Formação de aerênquima radicular e redução da toxicidade pelo cádmio em plantas de milho saracura submetidas ao óxido nítrico

Abstract

The work aimed to evaluate the formation of root aerenchyma and reduction of cadmium toxicity in saracura corn plants submitted to nitric oxide. Saracura corn plants were subjected to permanent flooding for 30 days. Weekly, cadmium nitrate solution was applied Cd (NO3)2 to 0; 10μM; 50μM, and sodium nitroprusside Na2 [Fe (CN) 5NO].2H2O as a 0.5 μM nitric oxide (NO) donor; 0.1 μM; 0.2 μM. To ensure seedling nutrition, a nutrient solution (Hoagland and Arnon, 1950) was applied weekly at 40% of the ionic strength. Root biometrics, indicators of oxidative stress, hydrogen peroxide H2O2 and malondialdehyde MDA, enzymes of the CAT catalase-hydroperoxidase antioxidant system, superoxide dismutase SOD, ascorbate peroxidase APX were analyzed. In addition, root anatomical analyzes. As well as, growth analysis, leaf gas exchange and leaf anatomical analysis. Semi-permanent blades with root cross sections and median leaf region, paradermic sections of the leaf, were made and subjected to the usual plant microtechnical procedures. The slides were observed under an optical microscope with an image capture system attached, the photomicrographs were analyzed using the UTHSCSA-ImageTool software. The evaluated parameters were: epidermis thickness, cortex thickness, cortex proportion, endoderm thickness, xylem vessel diameter and vascular cylinder proportion, mesophyll area, mesophyll thickness, abaxial and adaxial epidermis thickness, bundle area vascular, diameter of xylem vessels, polar and equatorial diameter of stomata, stomata functionality, stoma density, stoma index and stoma cell density. The experimental design was completely randomized in a 3x3 factorial scheme with five replications. The data were subjected to analysis of variance and the Scott-Knott test for p <0.05. However, in root biometry only fresh mass had interaction between treatments, although the oxidative stress indicators H2O2 did not interact, but a gradual drop was observed in higher concentrations of NO, however, MDA showed interaction in concentrations of Cd. In the activity of antioxidant enzymes, SOD reduced in higher concentrations of NO, while CAT was observed interaction in the treatments of Cd and NO. Although, in the root anatomical analyzes, the root cortical aerenchyma, thickness of the epidermis, thickness of the cortex, proportion of the cortex, thickness of the endodermis, diameter of xylem vessels and proportion of the vascular cylinder showed interaction between the treatments of Cd and NO. However, higher concentrations of Cd and NO reduced the total dry mass, leaf and stem dry matter, however, root biomass allocation increased. However, there was an increase in gas exchange at higher concentrations of Cd and NO. Although, lower concentrations of Cd and NO, an increase in the analyzed anatomical variables was observed, however, in higher concentrations these variables were reduced. Consequently, NO has developed a role as a molecule antagonistic to Cd, decreases the concentration of H2O2, by reducing the activity of SOD and increasing CAT. H2O2 is directly linked to the formation of aerenchyma. However, NO in low concentrations decreased the toxicity of Cd and physiological and anatomical characteristics similar to Cd-tolerant plants. Higher concentrations of NO may contribute to negative effects or toxicity in saracura corn plants.