Interação entre silício e alumínio em genótipos de batata (Solanum tuberosum L.).

Abstract

Silicon (Si) and aluminum (Al) are among the three most abundant elements in the earth's crust. The Si does not meet the requirements of an essential element for plant growth, but the beneficial effects of this element in the growth, development, yield and resistance to disease has been observed in a wide variety of plant species, while Al is recognized as being highly cytotoxic to plants and animals. There are evidences that the silicic acid aqueous interacts with Al thereby reducing its bioavailability (and so toxicity) and at the same time increases the availability of phosphorus essential element. So, the objectives of this study were to analyze the possible beneficial effect of Si, analyze the interactions between Si and Al on physiological and biochemical parameters and the possible Si potential to mitigate the toxic effects of Al in potato genotypes (Solanum tuberosum L. ssp . tuberosum) differing in Al tolerance. In the experiment to investigate the beneficial effect of Si, which defined through growth parameters, two concentrations of Si and two genotypes, four potato genotypes plants differing in Al tolerance: SMIJ319-7 and Dakota Rose (Al sensitive ), SMIF212-3 (Al tolerant) and SMINIA793101-3 (with intermediate Al tolerance), propagated in plastic cups, were grown in a nutrient solution (pH 4.5 ± 0.1) exposed to four silicon doses: 0; 0.5; 2.5; and 5.0 mM (NaSiO3). Seven days after the start of the exposure to the treatment, the plants were collected and the leaf area was determined, the number of leaves and stolons, the shoot length and fresh and dry biomass of roots and shoots. The dosage of 0.5 mM Si showed the greatest benefits to the growth of potato plants, while larger doses than 2.5 mM promoted a reduction in these parameters. Furthermore, the more responsive genotypes were SMIJ319-7 Si (Al sensitive) and SMIF212-3 (Al tolerant). For the experiments of interaction between Si and Al, potato plants of SMIJ319-7 genotypes (Al sensitive) and SIMF212-3 (Al tolerant ) were grown for fourteen days in nutrient solution (without phosphorus and pH 4.5 ± 0 , 1) exposed to combinations of two doses of Al (0 and 50 mg L-1 (AlCl3)) and three doses of Si (0, 0.5 and 1.0 mM (Na2SiO3)). After this period, leaves and roots of plants of both genotypes were collected to determine the Al concentration in the tissues, growth parameters, enzyme activity (superoxide dismutase (SOD) and guaiacol peroxidase (POD)) and lipid peroxidation. Roots of both genotypes accumulated more Al than shoot, and the Al tolerant genotype accumulated more Al than the sensitive in the roots as well as shoot. Furthermore, the presence of 0.5 mM of Si in the growth medium together with Al reduced the Al concentration in the Al tolerant roots. The exposure to Al resulted in a reduction in the length, number of root tips, surface area, the volume and number of root branches, number of leaves and leaf area of both potato genotypes, and Si alleviated the toxic effects of Al in both potato genotypes only in the number of roots and number of leaf branches parameters. In addition, the Si had a beneficial effect on the parameters number of leaves, leaf area, number of stolons in both genotypes. For biochemical parameters, there was increased activity of antioxidant enzymes and less accumulation of MDA when the plants were exposed to Si under stress of Al. From these results it is clear that the Si may be able to alleviate the toxic effects of Al due to the induction of antioxidant enzymes. So the Si has the potential to mitigate the toxic effects of Al through interactions with this metal in the plant.