Lipoxygenases (linoleate: oxygen oxido-reductases, EC 1.13.11.12) are a class of enzymes that catalyze the addition of molecular oxygen to 1,4 - cis,cis - pentadiene motifs of unsaturated fatty acids to form hydroperoxide products. Plant lipoxygenases use linoleic (18:2) or linolenic (18:3) acids as substrates and are involved in important physiological process such as biosynthesis of regulatory molecules, growth and development, senescence, responses to wounding, vegetative storage protein and may directly mediate host resistance to insect, fungal and bacterial pathogens. When plant tissues are damaged, by pathogens or mecanically injured, a series of lipid degradation occurs, via lipoxygenase pathway, giving rise to hydroperoxydes. Among several products formed it can be found traumatin, jasmonic acid, volatile aldehydes and oxyacids. In this work we evaluated the capacity of the soybean plant to respond to the attack of stem canker fungi (Diaporthe phaseolorum (Cke. e Ell.) f. sp. meridionalis), through the lipoxygenase pathway. Leaves from resistant (FT-Cristalina RCH) and susceptible (FT-Cristalina) cultivars were used for kinetic evaluation of lipoxygenase and biochemical quantitation of products from the lipoxygenase pathway. Plants from both cultivars, infected with the pathogen or mecanically injured, showed values of lipoxygenase specific activity higher than the controls in differents pH and temperature values. The lipoxygenase pool of both cultivars showed kinetic of Michaelis-Menten within the range of substrate concentration assayed. There were an increase in protease inhibitors and of total aldehydes contents, which are products of the lipoxygenase pathway. The biochemical and kinetic parameters suggest a response of the soybean plant through the lipoxygenase pathway.
Glycine max; lipoxygenase; Diaporthe phaseolorum; aldehydes; protease inhibitors
