Responses of Hydroponically Grown Sorghum (Sorghum bicolor L.M) to Zinc (Zn) Stress
Abiotic stress especially due heavy metals is one of the major environmental problems that threatens food security and pose greater risks to human health worldwide. In this research, greenhouse hydroponic experiments were carried out to study the morphological and biochemical responses of Sorghum bicolor L.M to different Zinc (Zn) levels. Two-week-old seedlings transplanted in hydroponic solutions were treated with different doses of Zn in the concentration ranges of 5, 25, 50, 100 and 200 mg/L supplied as ZnSO4. 5H2O. After 21 day of culture, the plants were harvested, blotted to dryness and separated into roots and shoots. The root and shoot lengths, dry weights and non-enzymatic biochemical parameters such as proline, Chlorophyll a, b, Carotenoids (pigments) were determined. The results indicate that Zn applications significantly (P<0.05) depressed the lengths of root and shoot, dry weights and pigment contents compared to untreated plants (control). The effects were more pronounced with increased Zn dosage. The accumulation of the metal and proline contents in treated plants however, increase gradually with increasing Zn concentrations (P<0.05). The changes in these parameters had resulted in toxicity symptoms and overall growth retardation especially at elevated concentrations and the estimated critical toxicity thresholds in both solution and tissue concentrations suggest that sorghum bicolor L.M should not be grown beyond Zn concentration of above 3.2 mg/L.