Neveen Talaat

Abstract Dual application [24-epibrassinolide (EBL) and spermine (Spm)] influence on the antioxidant machinery in water-stressed plants has received no attention. The present study, as a first investigation, was conducted with an aim to investigate the effects of EBL, Spm and their dual application on the \{ROS\} scavenging antioxidant defense machinery in plants subjected to drought conditions. This approach was assessed as possible mechanisms of drought tolerance and how these applications protect plants against oxidative stress. To achieve this goal, two maize hybrids (Giza 10 and Giza 129) were subjected to well-watered conditions and water-stressed conditions (75% and 50% of field capacity) with and without \{EBL\} and/or Spm foliar application. The grains were sown in plastic pots containing clay-loam (sand 37%, silt 28%, clay 35%) soil (Inceptisols; FAO), under greenhouse condition. Water deficiency significantly reduced growth, productivity, and membrane stability index, particularly in hybrid Giza 10. However, the follow-up treatment with the dual application (25 mg l?1 Spm + 0.1 mg l?1 EBL) detoxified the stress generated by drought and significantly improved the above parameters, particularly in hybrid Giza 129. Drought stress significantly increased \{H2O2\} and \{O2\} ? contents and caused oxidative stress to lipids assessed by the increase in \{MDA\} content. However, they were significantly decreased in stressed plants treated with the dual application. Moreover, dual application alleviated the detrimental effects of drought on the electrolyte leakage. Activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase and levels of ascorbate, glutathione, proline, and glycinebetaine were increased in response to drought treatments as well as foliar applications. Dual application significantly alleviated drought-induced inhibition in the activities of monodehydroascorbate reductase and dehydroascorbate reductase as well as in the ratios of AsA/DHA and GSH/GSSG. Overall, dual application improved the plant drought tolerance and decreased the accumulation of \{ROS\} by enhancing their scavenging through elevation of antioxidant enzymes activity and improving the redox state of ascorbate and glutathione.

No information is available regarding effective microorganisms (EM) influence on the enzymatic and non-enzymatic antioxidant defence system involved in the ascorbate-glutathione cycle under saline conditions. Therefore, as a first approach, this article focuses on the contribution of EM to the scavenging capacity of the ascorbate-glutathione cycle in salt-stressed plants. It investigates some mechanisms underlying alleviation of salt toxicity by EM application. Phaseolus vulgaris cv. Nebraska plants were grown under non-saline or saline conditions (2.5 and 5.0 dSm(-1)) with and without EM application. Lipid peroxidation and H2O2 content were significantly increased in response to salinity, while they decreased with EM application in both stressed and non-stressed plants. Activities of ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) increased under saline conditions; these increases were more significant in salt-stressed plants treated by EM. Activities of monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) and dehydroascorbate reductase (DHAR; EC 1.8.5.1) decreased in response to salinity; however, they were significantly increased in stressed plants treated with EM. Ascorbate and glutathione contents were increased with the increasing salt concentration; moreover they further increased in stressed plants treated with EM. Ratios of AsA/DHA and GSH/GSSG decreased under saline conditions, whereas they were significantly increased with EM treatment in the presence or in the absence of soil salinization. The EM treatment detoxified the stress generated by salinity and significantly improved plant growth and productivity. Enhancing the H2O2-scavenging capacity of the ascorbate-glutathione cycle in EM-treated plants may be an efficient mechanism to attenuate the activation of plant defences.

No information is available concerning the influence of dual application of 24-epibrassinolide (EBL) and spermine (Spm) on the nitrogen metabolism in plants subjected to drought conditions. As a first report, this investigation assesses the role of EBL, Spm, and their dual application on polyamine and protein pools in water-stressed plants. It explores the ameliorative effects of these foliar applications under water deficiency. Two maize hybrids (Giza 10 and Giza 129) were treated with or without EBL and/or Spm foliar applications under well-irrigated and drought-stressed conditions (75 and 50 {%} of field capacity). Dual application (25 mg l−1 Spm + 0.1 mg l−1 EBL) significantly relieved the drought-induced inhibition on the activities of ribulose-1,5-bisphosphate carboxylase and nitrate reductase and the contents of relative water, nitrate, and protein, particularly in hybrid Giza 129. Changes in the content of free polyamines and in the activity of polyamine biosynthetic and catabolic enzymes were detected when water-stressed plants were treated with EBL and/or Spm. Putrescine content and arginine decarboxylase activity were significantly increased in stressed hybrid Giza 10 plants treated by the dual application. However, spermidine and Spm levels as well as ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were significantly increased in stressed hybrid Giza 129 plants treated with the dual application. Diamine oxidase, polyamine oxidase, protease activity, carbonyl content, and ethylene formation were increased in response to water stress and significantly decreased when stressed plants were treated by the dual application. Total free amino acids, phenols, and flavonoids concentration were increased with the increasing water stress level; moreover, they further increased in stressed plants treated with the dual application. Overall, the combined utilization of EBL and Spm serves as complementary tools to confer plant drought tolerance by altering polyamine, ethylene, and protein levels.

