Comparative Study of Citrullus Lanatus and Cucumis Sativus Defensive Mechanism against Oxidative Stress Induced by Heavy Metals

Fruits are integral parts of human diets that supply vitamins, minerals, boost metabolic functions and strengthen the immune system to enhance human productivity. Hence fruits contain antioxidants and phytochemicals that protect the body from cell and tissue damages that could be induced by reactive oxygen species and also act aas hormones that protect the plant from predators. They further function as prophylactic agents against morbidity cases or chronic diseases and in the growth and development of plants. The purpose of this study is to compare the relative potentials of two species of Citrullus lanatus and Cucumis sativus in inhibiting oxidative stress induced by some selected heavy metals. Heavy metals (HM) like Lead (Pb), Mercury (Hg), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Manganese (Mn), Nickel (Ni), Iron (Fe), Copper (Cu) and Zinc (Zn) obtained in different forms; chlorides, sulphates, nitrates and acetates were used to prepare solutions of different concentrations 50ppm, 100ppm, 200ppm, 400ppm and 800ppm. Two species of melons seeds C. lanatus and C. sativus were subjected to artificial germination by sprinkling different concentration of different HM on the melon seeds to induce oxidative stress on the germinating seeds, while deionized water was used as control. Oxidative enzyme activities like catalase(CAT) and superoxide dismutase (SOD) were estimated according to Hara and Irwin (1972) method, poly phenol oxidase (PPO) was estimated using a simple method describe by Esterbauer, Schwarzl and Hayn (1977). The activities of the enzymes were checked at interval of 24hours, 48hours and 72hours of exposure. It was observed that HM induced oxidative stress triggered the release of oxidative enzymes and inhibits the enzyme at some concentration at a given period of exposure. The inhibition account for the toxicity of the heavy metal which lead to death of the enzyme, while high enzymatic activity account for tolerance. The two melon species were compared base on their tolerance to HM induced stress, it was observed that defensive mechanism against HM induced stress varied due to specie difference. These could be as a result of oxidative enzyme efficiency or insufficiency between the two species. Therefore Cucumis sativus had more increased tolerance than Citrullus lanatus. Cucumis sativus (Cucumber) is likely to survive in HM polluted farm land more than Citrullus lanatus (water melon).