Embryo growth alteration and oxidative stress responses in germinating Cucurbita pepo seeds exposed to cadmium and copper toxicity

Abstract

Abstract To assess the impact of heavy metals (cadmium, copper) on the germination, metabolism and growth of zucchini seedlings (Cucurbita pepo L.), a test was conducted 'in vitro' on the germination and growth of zucchini seedlings, subjected to two concentrations (100 and 200 μM) of CdCl2 and CuCl2. The germination parameters, as well as the biochemical and phytochemical properties of the embryonic axes of the seedlings, were studied. The obtained results showed that the seed vigor index (SVI) of zucchini seeds recorded a significant and remarkable decrease under the effect of Cd. A significant decrease was also noted in the length and the dry weight of the embryonic axes of the young seedlings, which differed according to the type of metal. No significant increases in malondialdehyde (MDA) and H2O2 content, or in catalase (CAT) activity were noted at the tested concentrations of the Cd and Cu salt, but very significant decreases in superoxide dismutase (SOD) activity of embryonic axis tissues were observed. Glutathione S-transferase (GST) activity exhibited a significant increase at 200 μM CdCl2 whereas the glutathione (GSH) content decreased with increasing metal concentrations (Cd, Cu) of the medium. An increase in total phenol content and antioxidant activity was recorded at 200 μM of CuCl2. Based on the obtained results, we can conclude that heavy metals (Cd, Cu) reduce the germination efficiency of zucchini seeds and cause metabolic alterations of embryonic tissue cells, and the response of zucchini seedlings to metal stress depends on the type of metal and its concentration.