Absorção e redução de nitrato em duas cultivares de arroz na presença de alumínio

Abstract

Resumo -O objetivo deste trabalho foi estudar os efeitos do alumínio (Al) sobre a absorção e a redução de nitrato, em duas cultivares de arroz: Fernandes (tolerante) e Maravilha (sensível), expostas a 0 e 500 µM de Al. Depois de 21 dias de crescimento, foram determinados o comprimento, a produção de matéria seca, os teores de Al e de nitrato e a atividade in vitro da redutase do nitrato (RN), nas raízes e na parte aérea, bem como as constantes cinéticas de absorção de nitrato pelas raízes. O Al reduziu o crescimento em comprimento e a produção de matéria seca, nas duas partes das plantas, apenas da cultivar Maravilha. Os teores de Al aumentaram nas raízes e parte aérea das plantas nas duas cultivares, enquanto o teor de nitrato sofreu redução apenas nas raízes da cultivar Maravilha. A V max não se modificou, enquanto o K m da absorção de nitrato diminuiu cerca de 11% na cultivar Fernandes e aumentou 310% na Maravilha. Em presença de Al, houve redução na atividade da RN nas raízes das duas cultivares, e na parte aérea apenas da cultivar Maravilha. A cultivar tolerante foi mais eficiente na absorção e na redução de nitrato, o que indica que esses processos são importantes componentes da tolerância ao Al em arroz.Termos para indexação: Oryza sativa, nitrogênio, redutase do nitrato, tolerância ao Al. Uptake and reduction of nitrate in two rice cultivars in the presence of aluminumAbstract -The objective of this work was to evaluate the effects of Al on the nitrate uptake and reduction in two rice cultivars, Fernandes (Al tolerant) and Maravilha (Al sensitive), exposed to 0 and 500 µM Al. After 21 days of Al treatment, growth in size and dry matter yield, Al and nitrate contents and in vitro nitrate reductase activity (NR) in the tops and roots, and the kinetic constants of root nitrate uptake were determined. Aluminum reduced the growth and dry matter yield of both plant parts only in the Maravilha cultivar. Aluminum content increased in the tops and roots of both cultivars, while nitrate content decreased only in the roots of Maravilha cultivar. V max did not change, while K m of the nitrate uptake decreased in Fernandes by 11% and increased about 310% in Maravilha cultivar. In the presence of Al the NR activity decreased in the roots of both cultivars, and in the leaves of Maravilha cultivar. The Al tolerant cultivar was more efficient in nitrate absorption and reduction, wich indicates that these processes could be important components of Al tolerance in rice.

Tolerance of arabica coffee cultivars for aluminum in nutritive solution

“…Al 3+ solubility increases under pH below 5.5 and its toxicity is particularly severe under pH below 5.0 (Fageria, 1998). Justino et al (2006) found that Al 3+ has a wide range of action on plant metabolism, this probably being the reason why its mechanism of action is not well known yet. However, it is known that the negative effect of aluminum does not affect calcium absorption directly but rather through root growth inhibition, decreasing Ca 2+ absorption, regardless of the direct effect of aluminum on the absorption process (Menosso et al, 2000).…”

Aluminum in mineral nutrition of upland rice plants

“…Justino et al (2006), when evaluating P uptake and tolerance of rice cultivars submitted to Al 3+ toxicity, observed a high variability between the cultivars tested regarding the uptake capacity of P. Thus, a hypothesis can be raised that, although Al 3+ decreases the accumulation of P in the roots of Maravilha cultivar ( Figure 2D), the plants have an efficient mechanism of translocation of P to shoot. In addition to the effect of P in the interior of the plant, the existence of relationship between the availability of P and Al 3+ in the soil solution is worth mentioning, in which, while increasing the concentration of Al 3+ , the concentration of P is decreased by the formation of precipitates between the ions in question (Sousa et al, 2007).…”

“…There was also a decrease in N accumulation in the shoot ( Figure 1C). Al 3+ reduces N uptake and nitrate reductase activity (Justino et al, 2006). Most of the N is uptake by plants in the form of nitrate and the enzyme nitrate reductase acts in the first phase of the reduction of nitric N to nitrite and then to ammonia, mediated by the enzyme nitrite reductase.…”

“…There are only few studies demonstrating the behavior of macronutrient uptake in rice plants cultivated under Al 3+ toxicity (Mendonça et al, 2003;Freitas et al, 2006;Justino et al, 2006). Thus, it is important to evaluate in detail mineral nutrition of upland rice plants under Al 3+ toxicity, since macronutrient uptake is not fully elucidated and there are practically no studies addressing mineral nutrition with micronutrients.…”

Efeito do alumínio sobre compostos nitrogenados em Urochloa spp.

“…Esses resultados podem estar relacionados à resposta diferenciada da enzima redutase do nitrato, que geralmente apresenta sensibilidade ao Al +3 , como já demonstrado por alguns autores (JUSTINO et al, 2006;CRUZ et al, 2011).…”