Evaluation of Physiological and Biochemical Parameters and Some Bioindicators of Barium Tolerance in Limbarda crithmoides and Helianthus annuus

Soils and water resources of our ecosystems may contain Barium (Ba), a toxic metal naturally existent in the Earth’s crust and also can be derived from recycled wastes produced of several anthropogenic activities. As a result of this fact, the accumulation of Ba in agriculture soils would increase to reach the crops and eventually end up in the human food chain. The purpose of this work was to study tolerance and accumulation abilities in Limbarda crithmoides and Helianthus annuus treated with increasing concentrations of barium (from 0 to 500 µM) for 45 days. In order to evaluate the response of these species to Ba stress, the biomass production, the water status, and the accumulation of the secondary metabolites, macronutrients, total inorganic nitrogen (TIN), and Ba in shoots and roots, as well as chlorophyll levels, and metal tolerance index of the entire plant were assessed. Results showed an increase in plant biomass production and tolerance index in the two species with increasing Ba concentration. A significant increase in polyphenols and flavonoids levels was also shown with no negative effect on the macronutrients and TIN; however, the latter were found reduced in roots of L. crithmoides. Chlorophylls also were not affected. An average of 3000 µg·g−1 DW of Ba was accumulated in each organ of L. crithmoides while H. annuus accumulated up to 1350 µg·g−1 DW in the shoots. Our findings proved that L. crithmoides and H. annuus were susceptible to tolerate Ba-induced stress with high levels of Ba accumulation in the aboveground parts as well as in the roots during the 45 days of the experiments.