Acid Rain Deposition Modulates Photosynthesis, Enzymatic and Non-enzymatic Antioxidant Activities in Tomato

Acid rain is one of the serious environmental issues causing morphological and physiological changes in plants. However, the impact of acid rain to vegetable crops remains indescribable. This study explored the effects of two pH levels of simulated acid rain (SAR) on photosynthesis and activity of different enzymatic and non-enzymatic key antioxidant compounds compared with control in two different tomato cultivars. With the increasing levels of acidity of SAR, decreased significantly the plant growth, chlorophyll, carotenoids, soluble protein and soluble sugar contents in leaves of both tomato cultivars but decreased percentages were more in Red Rain than Micro-Tom cultivar of tomato. Different enzymatic antioxidant key compounds accumulation was the maximum at pH 3.5 and degraded at pH 2.5 of SAR treatment for both tomato cultivars. In contrast, the growth of hydrogen peroxide (H2O2), malondialdehyde (MDA) and proline content was increased by SAR treatment which depends on the level of pH value of SAR. In addition, marked increase in phenolic, flavonoid and reducing antioxidant activity was found at pH 3.5 followed by pH 2.5 of SAR and control in both tomato cultivars. Our findings suggested that the tomato seedlings produced more reactive oxygen species (ROS) scavenging enzymatic and non-enzymatic antioxidant compounds to SAR stress at 3.5 pH level. Meanwhile, the inhibition of growth as well as photosynthesis of tomato seedlings and the severity of oxidative damage were found at pH 2.5 of SAR which might be depend on the types of cultivar.