Análise de crescimento e produtividade do pak choi cultivado sob diferentes doses de nitrogênio

O objetivo deste trabalho foi avaliar a influência de diferentes doses de nitrogênio no crescimento e produtividade do pak choi. O experimento foi conduzido, em cultivo protegido, de outubro a novembro de 2007, em Marechal Cândido Rondon, PR. O delineamento experimental foi de blocos casualizados, com cinco tratamentos (0, 60, 105, 150 e 195 kg ha-1 de N) e quatro repetições. O nitrogênio foi aplicado em três diferentes épocas (transplantio, 7 e 14 dias após o transplantio). Foram realizadas cinco coletas das plantas, semanalmente, avaliando-se a produção de massa da matéria seca e área foliar, para obtenção das taxas de crescimento absoluto e relativo, taxa assimilatória líquida, razão de área foliar e área foliar específica. Na colheita, foram avaliados altura da planta, diâmetro e matéria fresca da parte aérea e produtividade. Incrementos na adubação nitrogenada até a dose de 195 kg ha-1 proporcionam incrementos no crescimento e produtividade do pak choi

Biological effects of stannous chloride, a substance that can produce stimulation or depression of the central nervous system

It was demonstrated that tin, as stannous chloride (SnCl2), can facilitate the neuromuscular transmission by accelerating the transmitter release from the nerve terminals in the mouse. When this salt is injected into laboratory animals, it can produce stimulation or depression of the central nervous system. Because calcium (Ca2+) influx into the cytoplasm is indispensable to release the transmitter, it would be possible that SnCl2 increases the Ca2+ influx at the nerve terminals but not by blocking the K+ channels. SnCl2 is known to inhibit the immune response in rodents and to induce tumor generation in thyroid gland. There is no general agreement regarding its genotoxicity and it was discussed that the effects of this salt might depend on the physicochemical conditions and the route of its administration. SnCl2 has been used in many sectors of human interest, such as food industry and nuclear medicine. This salt is directly administered to human beings endovenously, when it is used as a reducing agent to prepare 99mTc-radiopharmaceuticals which are also used for cerebral studies. SnCl2 is capable to promote the generation of reactive oxygen species (ROS) that are responsible for the oxidative stress. Oxidative stress has been related with aging and other neurological diseases. So, it is relevant to evaluate other biological effects of SnCl2. We decided to study these effects using Escherichia coli mutant strains, deficient in DNA repair genes, and supercoiled plasmid DNA. We evaluated the influence of medicinal plants, metal chelating agents, and ROS scavengers against the SnCl2 deleterious effects. Our results show that SnCl2 produced lesions in vitro as well as in vivo. This inactivation may be due to the production of ROS. We observed that the genotoxic effect of SnCl2 was partly inhibited or disappeared, when the treatments were done in the presence of medicinal plants, metal chelating agents, and ROS scavengers. In conclusion, these findings suggest that the SnCl2 biological effects may be associated with the generation of ROS. Moreover, we can speculate that ROS could be associated with the detrimental effects in the brain due to exogenous or endogenous metals. © 2002 Elsevier Science Inc. All rights reserved