Jasmonates are a class of plant hormones that mediate various aspects in gene and metabolic regulation, defense, stress responses, reproduction and, possibly, communication. Oxidative stress stimulates synthesis of antioxidant metabolites and enhances antioxidant enzyme activities that could protect plant tissues. The aim of this study was to verify the effects of methyl jasmonate (JAME) treatment on the reactive oxygen species (ROS) and on the activities of H2O2 scavenging enzymes, such as superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX EC; 1.11.1.1), and guaiacol peroxidase (GPX; EC 1.11.1.7) in Ricinus communis leaves. The activity of CAT and GPX was transient while SOD activity decreased and APX increased after treatment with JAME. In addition, JAME exposure induced ROS accumulation.

Com o objetivo de avaliar a resposta de defesa da mamona (Ricinus communis) contra predadores, analisaram-se as alterações nas atividades de fosfolipases A2 (PLA2) em extratos de folhas de plantas, submetidas à injúria mecânica após diferentes intervalos de tempo. Observou-se que os níveis dessa enzima aumentaram de forma significativa (cerca de duas vezes) 15 e 60 min após o ferimento. As atividades que foram induzidas foram sensíveis ao ácido aristolóquico (10 mM), um inibidor específico para PLA2. A enzima induzida após 15 min foi denominada Rc-PLA2 I e apresentou uma massa molecular aparente, determinada por SDS-PAGE, de 40 kDa. A proteína induzida após 60 min, RcPLA2 II, apresentou uma massa molecular de 14 kDa. A seqüência N-terminal parcial da Rc-PLAII mostrou homologia com PLA2 de arroz e olmo. As fosfolipases foram parcialmente purificadas por associação da cromatografia de filtração em gel, seguida por eluição das bandas que apresentaram atividade enzimática após separação por PAGE não desnaturante.

In order to investigate the defense response in castor bean (Ricinus communis) against predators, we analyzed the effect of mechanical wounding upon the phospholipase A2 (PLA2) activity of leaf extracts. Time course experiments revealed that the highest levels of increased PLA2 activity (ca. two fold) occurred 15 min and 60 min after injury. The induced activities demonstrated high sensitivity towards aristolochic acid (10 mM), a PLA2 inhibitor. Based on SDS-PAGE analysis, the PLA2 activity induced 15 min after wounding migrated with a molecular mass of 40 kDa and was denoted RcPLA2 I. The protein activity induced 60 min after wounding, RcPLA2 II, migrated with a molecular weight of 14 kDa. Furthermore its N-terminal sequence shared homology with PLA2 from elm and rice. The PLA2 enzymes were purified to near homogeneity by a combination of gel filtration and electro-elution of protein bands after native PAGE.