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vol.32 issue318S-rDNA SEQUENCING, ENZYME PATTERNS AND MORPHOLOGICAL CHARACTERIZATION OF TRICHOPHYTON ISOLATESWATER STRESS RESPONSE ON THE ENZYMATIC ACTIVITY IN COWPEA NODULES author indexsubject indexarticles search
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Brazilian Journal of Microbiology

Print version ISSN 1517-8382On-line version ISSN 1678-4405

Abstract

SILVEIRA, Joaquim Albenísio Gomes da; COSTA, Roberto Cezar Lobo da  and  OLIVEIRA, José Tadeu Abreu. DROUGHT-INDUCED EFFECTS AND RECOVERY OF NITRATE ASSIMILATION AND NODULE ACTIVITY IN COWPEA PLANTS INOCULATED WITH BRADYRHIZOBIUM SPP. UNDER MODERATE NITRATE LEVEL. Braz. J. Microbiol. [online]. 2001, vol.32, n.3, pp.187-194. ISSN 1517-8382.  http://dx.doi.org/10.1590/S1517-83822001000300005.

This study was carried out to establish comparative effects of drought and recovery on the nitrate assimilation and nodule activity related to N2 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.

Keywords : glutamine synthetase; leghemoglobin; nitrate reductase; N2 fixation; water stress; Vigna unguiculata (L.) Walp.

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