Toxic Effect of Nickel (Ni) on Growth and Metabolism in Germinating Seeds of Sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.)

To assess the toxic effect of nickel (Ni) on the growth and some key metabolic processes in sunflower, varying levels of Ni as Ni(NO₃)₂ up to 60 mg L⁻¹ were applied once to sunflower cultivars SF-187 and Hysun-33 at sowing time in sand culture. An increase in Ni in the growth medium adversely affected growth parameters, sugar concentration (both reducing and non-reducing), as well as the activities of α-amylase and protease. It also slowed down mobilization of stored proteins and amino acids in the germinating seeds. However, an increase in the activities of α-amylase and protease was observed over time from 24 to 120 h after sowing. Cultivar Hysun-33 showed better performance than SF-187 in the presence of excess Ni. Overall, Ni-induced reduction in germination of sunflower seed appeared to be due to disturbance in biochemical metabolism as the availability of sugars for the synthesis of metabolic energy as well as necessary amino acids for the synthesis of proteins and enzymes essential for the growing embryo are generally reduced due to suppression in α-amylase and protease activities.