ABSTRACT(Allelopathic activity of Hovenia dulcis Th unb. (Rhamnaceae) leaves and pseudofruits on the germination of Lactuca sativa L. (Asteraceae)). Th is paper aims to evaluate the allelopathic eff ect of dry leaves and pseudofruits of Hovenia dulcis Th unb. on lettuce seeds. Th erefore, aqueous extracts of leaves and pseudofruits were prepared in 1%, 2% and 4% (m/v) concentrations. Four replicates were done of 25 lettuce seeds distributed in Petri dishes lined with Germitest paper and humidifi ed with the extracts, maintained in germination chamber at 25 °C, constant photoperiod and light presence for fi ve days, the control being distilled water. Th e percentage, speed, germination rate index, root length and aerial-part length of the seedlings were calculated, as well as the seeds eff ect in the presence of diff erent pH solutions. It was observed that the seedlings were signifi cantly aff ected in the presence of aqueous extracts of dry leaves and pseudofruits at 2% and 4% concentrations. Th e eff ects were not linked to pH and osmotic potential, indicating, therefore, allelopathic interference of Hovenia dulcis extracts.

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Sourgrass (Digitaria insularis L.) and fleabane (Conyza spp. L.) constitute a major challenge to weed management in soybean [Glycine max (L.) Merr.] production systems in Brazil, especially when both are resistant to glyphosate and present concurrently. The aim of this study was to evaluate the interaction of haloxyfop-P-methyl [methyl(R)-2{4-{3-chloro-5(trifluoromethyl)-2-pyridyloxy] phenoxy} propanoate] and 2,4-D [2,4-Dichlorophenoxyacetic acid-N-methylmethanamine] to control sourgrass at three to four tillers and flowering stages and 12-to 15-cm fleabane at vegetative stage. The experiments were arranged in a randomized complete block design with four replicates and were conducted twice. Treatments were composed of haloxyfop-P-methyl and 2,4-D applied sequentially at 3-, 6-, and 12-d intervals.Treatments also included an untreated check, haloxyfop-P-methyl, and 2,4-D sequentially (without interval) and stand-alone applications of both herbicides. All treatments across experiments completely controlled fleabane plants, except haloxyfop-P-methyl alone. Haloxyfop-P-methyl applied ≥6 d before 2,4-D controlled flowering and three-to four-tiller sourgrass plants at rates of 50 and 100%, respectively. Based on results of this study, haloxyfop-P-methyl should be applied ≥6 d before 2,4-D in a sequential application structure to control fleabane and sourgrass (three or four tillers) when present concurrently.

In this work, we compared nitrate-supplied plants (non-nodulated) with non-nitratesupplied plants (nodulated) under oxygen privation of root system (hypoxia) and re-oxygenation (post-hypoxia; recovery) in order to verify whether N sources affect the antioxidant system during oxidative stress caused by hypoxia and post-hypoxia conditions. Antioxidant enzymatic activities, ascorbate redox state, and reactive oxygen species (ROS) levels were analyzed in roots and leaves of two soybean genotypes, Fundacep 53 RR and BRS Macota at reproductive stage R2, during hypoxia and post-hypoxia in an experiment carried out in a hydroponic system. The antioxidant system was strongly induced in roots of nitrate-supplied plants of both genotypes, with high activity of superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and guayacol peroxidase. It also increased reduced ascorbate and ascorbate redox state and decreased ROS production under hypoxia and recovery, while in leaves of nodulated and non-nodulated plants, a slight increase on antioxidant system was observed. Nitrate may benefit soybean plants under hypoxic conditions and subsequent re-oxygenation by inducing the antioxidant system mainly in roots to cope with ROS production and reduce oxidative damage.

