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71.
Leaf senescence is often caused by water deficit and the chimeric gene PSA612-1PT is an auto-regulated gene delaying leaf senescence. Using in vitro leaf discs culture system, the changes of contents of chlorophylls, carotenoids, soluble protein and thiobarbituric acid reactive substance (TBARS) and antioxidant enzymes activities were investigated during leaf senescence of PSA612-1PT modified gerbera induced by osmotic stress compared with the control plant (wild type). Leaf discs were incubated in 20%, 40% (w/v) polyethylene glycol (PEG) 6 000 nutrient solution for 20 h under continuous light [ 130 μmol/(m^2·s)]. The results showed that the contents of chlorophylls, carotenoids and soluble protein were decreased by osmotic stress with the decrease being more pronounced at 40% PEG, but that, at the same PEG concentration the decrease in the transgenic plants was significantly lower than that in the control plant. The activities of superoxide dismutase (SOD), catalases (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and dehydroascorbate reductase (DHAR) were stimulated by PEG treatment. However, the increases were higher in PSA612-IPT transgenic plants than in the control plants, particularly at 40% PEG treatment. Lipid peroxidation (TBARS content) was increased by PEG treatment with the increase being much lower in transgenic plant than in the control plant. It could be concluded that the increases in the activities ofantioxidant enzymes including SOD, CAT, APX, GPX and DHAR were responsible for the delay of leaf senescence induced by osmotic stress. 相似文献
72.
莫之玮 《东方少年(阳光阅读)》2007,(6):56-57
<正>一草是农民保留到最后的一份遗产,草是牧民缩写在大地上的柔韧鞭影,草是沙漠尽头生命的第一见证,草是孤守野花的忠诚卫士,草是倒写在人们心中的"小"字。 相似文献
73.
目的:测定粉花月见草中总黄酮的含量。方法:以无水乙醇作为回流提取溶剂,在375nm处用紫外可见分光光度法测定粉花月见草中总黄酮的含量。结果:测得粉花月见草中总黄酮的含量为1.4435mg/g,精密度RSD=0.14%(n=5),回收率为90.87%~98.98%。结论:该方法操作简便、准确、可靠,可用于植物中总黄酮的含量测定。 相似文献
74.
The magnetorheological (MR) fluid damper-based semiactive control systems have received considerable attention for protecting structures against natural hazards such as strong earthquakes and high winds. In this paper, a novel modal controller using wavelet packet transform (WPT) is proposed for the vibration control of distributed structures. In the proposed control system, the WPT method is utilized to decompose the acceleration measurement and select the modes containing most of the WPT energy component as the dominant modes. Then, a modal controller is designed to control the dominant modes and the optimal active control force is solved. Finally, Clipped-optimal con- trol law is adopted to determine the voltage applied to each MR damper. A Kalman-filter observer, which estimates the full controlled modal states from local accelerometer feedbacks, is designed for rendering the controller to be more applicable to distributed structures with a large number of degrees of freedom. A numerical example of a stadium roof structure installed with MRF-04K damper is presented. The effectiveness of the controller is evaluated under both Tianjin and El Centro earthquake excitations. The superior performance and adaptability of the controller for versatile loading conditions are demonstrated through the comparison with traditional truncated modal controller. 相似文献
76.
77.
肖检蓉 《湖南第一师范学报》2011,11(6):87-89,134
我国大学生的信息素养现状距信息时代的能力要求还有较大差距。主要原因之一就是现有的信息素养教育模式不能很好地适应人才培养要求。众包作为一种全新的理念和运作模式,成为支持网络时代图书馆创新的有效途径。通过总结信息素养教育的主要教学形式,以新生入馆教育为例,对众包模式的组织与管理进行了实践探索。 相似文献
78.
79.
以盆栽的喜旱莲子草(Alternanthera philoxeroides)为实验材料,研究了南方菟丝子(Cuscuta australis R.Br.)寄生对喜旱莲子草叶片光合特性的影响。结果表明,南方菟丝子寄生致使喜旱莲子草叶片的净光合速率(Pn)、蒸腾速率(E)、气孔导度(Gs)、水分利用率(WUE)、气孔限制值(Ls)、Fm值、Fv/Fm值和相对叶绿素含量都呈现明显的下降,而胞间CO2浓度(Ci)和Fo值表现出相反的趋势。南方菟丝子的寄生减弱了喜旱莲子草的光合作用,而净光合速率的下降主要是由非气孔因素限制引起的。 相似文献
80.
在长篇小说创作凋零和缺失状况下,刘玉栋《年日如草》的出版,对于刘玉栋本人和整个70后作家群来说,都是一个很重要的突破。从"二十世中国文学史"的角度来看农民与城市的关系,农民如何融入城市、进入城市是一个现代化、城市化的中心问题。刘玉栋的《年日如草》塑造了一个适应现代城市生活的二代农民形象,一个带有某种狡黠而不失善良本性的、以法律取代人情意识的农民形象。这是以往文学史所没有的,具有突破性意义。 相似文献