Morpho - Physiological Responses of Sunflower (Helianthus annus L) Exposed to Lead and Cyanide Stress

The term "hyperaccumulator" refers to a group of plants from different families that can grow in soils with high levels of metals and accumulate unusually large amounts of heavy metals in their above-ground parts. This research examined the growth responses, accumulation capacity, and physiological mechanisms of sunflower plants subjected to lead and cyanide stress simulated by laboratory-grade sodium cyanide (NaCN) and lead oxide (PbO3) at different concentrations:(sodium cyanide = 100, 50, 25, and 0 mg/L; lead oxide = 500, 200, 100 and 0 mM, respectively). Seedlings (4 weeks old) were spiked once with 100 mL of their respective lead and cyanide solutions, and the response of the sunflower plants was monitored weekly for 2 weeks. The experiment was replicated 3 times and observed weekly for 2 weeks. Non-destructive leaf spectroscopy and root and shoot biomass and lead content of the plants were evaluated. The results revealed that both lead and Cyanide significantly (p<0.005) reduced sunflower root and shoot biomass with increasing concentrations. The results revealed that lead significantly (p<0.05) reduced plant height, leaf number, and shoot and root biomass. The control had the highest plant height of 35 cm, while the 500 mM treatment had the shortest length of 25 cm. Moreover, the control had the highest biomass of 13.2g and 3.5g, respectively, while the 100 mM treatment had the lowest biomass of 10.8g and 1.1g for shoot and root, respectively. The lead (Pb) concentrations in the shoot of sunflower significantly (p<0.005) increased with increasing concentrations, with the highest content (0.478 mg/kg) observed in the 500 mM treatment, while the control (0 mM) had the lowest (0.006 mg/Kg) lead concentrations. Lead uptake in the roots showed that the 500 mM treatment had the highest lead content (0.515mg/Kg), while the control (0 mM) had the lowest (0.006mg/Kg). In the cyanide-treated groups, the control (0 mg/L) had the highest plant height (70cm), while the 100 mg/L treatment had the lowest (57 cm). The leaf spectroscopy results showed that the anthocyanin reflectance index (ARI) and chlorophyll A and B were significantly different (p<0.05) across the different lead and cyanide treatments. Total chlorophyll did not differ significantly (p>0.05) among the sunflower plants treated with different concentrations of Lead. Overall, Sunflower showed differential response and uptake of varying concentrations of lead and Cyanide. Therefore, sunflowers can serve as sentinels for heavy metal- and toxin-polluted soils and be good candidates for cleaning them. The study concludes that higher concentrations of heavy metals are harmful to plant growth,