Abstract No information is available regarding the influence of effective microorganisms (EM) on protein synthesis and polyamine balance in plants grown under saline conditions. Thus, as a first approach, this study sheds light on some different mechanisms that may protect EM-treated plants against salt excess. The response of common bean (Phaseolus vulgaris L.) cv. Nebraska to soil salinization [0.1 dS m?1 (non-saline), 2.5 and 5.0 dS m?1] and/or \{EM\} application was investigated. Plants grown in saline soils exhibited a significant decline in productivity, membrane stability index, nitrate reductase activity, nitrate and protein content, K+ concentration, and K+/Na+ ratio. However, \{EM\} application ameliorated the deleterious effects of salinity and significantly improved the above parameters. Soil salinity induced oxidative damage through increased lipid peroxidation and hydrogen peroxide content. \{EM\} application significantly reduced the oxidative damage. Polyamines responded to salinity stress by increasing its content, particularly putrescine level. The \{EM\} treatment changed the polyamine balance under saline conditions, a high increase in spermidine and spermine levels was observed. Moreover, \{EM\} application significantly reduced the activities of diamine oxidase and polyamine oxidase in salt-stressed plants. Both the modulation of polyamine pool and the regulation of protein synthesis can be one of the most important mechanisms used by EM-treated plants to improve plant adaptation to saline soils.

Abstract Little information is available concerning arbuscular mycorrhizal fungi (AMF) influence on carbon and nitrogen metabolisms in wheat under saline conditions. Thus, this study will shed light on some different mechanisms that play a role in the protection of wheat plants colonized by \{AMF\} against hyperosmotic salinity. Two wheat (Triticum aestivum L.) cultivars, Sids 1 and Giza 168, were grown under non-saline or saline conditions (4.7 and 9.4 dS m−1) with and without \{AMF\} inoculation. Root colonization was adversely affected by increasing salinity level, particularly in Giza 168. Soil salinity decreased plant productivity, membrane stability index, photochemical reactions of photosynthesis, the concentrations of N, K+, nitrate, chlorophyll, carbohydrates, and protein, the relative water content, and the activities of nitrate reductase and carbonic anhydrase. The reduction was more pronounced in Giza 168. Mycorrhizal symbiosis protected wheat against the detrimental effect of salinity and significantly improved the above parameters, especially in Sids 1. Under saline conditions, wheat plants colonized by \{AMF\} had higher gas exchange capacity (increased net \{CO2\} assimilation rate and stomatal conductance, and decreased intercellular \{CO2\} concentration), compared with non-mycorrhizal ones. Concentrations of soluble sugars, free amino acids, proline and glycinebetaine increased under saline conditions; these increases were more marked in salt-stressed plants colonized by AMF, especially in Sids 1. Soil salinization induced oxidative damage through increased lipid peroxidation and hydrogen peroxide levels, particularly in Giza 168. Mycorrhizal colonization altered plant physiology and significantly reduced the oxidative damage in plants exposed to salinity. Enhanced metabolism of carbon and nitrogen can be one of the most important mechanisms of plant adaptation to saline soils that are activated by AMF. This is the first report dealing with mycorrhization effect on the activity of carbonic anhydrase under saline conditions.

Two wheat (Triticum aestivum L.) cultivars, Sids 1 and Giza 168, were grown under non-saline or saline conditions (4.7 and 9.4 dS m-1) and were sprayed with 0.00, 0.05 and 0.10 mg l-1 24-epibrassinolide (EBL). Salt stress markedly decreased plant productivity and N, P, and K uptake, particularly in Giza 168. A follow-up treatment with 0.1 mg l-1 EBL detoxified the stress generated by salinity and considerably improved the above parameters, especially in Sids 1. Organic solutes (soluble sugars, free amino acids, proline and glycinebetaine), antioxidative enzymes (superoxide dismutase, peroxidase, catalase and glutathione reductase), antioxidant molecules (glutathione and ascorbate) and Ca and Mg levels were increased under saline condition, and these increases proved to be more significant in salt-stressed plants sprayed with EBL, par- ticularly at 0.1 mg l-1 EBL with Sids 1. Sodium concen- tration, lipid peroxidation, hydrogen peroxide content and electrolyte leakage were increased under salt stress and significantly decreased when 0.1 mg l-1 EBL was sprayed. Clearly, EBL alleviates salt-induced inhibition of pro- ductivity by altering the physiological and biochemical properties of the plant.