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Treatment of 10 days old maize seedlings with metribuzin and pretilachlor near the recommended fielddose resulted in differential reductions in shoot fresh and dry weights during the following 16 days. Metribuzin showed great and consistent reductions, however, the reduction induced by pretilachlor, mostly nullified by the end of the experiment. Moreover, there were differential accumulations of lipid peroxides, carbonyl groups and H2O2 in maize leaves; metribuzin caused the greatest accumulation. Meanwhile, levels of thiol forms and reduced glutathione (GSH) were much more induced by pretilachlor than metribuzin; the contrary was true regarding oxidized glutathione (GSSG). The ratio of GSH/ GSSG was highest following pretilachlor treatment and least by metribuzin. On the other hand, activities of glutathione-S-transferases (GSTs, EC 2.5.1.18), c-glutamyl- cysteine synthetase (c-GCS, EC 6.3.2.2), glutathione synthetase (GS, EC 6.3.2.3), glutathione peroxidase (GPX, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) were more enhanced in maize leaves by pretilachlor than metribuzin. These findings suggest the occurrence of an oxidative stress differentially induced in maize by the herbicides, a state that was most pronounced with metribuzin. Pretilachlor was concluded to be the least phytotoxic to maize, while metribuzin was the most, this differential tolerance seemed to be related to the induction of GSH and GSH-associated enzymes.
Nine-day-old seedlings of two wheat cultivars (Misr1 and Sakha93) were treated with NaCl at 75, 150 and 225 mM for 15 days with or without the presence of 10 mM CaCl₂. All concentrations of NaCl led to significant decreases in fresh and dry weights of only Sakha93; however, Misr1 seemed to be affected only at the highest concentration. Nonetheless, growth parameters of both cultivars under normal conditions were most likely similar. On the other hand, lipid peroxides (as MDA) and H₂O₂ were greatly accumulated particularly in Sakha93; significant increases were detected in Misr1 treated only at 225 mM. Also, all concentrations of NaCl decreased GSH content in Sakha93; nevertheless, there were no great differences among both cultivars under normal conditions. On the other hand, the activities of the enzymatic antioxidants, GR, GST, CAT and POD were unaffected in Misr1 by all concentrations but inhibited in Sakha93. AOX responded differently to NaCl, there were decreases in Misr1 by 75 and 225 mM and in Sakha93 by 75 and 150 mM. However, the application of CaCl₂ alleviated the impacts of NaCl; there was a retraction in growth reduction in Misr1 to reach most likely those of the control. In addition, the accumulated MDA and H₂O₂ were greatly counterbalanced. On the contrary, the decreased GSH contents seemed unrecovered in Sakha93 in spite of the alleviations in magnitudes. Moreover, there were recoveries in the activities of GR and POD in Sakha93; nevertheless, GST and CAT activities remained significantly inhibited. These findings suggest that Misr1 is a more tolerant cultivar to NaCl than Sakha93. Moreover, the results reveal that ROS scavenging is efficient and became more inducible in the less susceptible than in the more susceptible cultivar. The response of AOX appeared to coincide with antioxidants so that the damage which was inflicted by NaCl can be ameliorated by overexpression of antioxidants especially with the presence of CaCl₂.
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