In search of the exclusion/low-accumulation mechanisms: Cadmium uptake and accumulation from soil by cultivated (Solanum melongena L.) and wild eggplants (Solanum torvum L.)

Abstract

The use of Cd-excluding cultivars on the most widespread soils moderately polluted with Cd is a sustainable solution for the safe agricultural production. In order to explore the defense mechanisms and differences in the cadmium (Cd) uptake from soils and accumulation in plant tissues between low-accumulator and excluder plants, Cd concentrations/loads in plant tissues and impact on plant growth and physiological properties (photosynthetic characteristics, antioxidant enzymes and related indices) of the cultivar Solanum melongena Liaoqie No.3 (SML) and the wild species Solanum torvum (STO) grown in soils containing from 0.24 to 18.61 mg kg−1 Cd (i.e. from the natural Cd content through moderate to high pollution level) were studied in the pot experiments carried out under natural light conditions. It was found that the major protective barrier in the more sensitive to Cd toxicity excluder species (STO) was a root system accumulating 2-3-fold lesser Cd loads through the induction of dehydration/drought stress than a more Cd-tolerant low-accumulating plant (SML). A supportive defense mechanism appeared to be a reduced Cd enrichment of a xylem sap and its increased flow rate during long-distance transport from roots to leaves, occurring in the both types of plants, but with a lesser intensity in a more Cd-tolerant low-accumulating species. Due to maintaining plant-specific Cd-adaptive level, growth and biomasses of both species were basically the same, while due to the considerably lower Cd accumulation, photosynthetic parameters were higher in Cd-excluder STO species, and the amounts of lipid peroxidation (MDA) and free proline were higher in Cd low-accumulating SML cultivar. Concurrence of Cd and drought-resistance mechanism and better physiological parameters in Cd-excluder suggest promotion of this mechanism in cultivars under the climate change conditions.