Integrating Biochemical, Morpho-physiological, Nutritional, and Productive Responses to Cd Accumulation in Massai Grass Employed in Phytoremediation

Abstract

Cadmium (Cd) phytoextraction efficiency basically depends on Cd accumulation in their tissues. Thus, our aim in this study was to select biochemical, morpho-physiological, nutritional, and productive responses associated to Cd accumulation in the roots, stems and sheaths, and leaf blades of Panicum maximum cv. Massai (Massai grass), using the random forests analysis. Massai grass was exposed to combinations of three sulfur (S) concentrations (0.1, 1.9, and 3.7 mmol L−1) and two Cd concentrations (0.0 and 0.1 mmol L−1) in nutrient solutions. The dry biomass production of Massai grass exposed to Cd decreased by around 50% in relation to control. However, there were no visual symptoms of Cd toxicity in the shoot of this plant, even with Cd concentrations in their shoot exceeding 100 mg kg−1 DW. The lowest dry biomass production of the plants exposed to Cd combined with the absence of visual symptoms of Cd toxicity indicates us that Massai grass is a bioindicator plant that can greatly cope with the Cd-induced stress, but in a little bit different way from other plants. Antioxidant enzymes apparently are not essential for Massai grass cope with Cd-induced stress, differently of other mechanisms (e.g., higher synthesis of thiol compounds and amino acids involved on reactive oxygen species (ROS) scavenging and Cd chelation). Probably, the plant responses that most explained Cd accumulation in Massai grass can be used to identify grasses with high capacity to accumulate Cd in phytoremediation programs with this group of plants.