Metabolismo do nitrogênio, carbono e antioxidante em plantas jovens de seringueira (Hevea brasiliensis) na presença de cádmio e alumínio

Abstract

The rubber tree (Hevea brasiliensis) is the largest source of natural rubber in the world, a product widely used in pneumatic manufacturing and in a large manufactures number. However, there is little information on the rubber trees tolerance in relation to heavy metals. Thus, the objective in this study was to evaluate the physiological variables of nitrogen and carbon metabolism, as well as antioxidant metabolism, both in leaves and roots of young rubber plants cultivated in nutrient solution in the presence of Cadmium (Cd) and Aluminum (Al). The experiment was conducted by hydroponic cultivation. Thirty days after germination, the seedlings were conditioned in nutrient solution of Bolle -Jones. Increasing concentrations of Cd: 0, 20 and 40 mg/L; Al: 0, 15 and 30 mg/L, were used to evaluate the metabolic behavior. The variables analyzed were: liquid photosynthesis (A), stomatal conductance (gs) and transpiration (E), chlorophyll and carotenoid content, biomolecules (total soluble sugars, reducing sugars, amino acids and proteins), antioxidant metabolism enzymes: Peroxide dismutase (SOD), Catalase (CAT) and Peroxide Ascor bate (APX); nitrogen assimilation enzymes Nitrate Reductase (NR) and Glutamine Synthetase (GS), in addition to the presence of macro and micronutrients. After 75 days of treatment induction, the plants submitted to Cd concentrations had the lowest values of A throughout the experimental process with behaviors up to 10 times lower than the control (0.89 μmol CO2 m -2 s -1 ) , this resulted in a lower biomolecules formation including the formation and enzymes activity of N metabolism, but with higher enzymes activity of the antioxidant system, both in the leaves and in the roots. The NR in the roots, presented low activity in the treatments with Cd (20 and 40 mg/L), the GS activity in leaves was lower in the treatments with Cd and 15 mg/L of Al. In general, Cd and Al traits in rubber plants decreased the macronutrient content in the roots, especially the N, Ca, and S elements. Fe and Mn contents were higher in the Cd presence and P levels were higher in the roots in the Cd and Al presence. There was a greater macronutrients presence in leaves in all treatments, but the micronutrients presented their high concentration in the root system, but with a higher Fe presence in the treatments with Cd. These results suggest a negative Cd influence in the two concentrations, in the C and N metabolism, acting more drastically than Al.