Differential Contribution of Malic Enzymes during Soybean and Castor Seeds Maturation.

Malic enzymes (ME) catalyze the decarboxylation of malate generating pyruvate, CO2 and NADH or NADPH. In some organisms it has been established that ME is involved in lipids biosynthesis supplying carbon skeletons and reducing power. In this work we studied the MEs of soybean and castor, metabolically different oilseeds. The comparison of enzymatic activities, transcript profiles and organic acid contents suggest different metabolic strategies operating in soybean embryo and castor endosperm in order to generate precursors for lipid biosynthesis. In castor, the malate accumulation pattern agrees with a central role of this metabolite in the provision of carbon to plastids, where the biosynthesis of fatty acids occurs. In this regard, the genome of castor possesses a single gene encoding a putative plastidic NADP-ME, whose expression level is high when lipid deposition is active. On the other hand, NAD-ME showed an important contribution to the maturation of soybean embryos, perhaps driving the carbon relocation from mitochondria to plastids to support the fatty acids synthesis in the last stages of seed filling. These findings provide new insights into intermediary metabolism in oilseeds and provide new biotechnological targets to improve oil yields.

Identification of a tyrosine phosphatase involved in the response to mechanical injury in leaves of Ricinus communis.

Plants defend themselves against biotic or abiotic stress by triggering intracellular signaling pathways that regulate gene expression and responses to the offending agent. Phosphorylation and dephosphorylation represent major mechanisms for the regulation of plant defense pathways. Therefore, MAP kinases and phosphatases have been the focus of many studies in this area. This study identified three phosphatase activities, namely RcPPase I, II and III. Wounding increased the activity levels of RcPPase III, while the activities of RcPPase I and II remained constant compared to the control. N-terminal partial amino acid sequence, biochemical characterization with use of specific substrates and inhibitors indicated that the RcPPase III belong to the family of tyrosine phosphatases (PTPs).

Methyl jasmonate promotes the transient reduction of the levels of 2-Cys peroxiredoxin in Ricinus communis plants.

Jasmonates are signaling molecules that play a key role in the regulation of metabolic processes, reproduction and defense against insects and pathogens. This study investigated the effects of methyl jasmonate on the protein pattern of Ricinus communis plants and the activity of guaiacol peroxidase, an antioxidant enzyme. Methyl jasmonate treatment caused a transient reduction in guaiacol peroxidase activity. A similar response was observed for the levels of 2-Cys peroxiredoxin protein. Moreover, the levels of the small and large chains of Rubisco were also reduced. The transient reduction of the levels and activity of antioxidant enzymes could account for the increase in the levels of H2O2, an important signaling molecule in plant defense.

The thermal stability of a castor bean seed acid phosphatase.

The effect of temperature on the activity and structural stability of an acid phosphatase (EC 3.1.3.2.) purified from castor bean (Ricinus communis L.) seeds have been examined. The enzyme showed high activity at 45 degrees C using p-nitrophenylphosphate (p-NPP) as substrate. The activation energy for the catalyzed reaction was 55.2 kJ mol(-1) and the enzyme maintained 50% of its activity even after 30 min at 55 degrees C. Thermal inactivation studies showed an influence of pH in the loss of enzymatic activity at 60 degrees C. A noticeable protective effect from thermal inactivation was observed when the enzyme was preincubated, at 60 degrees C, with the reaction products inorganic phosphate-P (10 mM) and p-nitrophenol-p-NP(10 mM). Denaturation studies showed a relatively high transition temperature (Tm) value of 75 degrees C and an influence of the combination of Pi (10 mM) and p-NP (10 mM) was observed on the conformational behaviour of the macromolecule.

Monitoring of urban traffic emissions using some physiological indicators in Ricinus communis L. plants.

Plants of Ricinus communis L. in the city of Porto Alegre, in southern Brazil, were exposed to urban traffic exhaust emissions for 5 months and compared with controls kept at a site essentially free of direct motor vehicle emissions. No symptomatic visible injuries were observed, but significant differences could be measured in growth, enzymatic activities of total peroxidase and nitrate reductase, chlorophyll content, leaf buffering capacity, and N contents in leaves. Additionally, these data were compared with results from fumigation experiments under controlled conditions. The study showed that some physiological parameters in R. communis L. plants could be used as an appropriate bioindicator system for urban traffic contamination, and therefore it is recommended that dose-response relationships should be developed.