Biocompatibility and ecotoxicity concerns associated with chemically produced metallic nanoparticles have led to an increasing interest in the development of environmentally benign alternatives for nanoparticle synthesis using biological platforms. Herein, we report the utilization of an extract of seed-derived callus of Catharanthus roseus for the production of stable silver nanoparticles (Ag NPs). The bioreduction of silver ions was evident from UV-Vis spectroscopy results: the absorption maxima were observed at 425 nm, indicative of elemental silver. Transmission electron micrographs revealed that the Ag NPs were well-dispersed and predominantly spherical with particle sizes in the range of 2-15 nm. The synthesized Ag NPs exhibited colloidal stability in an aqueous dispersion for a period of 120 days, as indicated by UV-Vis absorbance spectra and zeta potential measurements. Fourier transform infrared spectroscopy revealed the possible utilization of hydroxyl groups and amides in the reduction of silver ions and surface stabilization of the Ag NPs, respectively. Notably, the synthesized Ag NPs showed considerable antibacterial action against Escherichia coli even after 8 weeks of storage under ambient conditions. Thus, cell extracts of cultured callus of Catharanthus roseus could be explored as an ecofriendly platform for the synthesis of stable and functional nanoparticles.

Fungi associated with three cultivars of melon seeds were investigated. The mycoflora were found to be more on the unshelled than on the shelled seeds of all the three cultirars tested. A total of nine fungal genera were isolated and identified while two were unidentified. C. vulgaris was infected with all the nine genera including the two unidentified genera. Percentage incidence of infection was observed to be higher for the unshelled than with the shelled seeds for all the cultivars. The genus, Aspergillus was the most predominant, with A. niger topping the list followed by R. stolonifer and the least was A. flavus. In view of the harmful effects of aflatoxin production by Aspergillus spp caution must be exercised in the consumption of stored 'egusi' until an adequate control measure is in place.

The effects of some phytohormones [indole acetic acid (IAA), indole butyric acid (IBA), gibelleric acid (GA 3), and kinetin] on cell dry weight, cell number, cell size, protein and chlorophyll contents of Chlorella sorokiniana IAM-C212 were investigated under photoautotrophic conditions. Treatment with IAA (15 mg/l) and IBA (15 mg/l) resulted in significantly higher dry cell weight and cell number than the control (P < 0.05) but there were no significant effects of GA 3 and kinetin on cell growth as expressed by dry cell concentration (g/l) and cell population (cells/ml). Treatment with IAA at a concentration of 10 or 15 mg/l gave the highest cell dry concentration of 4.68 g/l after eight days of cultivation, which is more than 9 times higher than the value obtained in the control culture (without phytohormone). The optimum concentration of each of the phytohormones for C. sorokiniana cell enlargement was 20 mg/l. At this concentration, the average cell sizes were 81.07, 78.67, 78.07, 66.90 and 68.1 µm for GA 3 , kinetin, IAA, IBA and control, respectively. Addition of 15 mg/l of IAA or GA 3 to the culture resulted in significantly higher extractable chlorophyll contents than the control (P < 0.05) but the effects of IBA and kinetin were not significant (P > 0.05). The protein contents of the cells cultivated with 20 or 10 mg/l of GA 3 , 15 mg/l of kinetin, and 15 mg/l of IBA or IAA were 46.64, 45.83 and 45.81%, respectively. In the control experiment, the protein content was 43.38% after eight days of cultivation, showing that treatment with these phytohormones had no significant effect on the protein contents of the cells (P > 0.05). Combination of IBA and GA 3 exhibited synergistic effect on growth and productivity of C. sorokiniana but there was no synergistic effect when IAA was combined with either GA 3 or kinetin.

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