Optimization Of The Nitrate Reductase Activity Assay For Citrus Trees

The aim of this study was to assess factors that can affect the in vivo and in vitro assays of the nitrate reductase activity (NRA) in sweet orange trees and then standardize conditions for tissue sampling and analysis. Seven-month-old plants grown in pots were used, of which, mature and healthy leaves between the third and the fifth position from the branch apex, stems, and roots were assessed. One half of each leaf was used for in vivo tests, and the other half was used for in vitro tests. In addition to varied incubation time and temperature, in vivo KNO3and n-propanol concentrations and in vitro KNO3and NADH concentrations were evaluated. The optimum conditions for the in vivo NRA assay in leaves were: 200 mmol L−1KNO3and 1 % n-propanol at 40 °C for 20 min. The highest leaf NRA occurred at 11:00 h for the in vivo assay and at 13:00 h for the in vitro assay, with both analysis showing similar results. Overestimation of the in vitro NRA occurred as compared to the in vivo analysis when accessed early morning and late afternoon. Branches bearing fruits show reduced NRA in young mature leaves, whereas sprouting significantly increases NRA in correspondent leaves. For the root assays, the optimized conditions for the NRA estimation were the same as for leaves. Although roots and stems (bark) have shown some NRA, it was six times lower than leaf NRA. 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Caracterização química e mineralogia de solos antrópicos (terras pretas de índio) na amazônia central

Na Amazônia brasileira é comum a ocorrência de sítios arqueológicos. Frequentemente, observa-se que as ações humanas nesses sítios promoveram modificações significativas em muitas das características físicas, morfológicas e químicas dos solos desses ambientes, tornando-os muito diferentes dos solos adjacentes, especialmente nas áreas de terra firme da região. Embora muitos estudos tenham sido conduzidos visando compreender a magnitude dessas modificações e seus reflexos na gênese dos solos influenciados, muitas questões precisam ser mais bem compreendidas, sobretudo as relacionadas com a mineralogia desses solos. Este estudo teve como objetivo avaliar as características químicas, a composição mineralógica das frações argila e areia e o grau de pedogênese de cinco perfis de solos com horizonte A antrópico (Au), em ambientes de terra firme e várzea, localizados na Bacia Sedimentar do Amazonas, entre Coari e Manaus-AM. Amostras de solos foram coletadas, preparadas e submetidas às análises químicas de rotina e caracterizadas quanto aos teores de carbono oxidável e aos teores de Si, Fe, Al e P; adicionalmente, efetuou-se a identificação dos minerais presentes nas frações argila e areia, por meio de difratometria de raios X. Os resultados mostraram que as modificações promovidas pela atividade humana levaram à melhoria da fertilidade do solo, resultando em solos com acidez moderada, elevados teores de Ca2+ e de P disponíveis e baixos teores de Al3+ trocável. Esses resultados também revelaram teores muito elevados de P-total nos horizontes antrópicos, variando entre 1.630 e 8.840 mg kg-1 de P2O5. A mineralogia da fração argila dos solos antrópicos de terra firme revelou dominância de caulinita, além da ocorrência de gibbsita, de goethita e de óxidos de titânio (anatásio). O perfil de várzea, além de caulinita e goethita, apresentou também minerais do tipo 2:1 na fração argila. A mineralogia da fração areia dos solos estudados revelou dominância de quartzo, independentemente do ambiente. A fração magnética é composta por maghemita e hematita. Constatou-se, portanto, significativa riqueza química nos horizontes antrópicos, bem como diferenças na composição mineralógica desses horizontes