Plackett-Burman screening of physico-chemical variables affecting Citrus peel-mediated synthesis of silver nanoparticles and their antimicrobial activity.

With the growing resistance of pathogenic microbes to traditional drugs, biogenic silver nanoparticles (SNPs) have recently drawn attention as potent antimicrobial agents. In the present study, SNPs synthesized with the aid of orange (Citrus sinensis) peel were engineered by screening variables affecting their properties via Plackett-Burman design. Among the variables screened (temperature, pH, shaking speed, incubation time, peel extract concentration, AgNO3 concentration and extract/AgNO3 volume ratio), pH was the only variable with significant effect on SNPs synthesis. Therefore, SNPs properties could be enhanced to possess highly regular shape with zeta size of 11.44 nm and zeta potential of - 23.7 mV. SNPs purified, capped and stabilized by cloud point extraction technique were then checked for their antimicrobial activity against Bacillus cereus, Listeria innocua, Listeria monocytogenes, Staphylococcus aureus, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhimurium and Candida albicans. The maximum antimicrobial activity of SNPs was recorded against E. coli, L. monocytogenes and C. albicans with clear zone diameter of 33.2, 31.8 and 31.7 mm, respectively. Based on minimum inhibition concentration and minimum bactericidal concentration of SNPs (300 mg/l) as well as their effect on respiratory chain dehydrogenases, cellular sugar leakage, protein leakage and lipid peroxidation of microbial cells, E. coli was the most affected. Scanning electron microscopy, protein banding and DNA fragmentation proved obvious ultrastructural and molecular alterations of E. coli treated with SNPs. Thus, biogenic SNPs with enhanced properties can be synthesized with the aid of Citrus peel; and such engineered nanoparticles can be used as potent antimicrobial drug against E. coli.

Effect of drought on yield of ten wheat cultivars linked with their flag leaf water status, fatty acid profile and shoot vigor at heading.

Flag leaf and shoot growth at heading stage as well as ultimate yield capacity of ten wheat cultivars were assessed in a pot experiment under normal and drought conditions. Drought was imposed by withholding 25% of field capacity from the 45- day old plants for 21 days followed by normal irrigation until maturity. Leaf succulence degree and stomatal opening area as well as shoot biomass, density and distribution decreased in all cultivars in response to drought but to different degrees. On contrary, leaf sclerophylly degree and water saturation deficit increased in all cultivars as a result of drought. At the same time, drought caused marked alterations in leaf transpiration rate, hair features, abscisic acid content, osmotic adjustment and fatty acid profile of the concerned cultivars; with ultimate variable capacity for yield. The drought- induced changes in the estimated traits were graphically represented in a single map then they were correlated with each other. The considered cultivars could be eventually clustered based on their drought response; with Sids cultivars being the most drought tolerant whereas Shandaweel 1 and Giza 168 being the most sensitive.

Drought-induced change in yield capacity of ten wheat cultivars in relation to their vegetative characteristics at heading stage.

Ten wheat (Triticum aestivum L.) cultivars were tested in a semi-field experiment for drought response in terms of their flag leaf vigor, whole shoot growth and ultimate yield capacity. At booting stage, 25% of field capacity was held for 3 weeks, then the plants were normally irrigated. Based on split plot analysis of the pooled data, the order in which the source of variation could affect the estimated traits was watering level, then cultivar and finally the combination of both. At p ≤ 0.05, significant positive linear correlation was recorded between the drought-induced change in grain total carbohydrate content and leaf total carbohydrate content, between biological yield and each of water use efficiency for biomass and evapotranspiration efficiency as well as between economic yield and each of leaf catalase activity, water use efficiency for grain and hundred kernel mass. On contrary, significant negative correlation was recorded between the drought-induced change in shoot evapotranspiration rate and each of leaf proline content and shoot water content. Based on the drought-induced change in the estimated vegetative and yield traits, cluster analysis could sequester the concerned cultivars into drought-tolerant, moderate and sensitive ones; with Sids 13 being the most drought-tolerant cultivar as well as Shandaweel 1 and Giza 168 as the most drought-sensitive ones.