VARIED RESPONSES TO HEAVY METAL (Cd AND Pb) STRESS ON THE GROWTH AND DEVELOPMENT OF Cucumis melo L. (Melon) PLANTLETS

Toxic compounds such as heavy metals can cause damage to plants by altering major plant physiological and metabolic processes. In addition, these compounds are considered the most important soil pollutants. Soil metals are strongly absorbed on the root and transported to the plant, affecting their growth and development. In the present study the effects of increasing concentrations of cadmium (Cd) and lead (Pb) on seed germination and on seedling growth of melon (Cucumis melo L.) cv. Honeydew were evaluated. Melon seeds were exposed for 9 days to 0, 5, 15, 20, or 25 mg/L of Cd or 0, 50, 100, 150, 200, or 300 mg/L of Pb, respectively. Germination and root and stem growth were recorded daily. At the end of the exposure time, the Cd and Pb concentrations in the plantlets were determined. There were no effects of Cd or Pb on seed germination. Pb inhibited the growth of the roots and stems, whereas Cd induced an increase in the latter. Both Cd and Pb accumulations in plantlets increased gradually with increasing heavy metal exposure. Seedlings were able to tolerate 0.5 mg/g of Cd in tissues. At a given concentration of plant tissue, Pb was more toxic than Cd.