Optimum activity of an extracellular pectin lyase produced by Penicillium griseoroseum in submerged culture was after 120 h using 0.1% (w/v) citrus pectin as substrate. Sucrose at 0.1% (w/v) stimulated enzyme production and citrus pectin gave the highest activity of enzyme per unit growth.

The denaturation of beta-trypsin induced by urea was investigated by fluorescence and circular dichroism. A transient denatured state was found at 2 M urea in both intrinsic fluorescence spectrum and bis-(8-anilino-1-naphtalene sulfonate) (bis-ANS) binding. In addition, the absence of tertiary contacts and presence of secondary structure for this state, are consistent with an intermediate equilibrium state having features of molten globule.

The genetic elimination of lipoxygenase isozymes (LOX) and the Kunitz trypsin inhibitor (KTI) from soybean seeds is a way to overcome the problems associated with the undesirable beany flavor of soybean products. Although the role of the lipoxygenases in higher plants has not yet been established conclusively, several studies have indicated the physiological relevance of the lipoxygenase pathway induction in plants under biotic and abiotic stress conditions. To elucidate the effect of seed lipoxygenase and KTI elimination on soybean defense against injury, a biochemical assessment of the lipoxygenase pathway in soybean leaves subjected to the attack of Anticarsia gemmatalis (Lepdoptera:Noctuidae) was carried out in a commercial cultivar and three lines derived from this cultivar, which differ on the presence and absence of LOX and the protease inhibitor KTI. The soybean plants responded to the attack of the insect via the LOX pathway, by increasing LOX activity and protease inhibition in their leaves. Since jasmonic acid seems to activate transcription of genes encoding for protease inhibitors, the soybean plant responded to the injury via the LOX pathway, preferentially producing jasmonate and protease inhibitors. There was no association between the lack of LOX and KTI from the seeds and the leaf defense against injury, indicating that the loss of the genes for both proteins from soybean seeds does not interfere with the plant ability to respond to the attack of A. gemmatalis via this pathway.

No abstract

RESUMONeste trabalho, avaliou-se a capacidade da planta de soja de uma cultivar comercial, IAC-100, e de um genótipo IAC-100 TN que apresenta ausência de lipoxigenases nas sementes de responderem ao ataque de mosca-branca (Bemisia argentifolii) pela via das Lipoxigenases. Foi realizada a caracterização cinética do pool de lipoxigenases. Os valores de K Mapp decresceram nas plantas atacadas, sugerindo uma alteração no pool de lipoxigenases foliares. Valores similares de K Mapp , entre os genótipos, indicam que a remoção de lipoxigenases de sementes não interferiram na expressão de lipoxigenases em folhas. Ocorreu aumento significativo na produção de inibidores de proteases. Com esses resultados, infere-se que a produção de inibidores de proteases está envolvida no mecanismo de defesa de soja ao ataque da mosca-branca.Termos para indexação: Soja, lipoxigenases, mosca branca, defesa de planta.ABSTRACT This work evaluated the capacity of the soybean plant, from a commercial cultivar IAC-100 and from a genotype IAC-100 TN, with absence of lipoxygenases in their seeds, to respond to the attack by whitefly (sucking insect) by lipoxygenases pathway. The kinetic characterization of the pool of lipoxygenases was determined. The K Mapp values decreased, suggesting a change in the pool of lipoxygenases in response to the attack by whitefly. The similar K Mapp values suggest that the removal of the lipoxygenases from the seeds does not change the expression of LOX in the leaves. There was a noticeable increase in protease inhibitors. These results suggest that the production of protease inhibitors are involved in the defense mechanism of soybean plant against whitefly injury. INTRODUÇÃOLipoxigenases (E.C. 1.13.11.12) catalisam a dioxigenação estereoespecífica de ácidos graxos poliinsturados contendo o sistema cis,cis-1,4-pentadieno com formação dos respectivos derivados hidroperóxidos, originando, assim, moléculas reativas com atividades fisiológicas pronunciadas (VICK e ZIMMERMAN, 1983).Duas principais vias para o metabolismo dos hidroperóxidos de ácidos graxos produzidos pelas lipoxigenases, chamadas de Via das Lipoxigenases, vêm sendo propostas para plantas superiores. Essa via envolve a ação de duas enzimas, ou seja, hidroperóxido liase e hidroperóxido ciclase. Após a ação da hidroperóxido liase, pode ocorrer a produção de aldeídos, os quais podem inibir o crescimento de fungos, insetos e protozoá-Rios (CROFT et al., 1993), podendo também agir como