Mechanisms of the internal structure and operation of Panicum aquaticum in response to arsenic

Abstract

Due to the high toxicity of arsenic, many studies have attempted to improve the techniques for its removal from the environment, using methods such as phytoremediation by tolerant species. To evaluate the tolerance of Panicum aquaticum to contamination by arsenic, both physiological and anatomical evaluations were conducted. The plants were grown in Hoagland and Arnon nutrient solution in a greenhouse for 30 days under six concentrations of arsenic: 0.00, 0.25, 0.50, 1.00, 2.00, and 4.00 mM. Analyses of growth, gas exchange, the anatomy of leaves and roots and of the activity of antioxidant system enzymes were conducted. The relative growth rate, specific leaf area and leaf area ratio were modified in the presence of arsenic. Gas exchange was not affected. The leaf anatomy showed reductions in the epidermal thicknesses on the abaxial face, on the blade and on the chlorenchyma; increases in the set of bulliform cells, in the cuticle thickness and in the area of the sclerenchyma; reductions in the number and distance of vascular bundles; an increase in the stomatal index; an increase in the stomatal functionality only on the adaxial face of the epidermis; and reductions in the number and density of stomata. The roots presented reductions in the thicknesses of the epidermis, endodermis and exodermis and modifications in the Carlquist vulnerability index. Only the catalase activity was affected, showing an increase at the lowest concentrations followed by a decrease at higher concentrations. P. aquaticum proved partially tolerant to arsenic at the lowest concentrations and presented evidence of toxicity at the highest concentrations.