65ª Reunião Anual da SBPC

E. Ciências Agrárias - 1. Agronomia - 5. Agronomia

NITRATE REDUCTASE ACTIVITY IN TWO CONTRASTING Vigna unguiculata CULTIVARS SUBJECTED TO WATER DEFICIT AND INOCULATION

Maria Antonia Machado Barbosa - Universidade Federal Rural da Amazônia - UFRA Gélia Dinah Monteiro Viana - Universidade Federal Rural da Amazônia - UFRA José Ricardo Santos Barbosa - Universidade Federal Rural da Amazônia - UFRA Kelly Nayara Nascimento Coelho - Universidade Federal Rural da Amazônia - UFRA Marcele de Cássia Henriques dos Santos Moraes - Universidade Federal Rural da Amazônia - UFRA Allan Klynger da Silva Lobato - Prof. Msc/Orientador - Universidade Federal Rural da Amazônia - UFRA

INTRODUÇÃO:

Cowpea (Vigna unguiculata [L.] Walp.) is a leguminous with higher protein content, large capacity of fixation of the atmospheric nitrogen (N2) and few exigent in soil fertility (Alves et al, 2009). Water deficit is an abiotic factor that affects the agricultural production with greater frequency and intensity, influencing aspects related to plant development such as decrease in photosynthesis rate (Fontana et al, 1992). Cowpea plants are considered tolerant to water deficit, and important mechanisms were developed by this species to support inadequate situation linked to limited water supplement. Benefic effects linked to inoculation on growth parameters as leaf, stem and root are largely explored and well known (Ramos et al., 1999; Silveira et al., 2001), however interference of this symbiotic process on water relation is few explored.

OBJETIVO DO TRABALHO:

This study has aim to investigate the relative water content and nitrate reductase activity in plants Vigna unguiculata exposed to the combined action of water stress and inoculation.

MÉTODOS:

The study was carried out in Instituto de Ciências Agrárias (ICA) of the Universidade Federal Rural da Amazônia (UFRA), Belém city, Pará state, Brazil. The Vigna unguiculata (L.) Walp. seeds used in this study were of Pitiuba and Pérola cultivars, in which are tolerant and sensitive to water deficit, respectively. The substrate used for the plant growth was composed by a mix of sand and silica in the proportion of 2:1, respectively. The experimental design used was completely randomized with 2 cultivars (tolerant and sensitive) combined with 2 water regimes (water deficit and control), and 2 inoculation forms (inoculated and non-inoculated). Leaf relative water content was evaluated on leaf disks of 10 mm diameter from each plant; 40 disks were removed and the calculation was done using the formula proposed by Slavick (1979). Nitrate reductase enzyme (E. was extracted from 200 mg of leaf and root samples and incubated in 5 mL of extraction buffer for 30 minutes at 30ºC, and all the procedures were carried out in the dark. The data were submitted to variance analysis and when significant differences occurred was applied to the Scott-Knott test at 5% level of error probability. The statistical analyses were carried out with the SAS software.

RESULTADOS E DISCUSSÃO:

The inoculated plants had higher leaf relative water content, compared with same treatments in non-inoculated plants, in both well-watered and water deficit treatments. Drought tolerant plants had a lower reduction in leaf water content under water deficit, compared with drought sensitive cultivars. The decrease of this variable can be explained by the reduction in water availability in substrate (Lawlor and Cornic, 2002), because the water deficiency induces turgor loss and consequent stomatal closing, which will affect other physiological processes such as photosynthesis and transpiration (Nogueira et al., 1998). Water deficit reduced nitrate reductase activity in all treatments. The lower nitrate reductase activity in inoculated plants could be due to nitrogen being absorbed in the N2 form and transformed into NH4 in the symbiotic process mediated by nitrogen fixing bacteria (Gerahty, 1992; Taiz and Zeiger, 2004), using the nitrogenase enzyme (Burris, 1999).

CONCLUSÕES:

This investigation revealed that inoculation increased the relative water content in the leaf than in water deficit that control treatments. The water deficit produced a decline in the activity of nitrate reductase in all the treatments.

Palavras-chave: Bean, drought, inoculation.