SOLUBLE PROTEIN CONCENTRATION BY BRADFORD REVEALS DIFFERENCES IN THE METABOLISM OF ORA-PRO-NOBIS PLANTS AT DIFFERENT NITROGEN LEVELS

Abstract

Ora-pro-nobis (Pereskia aculeata Mill.) is a protein-enriched food, widely used in rural communities, presenting increasing importance in the food and pharmaceutics industries. The aim of this study was to determine the protein concentration by the Bradford and Kjeldahl methods in plant leaves of ora-pro-nobis under different nitrogen fertilizer levels, comparing these methods. Leaves of ora-pro-nobis from plants fertilized with different nitrogen levels (0, 50, 100, 200, and 400 kg N/ha) were harvested at 423 days after planting (DAP). For the method of Bradford, the leaves were grounded in liquid nitrogen and macerated in 50 mM Tris-HCl, pH 7.0, the homogenate was centrifuged and the soluble proteins were determined in the supernatant. To evaluate the protein profile, samples of the different treatments were separated by 14% SDS-Tricine-PAGE. The traditional method of Kjeldahl was performed using the correction factor 6.25. For both methods, the results indicated that there were changes in the concentration and composition of proteins present for different availability of N in the soil. The total protein by Kjeldahl increased up to the level of 100 kg N/ha, and the soluble protein by Bradford increased in N levels between 50 and 200 kg/ha. By SDS-Tricine-PAGE, there was an increase in intensity of bands in line with the Bradford method results. These results suggest that the evaluation of the soluble protein by the Bradford method allows assessing differences in the metabolism of ora-pro-nobis plants, expressing biological information that was relevant to physiological and nutritional studies.