Nitrate levels and stages of growth in hypernodulating mutants of Lupinus Albus. II.Enzymatic activity and transport of N in the xylem SAP

The enzymatic study and transport of N in the xylem sap was carried out with a view to observing the influence of different nitrate levels and growth stages of the plant in chemically treated mutants of Lupinus albus. Several stresses induce a reduction in plant growth, resulting in the accumulation of free amino acids, amides or ureides, not only in the shoot, but also in the roots and nodules. Although enzyme activity is decisive in avoiding products that inhibit nitrogenase by ammonium, little is known about the mechanism by wich the xylem carries these products. However, this process may be the key to the function of avoiding the accumulation of amino acids in the cells of infected nodules. The behaviour of the enzymes nitrate reductase (NR), phosphoenolpyruvate carboxylase (PEPC), glutamine synthetase (GS) and nitrogen compounds derived from fixation, such as N-Ó-amino, N-ureides and N-amide in mutant genotypes were observed. The NR enzyme was highly influenced by the application of nitrate showing much higher values than those in the non-application of nitrate, independently of genotype, being that the NR, the best evaluation period was in the tenth week. The L-62 genotype characterized with nitrate-resistance, clearly showed that the enzyme PEPC is inhibited by presence of nitrate. The L-135 genotype (nor fix) showed GS activity extremely low, thus demonstrating that GS is an enzyme highly correlated with fixation. With regard to the best growth stage for GS, Lupinus albus should be evaluated in the seventh week.

Efetividade do inoculante com Bradyrhizobium sp em diferentes substratos / Effectivenees of Bradyrhizobium sp inoculants on different substrates

Resumo: Objetivando determinar as condiçöes ideais para a sobrevivência e efetividade do Bradyrhizobium sp em substratos alternativos com diferentes potenciais matriciais, foi conduzido u experimento utilizando-se como veículo de inoculaçäo os substratos: diatomia, vinhaça, seca, vermiculita e composto urbano em relaçäo à turfa. A inoculaçäo foi procedida com a estirpe UMKL-58, selecionada em trabalhos anteriores. Os substratos foram submetidos aos m de -0,33, -1,0 e -3,00 bar e incubados por 240dias. Para a qualificaçäo dos veiculos foram feitos testes de sobrevivência da estirpe nos materiais utilizando-se os métodos de diluiçäo em placas e de infecçäo em plantas coma leguminosa cunhä (Clitoria ternatea L.) nos intervalos de 0, 12, 30, 60, 90, 120, 150, 180 e 240dias após a inoculaçäo, como também, avaliaçäo da eficiência da fixaçäo biológica do N2 em funçäo do veículo de inoculaçäo. Os resultados demonstram que o Bradyrhizobium sobreviveu melhor na diatomita submetida a m -3,0 bar e nos demais potenciais foi comparável a turfa. Para todos os veículos, observou-se que altos valores de m reduzirama taxa de sobrevivência da bactéria como também afetaram a qualidade do inóculo diminuindo a efetividade da estirpe (au)