Potential fungicidal and insecticidal proteins present in seeds Dioclea megacarpa Rolfe

• Main Author: Adelina Braga Batista
• Other Authors: Ilka Maria Vasconcelos
• Format: Others
• Language: Portuguese
• Published: Universidade Federal do Cearà 2009
• Subjects: Lectina; Saccharomyces cerevisiae; Calosobruchus maculatus; Lectin; BIOQUIMICA
• Online Access: http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=3789

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior === Dioclea megacarpa Rolfe is the correct synonym for D. relexa var. grandiflora. This species belongs to Fabaceae, the legume family. Previous studies, realized in our research group, showed the presence of active proteins for several phytopathogenic fungi in the seeds of this species, among of them Aspergillus niger. Thus, the present work was proposed with the objective of determining the bioactivity of protein(s) from D.megacarpa seeds against fungi, leading to its/their purification and partial characterization and further investigation of its/their action mechanism. Another approach of this work it was analyze the insecticidal potential of glucose/mannose-specific lectin, isolated from D.megacarpa seeds (Moreira et al., 1983), against the cowpea bruchid Callosobruchus maculatus. For this, seed flour was placed in contact with 0.15 M NaCl (1:5, w/w), followed by stirring for 3 h, filtration through a nylon cloth, re-extraction for 1 h, centrifugation at 11,500 x g, for 30 min, at 4 oC. The supernatant obtained, named total extract, showed antifungal activity against A. niger and presented several bioactive proteins, including lectin (129.27 UH/mgP, using trypsinized rabbit erythrocytes), trypsin inhibitor (18.91 mg de tripsina inibida/gF), urease (47.50 U/gF), toxin (LD50 119.60 mgP/Kg mice body weight ), chitinase (1.66 nKat/mgP) e β-1,3-glucanase (0.55 nKat/mgP). On the other hand, peroxidasic and proteolytic activities were not detected. For purification of antifungal principle, several chromatographies were performed on Sephadex G-50, Chitin and Resource Q, this last connected to an FPLC system. The purified antifungal protein, named Dm-PAF, with apparent molecular mass of 67-68 kDa (SDS-PAGE), did not show any haemagglutinating or chitinolytic activity and presented its NH2-terminal sequence blocked. Dm-PAF, at a very low concentration (0.015 ÂgP/ÂL), it was able to inhibit the growth of Saccharomyces cerevisiae and Candida tropicalis yeasts. The investigation of the antifungal action mechanism excluded the possibility of interaction between Dm-PAF and H+-ATPase pumps. In addition, the glucose/mannose-specific lectin, obtained from Sephadex G-50 column, exhibited a potent insecticidal activity against C. maculatus, interfering in important parameters related to life cycle of this insect. These data show to be the D. megacarpa seeds a rich source of biologically interesting proteins, possibly involved in the defense mechanism of plants === Dioclea megacarpa Rolfe à usada como sinonÃmia de D. relexa var. grandiflora, uma espÃcie pertencente à famÃlia Fabaceae (Leguminosae). Estudos prÃvios, realizados por nosso grupo de pesquisa, demonstraram a presenÃa em suas sementes de proteÃnas ativas contra fungos fitopatogÃnicos, dentre esses Aspergillus niger. Assim, o presente trabalho foi proposto no intuito de avaliar a bioatividade de proteÃnas de sementes de D. megacarpa contra fungos, conduzindo à sua purificaÃÃo e caracterizaÃÃo parcial, bem como à investigaÃÃo de seu mecanismo de aÃÃo. Outro objetivo deste trabalho foi examinar o potencial inseticida da lectina com especificidade por glucose-manose, isolada de sementes de D. megacarpa (Moreira et al., 1983), contra o bruquÃdeo do feijÃo-caupi Callosobruchus maculatus. Para tanto, farinha de sementes foi posta em contato com NaCl 0,15 M (1:5, p/v), seguida de agitaÃÃo contÃnua por 3 h, filtraÃÃo em pano de trama fina, re-extraÃÃo por 1 h e centrifugaÃÃo a 11.500 x g, 30 min, 4 oC. O sobrenadante obtido, denominado de extrato total, se mostrou ativo contra A. niger e apresentou vÃrias proteÃnas bioativas, compreendendo lectina (129,27 UH/mgP, com eritrÃcitos tripsinizados de coelho), inibidor de tripsina (18,91 mg de tripsina inibida/gF), urease (47,50 U/gF), toxina (DL50 119,60 mgP/Kg de peso corpÃreo de camundongo), quitinase (1,66 nKat/mgP) e β-1,3-glucanase (0,55 nKat/mgP). Por outro lado, atividades peroxidÃsica e proteolÃtica nÃo foram detectadas. Para purificaÃÃo da proteÃna antifÃngica, foram realizadas cromatografias em matrizes de Sephadex G-50, Quitina e Resource-Q, essa Ãltima acoplada ao sistema de FPLC. A proteÃna antifÃngica purificada de sementes de D. megacarpa, denominada de Dm-PAF, com massa molecular aparente de 67-68 kDa (PAGE-SDS), nÃo mostrou atividades hemaglutinante e quitinÃsica e apresentou sua seqÃÃncia NH2-terminal bloqueada. Dm-PAF, em concentraÃÃo baixÃssima (0,015 ÂgP/ÂL), se mostrou capaz de inibir o crescimento das leveduras Saccharomyces cerevisiae e Candida tropicalis, cuja investigaÃÃo do mecanismo de aÃÃo nÃo revelou envolvimento dessa proteÃna com bombas de H+-ATPase. Em adiÃÃo, a lectina ligante a glucose-manose, obtida na cromatografia em Sephadex G-50, mostrou potente atividade inseticida contra C. maculatus, interferindo em parÃmetros importantes relacionados ao ciclo de vida do inseto. Os dados apresentados mostram as sementes de D. megacarpa como uma rica fonte de proteÃnas interessantes, possivelmente envolvidas no mecanismo de defesa das plantas