The natural environment of plants is composed of a complex set of abiotic stresses and their ability to respond to these stresses is highly flexible and finely balanced through the interaction between signaling molecules. In this review, we highlight the integrated action between reactive oxygen species (ROS) and reactive nitrogen species (RNS), particularly nitric oxide (NO), involved in the acclimation to different abiotic stresses. Under stressful conditions, the biosynthesis transport and the metabolism of ROS and NO influence plant response mechanisms. The enzymes involved in ROS and NO synthesis and scavenging can be found in different cells compartments and their temporal and spatial locations are determinant for signaling mechanisms. Both ROS and NO are involved in long distances signaling (ROS wave and GSNO transport), promoting an acquired systemic acclimation to abiotic stresses. The mechanisms of abiotic stresses response triggered by ROS and NO involve some general steps, as the enhancement of antioxidant systems, but also stress-specific mechanisms, according to the stress type (drought, hypoxia, heavy metals, etc.), and demand the interaction with other signaling molecules, such as MAPK, plant hormones, and calcium. The transduction of ROS and NO bioactivity involves post-translational modifications of proteins, particularly S-glutathionylation for ROS, and S-nitrosylation for NO. These changes may alter the activity, stability, and interaction with other molecules or subcellular location of proteins, changing the entire cell dynamics and contributing to the maintenance of homeostasis. However, despite the recent advances about the roles of ROS and NO in signaling cascades, many challenges remain, and future studies focusing on the signaling of these molecules in planta are still necessary.

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Several plant species are traditionally used in Brazil to treat various inflammatory diseases. Tumor necrosis factor- (TNF-) α and chemokine (C-C motif) ligand 2 (CCL2) are key inflammatory mediators in diseases like rheumatoid arthritis and atherosclerosis, respectively; nevertheless, only a few extracts have been assayed against these targets. We herein report the effect of 19 plant extracts on TNF-α and CCL2 release by lipopolysaccharide- (LPS-) stimulated THP-1 cells, a human monocytic leukemia cell line, along with their radical scavenging activity on DPPH. The extracts of Caryocar brasiliense, Casearia sylvestris, Coccoloba cereifera, and Terminalia glabrescens inhibited TNF-α production in a concentration-dependent manner. Fractionation of these extracts potentiated the anti-TNF-α effect, which was shown to concentrate in polar fractions, mainly composed by polyphenols. Significant CCL2 inhibition was elicited by Lippia sidoides and Terminalia glabrescens extracts, whose fractionation resulted in highly active low polar fractions. All assayed extracts showed strong radical scavenging activity, but antioxidant activity did not correlate with inhibition of TNF-α or CCL2 production. Our results allowed identifying extracts with selective capacity to block cytokine production; therefore, further purification of these extracts may yield molecules that could be useful in the treatment of chronic inflammatory diseases.

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Effect of nitric oxide (NO) in mitigating stress induced by arsenic (As) was assessed in Pistia stratiotes, with NO supplied as sodium nitroprusside (SNP). Plants were exposed to four treatments: control, SNP (0.1 mg L(-1)), As (1.5 mg L(-1)), As + SNP (1.5 and 0.1 mg L(-1)), for seven days (analyses of growth, absorption of As and mineral nutrients) and for 24 h (analyses of concentration of reactive oxygen intermediates (ROIs), antioxidant capacity and photosynthesis). P. stratiotes accumulated high concentrations of As and this accumulation wasn't affected by the addition of SNP, but the tolerance index of the plant to As increased. SNP attenuated effects of As on the absorption of mineral nutrients (Ca, Fe, Mn, and Mg), but not for phosphorus, and maintained concentrations of ROIs to normal levels, probably due to the increase in antioxidant capacity. The As damaged the photosynthesis by the decrease in pigment contents and by disturbance the photochemical (loss of PSII efficiency and increases in non-photochemical quenching coefficient) and biochemical (reductions in carbon assimilation, increase in the C(i)/C(a) and phi(PSII)/phi(CO2) ratios) steps. The addition of SNP restored these parameters to normal levels. Thus, NO was able to increasing the resistance of P. stratiotes to As.

A alelopatia caracteriza-se pelos efeitos danosos ou benéficos que metabólitos secundários produzidos por plantas, microrganismos ou fungos liberados no ambiente exercem sobre o desenvolvimento de sistemas biológicos naturais ou implantados. O objetivo do trabalho foi avaliar o efeito alelopático de extratos aquosos de eucalipto (Eucalyptus globulus Labill.) e guaçatonga (Casearia sylvestris Sw.) na germinação e no crescimento inicial de mostarda (Brassica campestris L.), repolho (Brassica oleracea L. cv. capitata), brócolis (Brassica oleracea L. cv. italica), couve (Brassica pekinensis L.), alface (Lactuca sativa L. cv. grand rapids), tomate (Lycopersicum esculentum Miller), nabo (Brassica rapa L.), rúcula (Eruca sativa L.) e rabanete (Raphanus sativus L.). Foram testadas seis concentrações de cada extrato aquoso (10, 30, 50, 70, 90 e 100%) e comparadas com controle (água destilada), com cinco repetições cada, sendo distribuídas dez sementes das espécies cultivadas em cada repetição. Os extratos aquosos de E. globulus e C. sylvestris reduziram significativamente o percentual de germinação das sementes, o índice de velocidade de germinação, o crescimento inicial da parte aérea e do sistema radicular de todas as espécies cultivadas, com redução nestes parâmetros com aumento das concentrações utilizadas e, acarretando raízes mais espessas, atrofiadas e com maior número de pêlos absorventes. Assim, os resultados indicam a existência de potencial alelopático de E. globulus e C. sylvestris. Palavras-chave: Alelopatia, germinação, crescimento, Eucalyptus globules, Casearia sylvestris AbstractAllelopathy is characterized by the harmful or benefic effects caused by secondary metabolites, that are produced by plants, microorganisms or fungi and are released in the environment, on the development of natural biological systems or implemented ones. This study aimed to evaluate the allelopathic effects of aqueous extracts of eucalypt (Eucalyptus globulus Labill.) and wild coffee (Casearia sylvestris Sw.) on the germination and initial development of mustard (Brassica campestris L.), cabbage (Brassica oleracea L. cv. capitata), broccoli (Brassica oleracea L. cv. italica), kale (Brassica pekinensis L.), lettuce (Lactuca sativa L. cv. grand rapids), tomato (Lycopersicum esculentum Miller), turnip (Brassica rapa L.), rucola (Eruca sativa L.) and radish (Raphanus sativus L.). Six concentrations of each aqueous extract were tested (10, 30, 50, 70, 90 and 100%) and compared to control (distilled water), with five replicates of each concentration, being ten seeds of each crop distributed in each replicate. The aqueous extracts of E. globulus and C. sylvestris reduced significantly the percentage of seed germination, the index of