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The recommended field dose (RFD) of isoproturon induced significant accumulations of H₂O₂ in the leaves of 10-d-old maize seedlings throughout the following 20 d; the accumulation increased with time and also with herbicide dose. Meanwhile, low doses significantly increased ascorbic acid, glutathione and thiols while high doses caused diminutions. Superoxide dismutase (SOD; EC 1.15.1.1) activity was significantly enhanced up to the 12th d whereas ascorbate peroxidase (APX; EC 1.11.1.7) activity was significantly reduced after the fourth d onwards. Catalase (CAT; EC 1.11.1.6) and guaiacol peroxidase (GPX; EC 1.11.1.7) activities were similarly increased during the first 4 d but decreased from the 12th and the eighth d, respectively. Low doses increased SOD and GPX activities but high doses led to diminutions whereas CAT and APX were reduced by all doses. The activities of γ-glutamyl-cysteine synthethase (γ-GCS; EC 6.3.2.2) and glutathione synthethase (GSS; EC 6.3.2.3) were enhanced for 4 d; high doses caused general reductions. Isoproturon significantly reduced activities of glutathione S-transferase (GST; EC 2.5.1.18) isoforms [GST(CDNB), GST(ALA), or GST(MET)] after the fourth d, however, it had no effect on GST(ATR). Similar reductions in activities of glutathione peroxidase (GSPX; EC 1.15.1.1) and glutathione reductase (GR; EC 1.6.4.2) were detected up to the 16th and the 12th d, respectively. The activities of GST isoforms, GSPX and GR were reduced by high doses. These changes seemed to be related and might point to an oxidative stress state that exacerbated with prolonged time and/or increased isoproturon dose.
Treatments of broad bean and maize seedlings with fluometuron, atrazine or rimsulfuron affected some parameters of oxidative stress. Fluometuron significantly reduced activity of Hill reaction (PSII), chlorophyll a+b contents and activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in leaves of both species and significantly increased contents of H2O2, lipid peroxides and carbonyl groups during the whole experiment. There were, moreover, significant inhibitions in activities of superoxide dismutase (SOD; E.C. 1.15.1.1), catalase (CAT; E.C. 1.11.1.6), ascorbate peroxidase (APX; E.C. 1.11.1.11) and guaiacol peroxidase (GPX; E.C. 1.11.1.7). Response to atrazine was, to some extent, similar to fluometuron throughout the entire experiment in broad bean and up mostly to the 12th day of the experiment in maize. The herbicide effect was more pronounced in broad bean than maize. These results point to indicate an occurrence of oxidative stress in both species by fluometuron and only in broad bean by atrazine. The increase in H2O2 content accompanied with drop in activities of SOD, CAT and peroxidases indicates a decline in its detoxification rather than increase in its synthesis. On the contrary, rimsulfuron seemed to have no effect on most of the tested parameters although there were transient significant increases in H2O2, lipid peroxides and carbonyl groups as well as activities of SOD, CAT, APX and GPX. These findings, based on the recovery in oxidative stress, indicate that fluometuron is involved in oxidative stress generation in both species but atrazine only in broad bean while rimsulfuron is not in both species.
Sunflower (Helianthus annuus L.) hybrid Hysun 333 (black seeded) was cultivated in a greenhouse and subjected during flowering stage to drought with or without the application of boron (B) and calcium (Ca) foliar sprays alone or in combination. The results revealed that drought induced a sharp decrease in seed fresh weight, seed protein and lipid contents. Application of B and Ca combined sprays overcame the drought effects on seed weight and seed lipid contents. Catalase expression was detected as a single band for all treatments where peroxidase isozymes were increased to seven, six of them were expressed when B sprays were applied with drought indicating that B has a major role in peroxidase up-regulation under drought conditions. SDS-PAGE analysis showed differential changes in protein profile with an appearance and/or disappearance of polypeptide protein bands, some of which were concluded to be drought-related proteins. The combined sprays of B and Ca seemed to overcome the effects of drought through minimizing band alterations (disappearance and/or appearance). The DD-RT PCR showed a variation in gene expression between the control and the other treatments. Sprays of B and Ca in combination seemed to be the most effective in band up-regulation and/or down-regulation that might play a possible role in improving tolerance of sunflower to overcome the drought deleterious effects.
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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