Different HM (Cu, Cd, Pb, Zn, Fe, Hg, Co, Mn, Cr, Ni) of different concentrations (50ppm, 100ppm, 200ppm, 400ppm, 800ppm) was used to investigate the activity of CAT in germinating melon seeds (Citrullus lanatus and Cucumis sativus) in different interval of time 24hours, 48hours and 72hours. The HM which was obtained in form of Chlorides, Sulphates, and acetates was used to prepare solutions of different concentrations which was used to moist the melon seeds for artificial germination. Deionized water was used as the control.
The enzyme activity was estimated according to the method of Hara and Irwin (1972). It was observed that CAT activity had a significant increase when compared to the control, except with Pb for 48hours, Fe for 72hours and Cr for 72hours in C. lanatus, and Ni for 72hours in C. sativus.
The decrease in the CAT activity coursed the HM (s) at time of exposure when compared to the control indicated inhibition of the enzyme activity. It was also observed that C. sativus had high tolerance of HM induced oxidative stress more than C. lanatus, since only Ni inhibited the activity of CAT in C. sativus.