65ª Reunião Anual da SBPC

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

Evaluation of total soluble proteins in Vigna unguiculata plants under inoculation and water deficit

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

INTRODUÇÃO:

Cowpea (Vigna unguiculata [L.]Walp.) is a legume with high protein content, a large capacity of atmospheric nitrogen fixation (N2) and low requirements to soil fertility. Cowpea presents important agronomical characteristics, such as rusticity and early maturity, besides is being considered a plant adapted to limited water conditions. Water deficit is an abiotic factor that affects agricultural production, influencing aspects related to plant development, such as rate of photosynthesis decreases, reduction in leaf area, and stomata closure. The biological nitrogen fixation is the capacity to divide the molecule of nitrogen (N2) and to combine hydrogen atoms (H+), forming ammonium (NH4+), by a distinct group of microorganisms, singly or under symbiosis. The inoculation using Bradyrhizobium can alleviate the negative consequences in Vigna unguiculata plants induced by water deficiency, but study revealed that water supply limits on symbiotic efficiency.

OBJETIVO DO TRABALHO:

The objective of this study was to evaluate total soluble proteins in Vigna unguiculata plants exposed to inoculation and water deficit.

MÉTODOS:

The study was carried out in Instituto de Ciências Agrárias (ICA) of the Universidade Federal Rural da Amazônia (UFRA), city of Belém, state of Pará, Brazil. The plants remained in greenhouse environment under natural sunlight conditions. The substrate used for the plant growth was composed by a mixture of sand and silic in the proportion of 2:1.The experimental design used was carried out at randomized entirely factorial scheme with 2 cultivars, 2 water regimes, and 2 inoculation treatments, with 6 replicates. 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). The disks were saturation on deionised water during 24 h, and the dry matter was measured after 48 h in oven with air forced circulation at 80°C.Determination of the total soluble proteins was carried out with 100 mg of powder, incubated with 5 mL of extraction buffer. Quantification of the total soluble proteins was carried out at 595 nm in accordance with Bradford (1976). Data were subjected to variance analysis and when significant differences were detected, Scott-Knott test at 5% level. All statistical procedures were carried out with the SAS software.

RESULTADOS E DISCUSSÃO:

The inoculation promoted attenuation of the negative effects induced by water deficit on leaf relative water content. The decrease of this variable can be explained by the reduction in water availability in substrate, because the water deficiency induces loss of turgor and consequent stomatal closure which will affect other physiological processes such as photosynthesis and transpiration. Water deficit caused a significant decrease in total soluble proteins in both cultivars, in both inoculated and non-inoculated plants, with a slightly greater decrease for sensitive plants. The increased in total soluble proteins induced by inoculation suggests that bacteria action resulted in increasing of nitrogen supply through a secondary route, that is regulated by the nitrogenase, because since there was no corresponding increased in activity of nitrate reductase after inoculation in this study. The decrease in protein levels promoted by the water deficit is associated with a decrease of the protein synthesis combined with an increase of proteolytic enzymes, responsible for breakdown of soluble proteins in plants.

CONCLUSÕES:

The inoculation with Bradyrhizobium spp. showed positive influence about the levels of total soluble proteins and leaf relative water content, when compared with non-inoculated plants, regardless of condition water deficit.

Palavras-chave: cowpea, biological fixation, drought.