The main purpose of this study was to investigate the seasonal variation of copepod community structure during the months of July, September and November 2003 (dry season) and January, March and May 2004 (rainy season) in the Curuçá estuary, northern Brazil. Samples were collected during neap tides via gentle 200μm mesh net tows from a small powerboat. Measurements of surface water conductivity were accomplished in situ using an electronic conductivimeter and salinity was later obtained through the transformation of the conductivity values. Salinity varied seasonally from 7.2 ± 0.1 to 39.2 ± 1.8 (mean ± standard deviation) and was influenced mainly by differences in the amount of rainfall between the studied sampling seasons. In total, 30 Copepoda taxa were identified and Acartia tonsa comprised the most representative species throughout the entire studied period followed by Acartia lilljeborgii, Subeucalanus pileatus and Paracalanus quasimodo. In the present study, the density values, ecological indexes and copepod species dominance presented a clear seasonal pattern, showing that the studied area may be considered seasonally heterogeneous in relation to the investigated parameters.

This study was carried out to establish comparative effects of drought and recovery on the nitrate assimilation and nodule activity related to N 2 fixation in cowpea plants [Vigna unguiculata L. (Walp.)] previously inoculated with Bradyrhizobium spp. BR-3256 (CB-756) strain in the presence of 5 mol m -3 NO -3 . Twenty-eight-day-old nodulated plants were submitted to water deprivation during 4 consecutive days and afterwards resupplied with nutrient solution during 2 days. The water deprivation caused a rapid increase in the nitrate content in root and a marked reduction in leaf nitrate reductase (NR) activity. In contrast nodule NR activity was slightly increased by water deprivation. Concomitantly, in nodules of water stressed plants, leghemoglobin and glutamine synthetase (GS) activity declined and a progressive reduction in ureide-N concentration in xylem sap was observed. Leaf-NR activity increased rapidly after rehydration while leaf nitrate content declined. In contrast both GS activity and soluble protein content in the nodule continued to decline in rewatered plants. In addition the concentration of leghemoglobin recovered well, while the xylem ureide-N content experienced a slight increase after rehydration. Despite the nitrate assimilation in leaves and the nodule activity had been both severely affected by water stress, the rapid recovery of nitrate reductase activity suggests that the nitrate assimilation process is less sensitive to drought/rehydration cycle when cowpea plants are nodulated in presence of moderate nitrate level.

No abstract

The present work was carried out to verify the occurrence and distribution of Cymbasoma longispinosum Bourne, 1890 in a tropical Amazon estuary from North Brazil. Samplings were performed bimonthly from July/2003 to July/2004 at two different transects (Muriá and Curuçá rivers) situated along the Curuçá estuary (Pará, North Brazil). Samples were collected during neap tides via gentle (1 to 1.5 knots) 200 μm-mesh net tows from a small boat. Additional subsurface water samples were collected for the determination of environmental parameters. Males and females of Cymbasoma longispinosum were only observed during September and November/2003. The highest number of organisms was found in September/2003 at the Muriá River transect. The presence of C. longispinosum in samples obtained during September and November/2003 could probably be related to the reproductive period of this species in the studied estuary, which is directly related to the dry period in the region. The highest salinity values and the highest number of individuals observed in September/2003 corroborate with the previous assumption, since no C. longispinosum was found during the months comprising the rainy period (January to June).
O presente trabalho foi desenvolvido para verificar a ocorrência e distribuição de Cymbasoma longispinosum Bourne, 1890 em um estuário tropical amazônico da região norte do Brasil. As coletas foram realizadas bimestralmente de julho/2003 a julho/2004 em dois diferentes transectos (rios Muriá e Curuçá) situados ao longo do estuário do Curuçá (Pará, Norte do Brasil). Amostras foram coletadas durante marés de quadratura por intermédio de arrastos com redes de plâncton de 200μm de abertura de malha, através de um pequeno barco a motor (1 a 1,5 knots). Amostras adicionais de água subsuperficial foram coletadas para determinação dos parâmetros ambientais. Machos e fêmeas de C. longispinosum foram observados apenas durante os meses de setembro e novembro/2003. O maior número de organismos foi encontrado em setembro/2003, no transecto do rio Muriá. A presença de C. longispinosum nas amostras obtidas durante setembro e novembro/2003 poderia estar provavelmente relacionada ao período reprodutivo desta espécie no estuário estudado, o qual está diretamente relacionado ao período seco na região. Os mais elevados valores de salinidade, bem como os elevados números de indivíduos observados no mês de setembro/2003 confirmam a suposição anterior, visto que nenhum indivíduo de C. longispinosum foi registrado durante os meses que incluem o período chuvoso (janeiro a junho)

In this study nodulated cowpea plants were exposed to a progressive drought-stress followed by rewatering in order to establish mechanisms related to the nodule sensitivity to N 2 fixation. Water stress caused a prominent decrease in the dry matter of leaf and nodule in contrast to the root growth that was stimulated. The drought-stressed plants showed a great decline in the ureide concentration of xylem sap whilst the concentration of the nodule leghaemoglobin decreased slightly. The stressed-nodules had significant accumulation of soluble carbohydrates in parallel to intense increase in the concentration of ureide, total amino acid and proline. After two days rewatering, the leaf growth showed a significant enhancement whereas in nodules a poor recovery was observed. In addition, the nodule N 2 fixation capacity did not improve after rehydration whereas the sap ureide experienced only a slight recovery and surprisingly the content of nodule soluble protein continued to drop. In contrast, a significant recovery in the nodule leghaemoglobin content was observed. Rewatering greatly induced depletion of both sucrose and total soluble sugar contents of nodules that were associated to a great decrease in the concentration of ureide, proline and amino acids, especially in leaves. Conversely the poor recovery of cowpea nodules after rehydration was apparently related to a carbohydrate shortage.Key words: leghaemoglobin, ureide, symbiose, water stress, Vigna unguiculata. Resumen Acumulación de componentes nitrogenados y reducción de carbohidratos en la fijación de nitrógeno de plantas de Vigna unguiculata (L.) Walp sometidas a estrés hídrico y rehidratadasA fin de establecer los mecanismos relacionados con la capacidad de los nódulos para fijar nitrógeno atmosférico, se expusieron plantas de Vigna unguiculata (L.) Walp noduladas a un estrés progresivo de sequía seguido de rehidratación. La sequía produjo una importante disminución en la materia seca de las hojas y de los nódulos, y en cambio estimuló el crecimiento de las raíces; por otro lado, hubo una gran disminución en la concentración de ureidos de la savia del xilema. Los nódulos sometidos a estrés presentaron una acumulación significativa de carbohidratos solubles, junto con un intenso aumento de la concentración de ureidos, aminoácidos totales y prolina, disminuyendo levemente la concentración de leghemoglobina. Tras dos días de rehidratación, el crecimiento de las hojas aumentó significativamente, pero tanto los ureidos de la savia como los nódulos sólo se recuperaron de forma leve, y no aumentó su capacidad de fijación de N 2 . Además, sorprendentemente, el contenido de proteínas solubles de los nódulos siguió disminuyendo, aunque el contenido de leghemoglobina se recuperó significativamente. Una rehidratación intensa indujo reducción tanto en el contenido de sacarosa como de azúcares solubles totales de los nódulos, junto con una gran disminución en la concentración de ureidos, prolina y aminoácidos, especialmente en las hojas. La pobre recuperación ...