levels, especially 0.6 mM of Cd, significantly decreased the shoot fresh weight (64.70%), root fresh weight (69.11%), shoot dry weight (78.46%), root dry weight (67.03%), root and shoot calcium (47.61%, 44.8%), manganese (65.8%, 72.56%), nitrogen (55.68%, 43.99%), ferris (51.9%, 60.86%), zinc (66.57%, 72.05%), and potassium (56.82%, 55%). Conversely, foliar spray application of tyrosine proved to be more effective in removing the negative effects of Cd in studied traits. Under 0.6 mM Cd stress, foliar spray of tyrosine (100 mg/kg) increased the shoot fresh weight (10.2%), root fresh weight (29.76%), root dry weight (30.22%), shoot dry weight (20.2%), root and shoot calcium, (44.73%, 28.98%), manganese (41.36, 43.46%), nitrogen (20.84%, 50.6%), ferris (29.64%, 50.66%), zinc (58.1%, 50.6%), and enzyme activities such as superoxide dismutase (14.16%), peroxidase (13.55%), catalase (17.98%), and ascorbate peroxidase (20.68%), while lowered down the malondialdehyde (18.77%) and hydrogen peroxide (24.63%) levels of maize plants. Finally, the exogenous application of tyrosine can be recommended to increase the nutrient ions, antioxidant, and osmolyte activities for better growth of maize plants growing in Cd-contaminated soils.