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

In recent years, soil contamination with heavy metals—such as plumbum, cadmium, and cobalt—has become an increasingly pressing environmental issue due to the rapid ex-pansion of industry, transportation, and urbanization. These elements are non-biodegradable, gradually accumulate along trophic chains, and can ultimately exert serious adverse effects on human health. In this study, we focused on sweet sorghum (Sorghum bicolor L.) as a promising candi-date for phytoremediation of heavy metal–contaminated soils. Both field and laboratory approaches were employed: in vitro culture of somatic cells was used to select stress-tolerant and high-yielding genotypes, while atomic absorption spectroscopy (AAS) was applied to quantify heavy metal concentrations in soil and plant tissues. Experimental results demonstrated that callus induction frequency was strongly geno-type-dependent. The highest callus formation rates were observed in Hybrid-2 (69.11%), SAB-3 (43.83%), SABB-1 (42.31%), and SAB-10 (40.32%). Among these, Hybrid-2 (27.94%) and SAB-3 (23.28%) also exhibited the highest frequencies of morphogenic callus for-mation, confirming their suitability for subsequent micropropagation and cell-based se-lection. Particular attention was paid to the distribution of toxicants among plant organs. The rate and direction of metal translocation from roots to shoots were found to critically influence the efficiency of subsequent metal removal, as stems constitute the major component of easily harvestable biomass. Nevertheless, a substantial proportion of heavy metals remained sequestered in the roots: cobalt concentrations reached 12.7 ± 1.32 mg/kg at 1 MPC (Maximum Permissible Concentration) and 16.87 ± 2.78 mg/kg at 2 MPC, accounting for more than 50% of the total accumulated amount. Similar trends were observed for cadmium (~49%) and plumbum (up to 53%). Thus, our findings underscore the pivotal role of genotype in in vitro callus formation and morphogenesis, and further highlight the potential of sweet sorghum as an effective phytoremediation agent for reclaiming heavy metal–contaminated lands, particularly in arid regions.