Waterlogging blocks the oxygen supply to the root system which inhibits respiration, and greatly reduces the energy status of cells that affect important metabolic processes. This study evaluated fermentative metabolism and carbohydrate contents in the root system of two soybean (Glycine max L. Merril) genotypes under hypoxic and post-hypoxic conditions. Nodulated plants (genotypes Fundacep 53 RR and BRS Macota) were grown in vermiculite and transferred to a hydroponic system at the reproductive stage. The root system was submitted to hypoxia by flowing N 2 (nitrogen) gas in a solution for 24 and 72 h. For recovery, plants returned to normoxia condition by transfer to vermiculite for 24 and 72 h. Fermentative enzyme activity, levels of anaerobic metabolites and carbohydrate content were all quantified in roots and nodules. The activity of alcohol dehydrogenase, pyruvate decarboxylase and lactate dehydrogenase enzymes, as well as the content of ethanol and lactate, increased with hypoxia in roots and nodules, and subsequently returned to pre-hypoxic levels in the recovery phase in both genotypes. Pyruvate content increased in nodules and decreased in roots. Sugar and sucrose levels increased in roots and decreased in nodules under hypoxia in both genotypes. Fundacep RR 53 was more responsive to the metabolic effects caused by hypoxia and post-hypoxia than BRS Macota, and it is likely that these characteristics contribute positively to improving adaptation to oxygen deficiency.Keywords: Glycine max, oxygen deficiency, enzyme activities, anaerobic metabolites, sugars IntroductionSoil waterlogging is a common abiotic stress worldwide in cultivated areas and influences the composition and productivity of soybean (Glycine max L. Merril) and most crops species (Jackson and Colmer, 2005;Githiri et al., 2006;Sairam et al., 2009;Kokubun, 2013). In waterlogged soils, gas exchanges between root systems and soil porous spaces are limited due to oxygen diffusion resistance that is around 10,000 times higher in water than in the air (Armstrong et al., 1994;Dongen et al., 2003;Zabalza et al., 2009;Bailey-Serres et al., 2012).Decrease in the oxygen level is the main factor that causes stress, leading to a chain signaling that unleashes a series of metabolic changes (Horchani et al., 2009), such as N metabolism and interconversion of amino acids (Puiatti and Sodek, 1999;Oliveira et al., 2013), changes in carbohydrates levels and energetic metabolism (Sousa and Sodek, 2002a), in an effort to secure plant survival and growth when exposed to hypoxic stress (Geigenberger, 2003). Anaerobic metabolism is activated under low oxygen concentration and as a consequence, there is a significant decrease in energy production that is derived mainly from glycolysis in contrast to oxidative phosphorylation (Kumutha et al., 2008;Horchani et al., 2009;Sairam et al., 2009;Zabalza et al., 2009). Plant survival under these conditions depends almost exclusively on anaerobic metabolism (Sousa and Sodek, 2002a).Due to the lack of O 2 as the fi...

Potencial alelopático de extratos aquosos de frutos de Solanum americanum Mill. sobre as sementes de rabanete RESUMO O objetivo deste trabalho foi investigar o potencial alelopático de extratos aquosos de frutos de erva-moura (Solanum americanum Mill.) sobre a germinação da semente e o crescimento inicial da plântula de rabanete (Raphanus sativus L.). Os extratos foram preparados nas concentrações 2; 4 e 8% e caracterizados quanto ao pH, potencial osmótico e perfil fitoquímico. Os testes foram constituídos de quatro repetições de 25 sementes de rabanete em placas de Petri contendo duas folhas de papel germitest e 5 mL de extrato aquoso. Para a germinação foram avaliados: a porcentagem de germinação (PG), a velocidade de germinação (VG), o índice de velocidade de germinação (IVG) e o coeficiente de uniformidade de germinação (CUG). Para o crescimento inicial foi avaliado: comprimento (radicular e da parte aérea), massa (fresca, seca e conteúdo de água) e teor de clorofila (a, b e total). Os extratos de frutos alteraram os parâmetros PG, VG e IVG para a germinação. Os extratos também causaram reduções no comprimento radicular, na massa fresca e nos teores de clorofila a. A ação dos extratos não está associada ao potencial osmótico e ao pH e os testes qualitativos de identificação revelam a presença de flavonóides, indicando, portanto, atividade alelopática. Palavras-chave:Alelopatia, germinação, crescimento inicial. Allelopathic potential of aqueous extracts of Solanum americanum Mill. fruits on radish seeds ABSTRACTThis study had the objective to test the allelopathic potential of aqueous extracts of nightshade fruits (Solanum americanum Mill.) on radish seed germination and leaflet early growth (Raphanus sativus L.). The extracts were prepared in the concentrations of 2, 4 and 8%, and characterized as to phytochemical profile, pH and osmotic potential. Treatments consisted of four replications of 25 radish seeds distributed in Petri dishes with two sheets of germitest paper and 5 mL of water extract. Germination parameters consisted of the germination percentage (PG), germination speed (VG), germination speed index (IVG) and germination uniformity coefficient (CUG). The initial growth was evaluated by length (root and shoot), mass (fresh, dried and water content) and chlorophyll content (a, b and total). The fruit extracts affected the PG, VG and IVG for germination. The extracts also reduced the root length, fresh mass and chlorophyll a levels. The extracts action is not related to the osmotic potential and pH and the qualitative identification tests reveals the presence of flavonoids, indicating allelopathic activity.

