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AbstractAbstract
[en] Three experiments were conducted under controlled conditions with the objectives of evaluating the effect of different concentrations of phosphorus and on the presence of other ions on the kinetic of absorption. Excised roots of rice and bean were placed in aereated solutions containing increasing concentrations of NaH2PO4 (10-7 M to 5x10 -2M) during 90 minutes. The rate of absorption (v = umols P/g dry matter) and the kinetic constants Vmax and Km were determined. Similar procedure was used to to evaluate the interaction of Mg+2, Al+3, K+, N-NH4+, N-NO3- and N-ureia in the uptake of phosphorus during 120 minutes. In another experiment, the effect of the presence of Mg+2 and/for Al+3 in the uptake and redistribution of phosphorus, was evaluated by varying the external concentration (1 ppm, 5 ppm, 10 ppm and 20 ppm) during a period of 17 hours, and utilizing whole rice plants. It was observed a dual mechanism, with two phases following the Michaelis-Menten kinetics and with transition phase 1 - 50 x 10-5 M. The best explanation of the experimental data was obtained, by transforming the data in accordance with HOFSTEE (1952). Bean was more efficient than rice in the first phase of uptake (higher Vmax). Al3 had a clear stimulatory effect on the uptake of phosphorus, promoting, however, the anion fixation in the root at lower concentrations. At the highest concentrations (20 ppm) of phosphorus this effect was not evident. No effect on the uptake was observed with Mg+2, K+ and different forms of nitrogen. Urea could have a depressive effect although, not significant. Possible mechanisms involved are discussed. (author)
[pt]
Objetivando caracterizar os efeitos das diferentes concentracoes de fosforo e da presenca de outros ions na cinetica de absorcao de radiofosforo, foram conduzidos ensaios em solucao nutritiva, em condicoes ambientais controladas. Foram empregadas raizes destacadas de arroz e feijao para os estudos com diferentes concentracoes de fosforo no meio (10-7 M ate 5 x 10-2 M) e para avaliar as interacoes promovidas por Mg+2, Al+3, K+, NH4+, N-NO3-, N-ureia no mecanismo de absorcao por periodos de uma hora e meia a duas horas. Em plantas inteiras de arroz procurou-se avaliar os efeitos da presenca de Mg e/ou aluminio na absorcao e transporte de fosforo quando variava a concentracao externa (1 ppm, 5 ppm, 10 ppm e 20 ppm) por um periodo de 17 horas. Foi constatado um mecanismo duplo de absorcao com as duas fases seguindo a cinetica simples de Michaelis-Menten, e com ponto de transicao entre 1-50x10-5. A transformada de dados segundo Hofstee adaptou-se melhor a interpretacao dos dados experimentais. Feijao foi mais eficientes na absorcao que arroz para a primeira fase (maior Vmax). Aluminio apresentou efeito estimulatorio nitido na absorcao de fosforo, promovendo porem, a fixacao do anion na raiz quando consideradas as concentracoes mais baixas. Em concentracoes altas de P, este ultimo efeito nao foi evidenciado. Magnesio nao promoveu maior absorcao, nem maior transporte do que K+; o mesmo aconteceu com as diferentes formas de nitrogenio. Ureia poderia ter um efeito depressivo maior, embora nao significativo. Discutem-se os provaveis mecanismos envolvidos nestas respostas. (autor)Original Title
Estudos sobre a cinetica de absorcao do fosforo pela arroz (Oryza sativa L.) e pelo feijoeiro (Phaseolus vulgaris L.)
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Anais da Escola Superior de Agricultura 'Luiz de Queiroz'; ISSN 0071-1276; ; CODEN AESQA; v. 44(2); p. 1503-1561
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