Influence of plant growth promoting bacteria in Helianthus annuus (sunflower) grown in Zn and Cd contaminated soils: effects on biomass production, growth parameters and metal accumulation

Pollution of the environment has increased dramatically since the birth of the industrial revolution. The off-site migration of contaminants, when not controlled, can cause serious damage on ecosystems and affect public health. These and other reasons bring up the need for new solutions of remediation, to stop the contaminants dissemination in the environmental compartments. Phytoremediation - the use of plants to remove or immobilise contaminants - may offer a low cost method for the remediation of contaminated soil. Helianthus annuus, one of the most important crops worldwide, is a plant not only with food and energy value, but also with phytoremediation potential - sunflower is a documented metal accumulator and its growth on contaminated land is thus possible. Recent studies also show that sunflower seeds of plants grown in contaminated soils do not have significant levels of metals (when compared to control specimens) and their application in biodiesel production is a possibility. The obtainment of further economic value through the valorisation of this plant species should be taken into account. Therefore the need to maximize biomass production, allowing not only to revert degraded soil, but also the further use of the biomass produced for other activities from which economical gains can be achieved, such as energy production. The use of plant growth promoting rhizobacteria (PGPR) may constitute a biological alternative to increase crop yield. The enhancement of plant growth using PGPR is documented and more recently these organisms have been used to reduce plant stress associated with phytoremediation of contaminated soils.