In this work, we evaluated the short time-induced oxidative stress-mediated rapid metabolic and physiological responses of resistant and susceptible Sumatran fleabane [Conyza sumatrensis (Retz.) E. Walker; syn.: Erigeron sumatrensis Retz.] to 2,4-D herbicide. Fixed conditions (25 °C and 65 ±5% relative humidity), we assayed injury symptoms, chlorophyll a fluorescence and antioxidative systems of both resistant and susceptible biotypes to 2,4-D (1005 g a.e. ha-1). Under 15°C vs 25°C temperatures and light and dark conditions, oxidative stress-mediated damage was assayed on plants that received 2,4-D herbicide applications. The injury symptoms observed in the 2,4-D resistant biotype were rapid necrosis in leaves within 30 min, with the re-establishment of normal growth within 1- to 2-weeks after 2,4-D treatment. The basal antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in the resistant biotype were greater than to the susceptible, though the activities of all enzymes generally did not differ between untreated and treated in the resistant biotype. The resistant biotype showed great reduction (at 1 and 4 h after application) in the photosynthetic electron transport chain performance index, while in the susceptible biotype these metabolic changes were detected only after 4 h. The resistant biotype recovered from the foliar damage 1- to 2-weeks after 2,4-D application, while the susceptible biotype was controlled. The production of H2O2 was responsive to temperature and increased faster in the 2,4-D-resistant biotype than in the susceptible one at both 15°C and 25°C; however, there was a greater increase at 25°C in the resistant biotype. The H2O2 production was not light-dependent in 2,4-D-resistant C. sumatrensis, with increases even under dark conditions. The 2,4-D resistant biotype showed rapid photosynthetic damage, possibly due to the rapid necrosis and leaf disruption, and increased the H2O2 content compared to the susceptible biotype.

Alelopatia se refere à capacidade que determinada planta tem de interferir no metabolismo de outra, por meio de compostos químicos liberados no meio. O objetivo deste trabalho foi determinar a influência alelopática de extratos aquosos de folhas de Phytolacca dioica L. na germinação e crescimento inicial de plantas de tomate e picão-preto. Extratos foram preparados nas concentrações 1%, 2%, 4% e 8%. Foram medidos o pH e o potencial osmótico dos extratos e realizada a análise fitoquímica das folhas. Nos experimentos foram utilizadas quatro repetições de 25 sementes distribuídas em placas de Petri com duas folhas de papel germitest umedecida com 5mL de extrato. Foi avaliada a porcentagem de germinação (PG), velocidade de germinação (VG), índice de velocidade de germinação (IVG), comprimento (raiz e parte aérea) e massa (fresca e seca) das plântulas de tomate e picão-preto. O pH e o potencial osmótico mantiveram-se dentro de padrões aceitáveis e a análise fitoquímica das folhas revelou a presença de flavonóides. A PG, VG e IVG foram afetados nos tratamentos mais concentrados (4 e 8%), o comprimento e a massa das plântulas de tomate e picão-preto foram afetados em todos os tratamentos. Tratamentos a 8% inibiram totalmente o processo germinativo das plantas.