Phytoremediation of Heavy Metal-Contaminated Soil Using Drought-Adapted Sweet Sorghum (Sorghum bicolor L.) in Arid Regions of Kazakhstan

Soil contamination with heavy metals is a persistent challenge in the arid regions of Kazakhstan. This study evaluates the phytoremediation potential of sweet sorghum (Sorghum bicolor L.), a drought-tolerant crop with a well-developed root system, using a combination of in vitro and analytical approaches. In vitro culture of somatic cells revealed clear genotype-dependent differences in callus induction and morphogenesis, with Hybrid-2 and SAB-3 exhibiting the highest regenerative capacity and thus the greatest suitability for further biotechnological improvement and stress-tolerance selection. Analysis of metal distribution, based on atomic absorption spectroscopy (AAS), demonstrated that S. bicolor predominantly retained Pb, Cd, and Co in the root system. Cobalt accumulated to 12.7 ± 1.32 mg/kg under 1 MAC and 16.87 ± 2.78 mg/kg under 2 MAC, accounting for more than half of the metal absorbed by plants. Cadmium showed a similar root-dominant pattern, whereas lead exhibited the lowest mobility and remained almost entirely sequestered in roots, with translocation factors consistently below unity (TF < 1). Overall, these findings confirm the suitability of sweet sorghum as an environmentally sustainable species for the phytostabilization of Pb-, Cd-, and Co-contaminated soils in arid environments and highlight the value of genotype pre-selection under stress conditions for optimizing phytoremediation performance.