The study was carried out to determine the antimicrobial activities of Carica papaya and its major antimicrobial constituents (phytochemicals). The aqueous and ethanol extracts from the leaves and stem back of these plants were tested using well Diffusion method for their antimicrobial activity against some members of Enterobacteriales family isolated from diarrheic stool sample (Escherichia coli, Shigella spp, Salmonella typhi and Pseudomonas aeruginosa). Statistical analysis of the result shows that both the extracts demonstrated higher activities against bacteria tested, with the average zone of inhibition of 15.44mm, 14.78mm, 12.92mm and 11.31mm for Shigella, Escherichia coli, Salmonella typhi and Pseudomonas aeruginosa respectively. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of the extracts ranges between 12.5-100 mg/ml. Preliminary phytochemical analyses showed that the extracts contain alkaloids, tannins, terpenoids, anthraquinones, reducing sugar, amino acid, flavonoids, saponins, glycosides and phenols. Demonstration of antibacterial activity against the test isolates is an indication that there is possibility of sourcing alternative antibiotic substances in these plants for the production of newer antibacterial agents.

Light effects including its intensity, wavelength, and duration are important environmental factors that affects flavonoid accumulation. Ultraviolet (UV) light can induce flavonoid biosynthesis. Under normal condition, flavonoids are produced in response to stress, and they function as UV filters. In this paper, we review how light quality and quantity affect the accumulation of flavonoid in plant species. High light intensity can influence flavonoid accumulation, but in heliophytes, the opposite is true. Some medicinal plants require shady environment for flavonoid accumulation. In monocots, the flavonoid is situated in both epidermis and mesophyll while in dicot, it is found only in the epidermis. This review leads to a conclusion that high variation in flavonoids accumulation in response to light can occur within and between plant species.

Light is an important environmental factor that have an influence on a plants photosynthesis and production of secondary metabolites like phenolic compounds and flavonoid. Mangifera indica from the family Anacardiaceae is known to have bioactivity due to its phenolic and flavonoid contents. The objective of the study is to determine the influence of light on the photosynthesis and phenolic contents of M. indica. Photosynthesis of the plant was measured using a portable photosynthesis system referred to as LICOR-6400. Photosynthetic pigments as well as phenolic and flavonoid contents were quantified using a UV-VIS spectrophotometer. The outcome derived from the study shows that sun exposed leaves of the studied plant were having the maximum photosynthesis, saturation and compensation points (P < 0.05). Moreover, sun exposed leaves were having higher carotenoid, phenolic and flavonoid contents but lower chlorophyll contents. This leads to a conclusion that sun leaves of M. indica contribute the highest photosynthesis and phenolic contents to the plant.

Flavonoid and phenolics are secondary metabolites produced by plants in response to harsh environmental conditions. Light is one of the most important factor that affects their production. Mikania micrantha and Tridax procumbens are plants belonging to Asteraceae family, and they have bioactivity due to their flavonoid and phenolic contents. The objective of the research is to determine the effect of varying light intensities on the total flavonoid and total phenolic contents of M. micrantha and T. procumbens using three solvents (ethanol, methanol and water). Total flavonoid contents was determined based on the aluminium chloride colorimetry method while total phenolic contents was determined based on the folinchiocalteau reagent. The results obtained in the study shows that ethanol recovers more flavonoid and phenolic than the other solvents (P < 0.05). Besides, T. procumbens had more flavonoid and phenolic content compared to M. micrantha (P < 0.05). Nevertheless, the flavonoid and phenolic contents recovered from sun exposed plants was more than that recovered from shaded plants (P < 0.05). This leads to a conclusion that high light intensity can increase the concentration of flavonoid and phenolic of M. micrantha and T. procumbens.

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