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This study was aimed to synthesize zinc oxide nanoparticles from the aqueous peel extract of Aloe vera and assess their antimicrobial activity against pathogenic bacteria and fungi. The nanoparticles were characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and transmission electron microscopy (TEM). UV-Vis spectroscopic analysis confirmed the synthesis of zinc oxide nanoparticles. Fourier transform infrared spectroscopy (FTIR) depicted functional groups associated with the formation of zinc oxide nanoparticles, whereas XRD showed their crystalline nature. Scanning electron microscopy (SEM) showed that nanoparticles were rough in appearance with agglomeration. Transmission electron microscopy (TEM) confirmed the size of nanoparticles from 50 to 220 nm with hexagonal shape. The antimicrobial activity of zinc oxide nanoparticles was assessed against pathogenic bacteria, Staphylococcus epidermidis (MTCC-3382), S. epidermidis (MTCC-3382), Klebsiella pneumoniae (MTCC-3384), Escherichia coli (MTCC-41) and fungi, Aspergillus niger (MTCC-404) and Aspergillus oryzae (MTCC-3107). The results showed the effectiveness of zinc oxide nanoparticles against E. coli (MTCC-41) and A. niger (MTCC-404). However, in combination with antibiotic, there was a decrease in the antimicrobial activity against bacteria and fungi as compared to antibiotics. Hence, a molecular research is needed to check the effect of zinc oxide nanoparticles on antibiotics.

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During an investigation of the disease profi le of Withania somnifera, it was observed that leaf spot is the most prevalent disease. Repeated isolations from infected leaf tissues and pathogenicity tests showed the association of fungal pathogen identifi ed as Alternaria alternata (Fr.) Keissler. Scanning electron microscopy showed various histological changes in the leaf tissues of infected plants. A decrease in total content of reducing sugars (20%) and chlorophyll (26.5%) was observed in diseased leaves whereas an increase was noticed in proline (25%), free amino acids (3%) and proteins (74.3%). High performance thin layer chromatography (HPTLC) analysis of secondary metabolites viz. withanolides, withaferin-A and total alkaloids of the diseased leaves vis-à-vis control revealed reduction in withaferin-A and withanolides contents by 15.4% and 76.3% respectively, in contrast to an increase in total alkaloids by 49.3%, information hitherto unreported in W. somnifera.

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The antioxidant activity, phenolic contents and phytochemical profile of acetone, methanol, water and ethyl acetate extracts of the stem bark of B. monosperma were investigated. Extracts showed highest antioxidant activity at 100 μg ml −1 with application of different assays: 2 -2 diphenyl-2 picrylhydrazyl (DPPH) scavenging (83.5% and 78.1%), reducing power (1.85 and 1.78), deoxyribose degradation site-specific (65.5% and 61.5%) and non-site-specific (67.1% and 66.5%) and chelating power (63.4% and 58.9%) in decreasing and increasing polarity of acetone extracts, respectively. However, nitroblue tetrazolium (NBT) showed scavenging of O 2 • radicals by 56.4% and 53.1% in decreasing and increasing polarity methanol extracts, respectively. Similarly, electron paramagnetic resonance (EPR)/spin-trapping exhibited highest radical scavenging activity with acetone extracts (12.6 mg g −1 Trolox). The results pointed to the significant antioxidant activities in acetone and methanol extracts. In most cases, the extracts obtained through decreasing polarity showed higher antioxidant activity. The phenolic content exhibited a strong association (r 2 > 0.9) with antioxidant activity. These results suggest that bark of B. monosperma can be a potential source of natural antioxidants.