Growth and antioxidant responses of Trigonella foenum-graecum L. seedlings to lead and simulated acid rain exposure

Abstract

Heavy metal pollution and acid rain are serious global environmental issues. The combined pollution of these two contaminants has become a new environmental issue where both stresses occur simultaneously. These abiotic stresses alter the plant growth and development, various metabolic activities and agricultural yield. However, studies on combined pollution of these remain limited. In the current study, the application of lead (Pb, 1200 mg l− 1) and/or simulated acid rain (SAR, pH 3.5) to fenugreek (Trigonella foenum-graecum L.) seedlings for 30 days resulted into various physiological and metabolic dysfunctions. Our experimental results revealed that treatments with Pb and/or SAR decreased growth attributes, membrane stability and contents of total chlorophyll and proteins, while enhanced the leakage of electrolytes, accretions of reactive oxygen species (ROS), malondialdehyde and 4-hydroxy-2-nonenal, along with lipoxygenase activity. In addition, in-gel activities of superoxide dismutase, catalase, guaiacol peroxidase and ascorbate peroxidase were seen to be amplified in Pb and/or SAR subjected tissues. Although, the activities of defensive enzymes were enhanced, they appeared to be insufficient for detoxification of overproduced ROS, consequently leading to reduced growth and enhanced oxidative stress in fenugreek seedlings. We also observed that fenugreek leaves were more sensitive to the combined treatment of SAR and Pb. However, the alone application of Pb generated comparatively more damage in roots, while leaves showed more susceptibility to SAR. In conclusion, our data suggested that the extent to which the test indexes decreased/increased in response to the combined treatment of SAR and Pb was relatively higher than in their alone applications.