Germination and the Biochemical Response of Pumpkin Seeds to Different Concentrations of Humic Acid under Cadmium Stress

The poisoning of heavy metals and their accumulation in food chains are major environmental and health risks. There have been several reports that determined that pumpkins tend to collect small amounts of nitrate or heavy metals. Therefore, the aim of the present study is to investigate the effect of organic matter (humic acid) on the germination and activity of antioxidant enzymes, glycosylate cycle enzymes, and utilization of lipid and protein reserves of pumpkin seeds under cadmium stress conditions. An experiment was conducted to quantify the germination response and biochemical change of pumpkin seeds to the use of humic acid under cadmium stress conditions. The treatments were cadmium at three levels (0 (control), 100, and 200 mg.L⁻¹) and humic acid at five levels (0 (control), 100, 200, 300, and 400 mg.L⁻¹). Linear and sigmoidal models were used to investigate the trend of trait changes. The results show that changes in the germination percentage and seed vigor were affected by applying humic acid and cadmium stress. The highest germination percentage for pumpkins was observed without stress and cadmium stress at a concentration of 200 mg.L⁻¹. The results of quantification for the germination and seed vigor also showed that the model of germination changes by the use of humic acid was sigmoidal in non-stress and cadmium stress conditions of 100 mg.L⁻¹, but it was linear for seed vigor in the stress conditions of 200 mg.L⁻¹. The activity of superoxide dismutase, catalase, peroxidase, isocitrate lyase, and malate synthase was also affected by the simultaneous use of humic acid and cadmium stress, and the trend of their changes was linear.