Utilização de capim-arroz (Echinochloa crusgalli (L.) P. Beauv.) para fitorremediação de cádmio evidenciado pelo speckle laser dinâmico e modificações anatômicas e fisiológicas

Abstract

In order to develop phytoremediation strategies, it is essential to know that some plants have capacity to survive and prevail in environments rich in heavy metals. However, in most cases, in order to study the structure of plants, costly and time consuming techniques are applied. Thus, this study aimed at assessing the biological activity evidenced by laser biospeckle associated with the morphology of the root tip of barnyard grass root (Echinochloa crusgalli) grown in solution with cadmium and evaluate their morphological, physiological and chemical characteristics. The seedlings of Echinochloa crusgalli were maintained for 15 days in a Hoagland and Arnon’s nutrient solution (1950) at a greenhouse. The completely randomized design was used with 8 treatments and 4 replications, 10 plants per repetition and 2 repetitions per tray. The concentrations used in the treatments were control (0); 0.01; 0.1; 0.5; 1.0; 2.0; 4.0 and 8.0 mg L-1 of cadmium as Cd (NO3) 2.4H2O. Plants of Echinochloa crusgalli from each replicate were placed in a test tube containing 150 ml of culture medium based on simple agar. The images of the speckle pattern were captured in 128 frames per root, at a 10 frame rate per second. Leaf and root samples were fixed in FAA (Formalin-Acetic-Acid-Alcohol) and 70% ethanol and then preserved in alcohol 70 ° GL. Next standard techniques for plant anatomy laboratory were used for cutting and staining sections. For each treatment, four replicates were performed and three sections per replicate were phomicrographed. The remainder was dried and homogenized for assessing the content and Cd accumulation. The dynamic speckle technique was effective to demonstrate the biological activity of E. crusgalli roots, and it is possible conclude that high concentrations of cadmium reduce the biological activity of barnyard grass. With increasing concentrations of Cd, it can be argued that growth and development of Echinochloa crusgalli are negatively affected from an initial concentration of 0.1 mg L-1. Concentrations above 1 mg L-1 modified the cortical parenchyma, aerenchyma and the endoderm formation. The species has anatomical features that contribute to their survival in the aquatic environment, contaminated with cadmium and has the potential to be used in phytoremediation programs up to a concentration of 0.5 mg L-1 Cd. In concentrations higher than 1 mg L 1 Cd, Echinochloa crusgalli are more appropriate for use as bioindicators of contamination by cadmium, due to the symptoms caused by metal.