Lead tolerance, accumulation and translocation in two Asteraceae plants: Limbarda crithmoides and Helianthus annuus

Abstract

• Limbarda crithmoides L. and helianthus annuus L. plants morphology has not been affected under effect of lead (Pb) with the exception of height reduction in some Pb applied concentrations. • According to the metal tolerance index, limbarda crithmoides was more tolerant to Pb induced stress than helianthus annuus . • High levels of Pb were detected in the above-ground parts. • The concentrations of the accumulated Pb were higher in the roots of limbarda crithmoides and helianthus than in the shoots of these species. Lead (Pb) is known as a toxic metal and a non-essential element for plant metabolism and growth. This work investigated the phytotoxicity of Pb induced stress and assessed the accumulation potential of Pb in two Asteraceae plants; Limbarda crithmoides and Helianthus annuus. The experiments were performed for 45 days using different concentrations of Pb (0, 100, 200, 300 and 500 µmol.L –1 ). The dry biomass production in shoots and roots of Limbarda crithmoides were significantly enhanced with the increase of Pb doses in the growth medium, Helianthus annuus plants showed a modest variation in shoot and root dry weights, but without any significant difference as compared to the untreated plants. In addition, metal tolerance index values determined in the shoots and roots of these two species followed a similar trend as the dry weight contents. Both phenolic compounds and flavonoids were significantly increased in the two Pb treated species in comparison to the untreated plants (except flavonoid content of Limbarda crithmoides roots). Total inorganic nitrogen and macronutrient uptake were also assessed, and the two species showed different behaviour when varying Pb concentrations. Moreover, the two species accumulated Pb in their roots more than in the shoots (less than 1000 µg.g –1 DW) with a low translocation from roots into shoots (translocation factor < 1). Our findings demonstrated that both Limbarda crithmoides and Helianthus annuus were tolerant to Pb stress; nonetheless, the two species could not be classified as Pb hyperaccumulators.