Silício como amenizador da toxicidade de cádmio em alface

Abstract

Lettuce plants have been widely used as a model for toxicity tests, mainly because they are sensitive when exposed to stresses, such as Cadmium (Cd) contamination. To contain the advance of contamination by this metal, softeners are used, such as silicon (Si), which has been shown to be an excellent attenuator of the toxicity of metals. Thus, the objective was to evaluate the potential of silicon on the physiological and biochemical variables of plants of different lettuce cultivars grown under cadmium toxicity. An experiment was carried out with seed germination and seedling performance of lettuce cultivar Veneranda. Intact seeds were subjected to hydropriming and silicon priming and placed to germinate on paper moistened with the presence (1 mM) and absence (0 mM) of Cd. The results showed that in the presence of Cd, silicon priming contributed to minimize the effects of this metal, and the final percentage of germination was not affected, since in the absence of this metal, priming with Si promoted an increase in the speed of this process. An experiment was also carried out in a hydroponic system with two commercial lettuce cultivars: Veneranda and Rubinela. The seedlings were taken to the NFT (Nutrient Film Technique) hydroponic system with recirculating nutrient solution, and after acclimatization the following treatments were added: T1 (nutrient solution); T2 (nutrient solution + 2,500 μM of Si); T3 (nutrient solution + 0,5μM of Cd); T4 (nutrient solution + 0,5 μM of Cd + 2,500 μM of Si), the morphophysiological and biochemical variables were evaluated in this experiment. The presence of Cd negatively affected all the variables evaluated in the present thesis, causing chlorosis and anatomical changes observed in the roots and shoots. Si, when added to Cd, had a mitigating effect on the toxicity of this metal, promoting better results in all these variables. Thus, we can conclude that Cd had a negative effect on plant growth, while the addition of Si alleviated the stress caused by Cd. There is potential for Si to mitigate the toxicity of Cd in lettuce, and can be used to increase productivity and quality of this vegetable, which is of great importance and is consumed worldwide.