Aim: This study was carried out to investigate the impact of light intensity on plant growth and n-hexane extracts of the leaves of Hyptis suaveolens. Materials and Methods: Plants were subjected to full sunlight (FS, 58753 lux), medium light intensity (MLI, 35880 lux) and low light intensity (LLI, 1250 lux) and were grown in loamy soil for 16 weeks. The parameters investigated include leaf area, shoot and root weight, number of leaves, Net Assimilation Rate (NAR), Leaf Area Ratio (LAR), Relative Growth Rate (RGR), type and amount of volatile components from n-hexane extract present in the leaves, using GC-MS. Results: There were mostly slight differences in the growth parameters but consistently the plants subjected to FS showed highest growth rate followed by those subjected to MLI. The dry weight roots of LLI plants, were significantly lower than the other treatments at p = 0.05 and these plants did not flower. Though there were only slight differences between the growth parameters of plants subjected to different light intensities, type and quantity of volatile compounds varied markedly. Volatile compounds like Ar-Abietatriene and 1-Phenanthrenemethanol were present under the three varying light intensities. Furthermore, LLI induced the highest concentration of 1-Phenanthrenemethanol than the other treatments, while FS induced the highest concentration of Ar-Abietatriene. Though full sunlight improved the growth of plants, the number of volatile compounds increased with decreasing light intensity from 7 to 12 compounds in the n-hexane extracts. Conclusion: This report shows that low light intensity increases the volatile compounds of Hyptis suaveolens markedly and this could enhance its antimicrobial activity.
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