Welcome to the Google Science Fair 2011 site of my Project:
The Effect of Ultraviolet Light on Allelochemical Production, such as Phenolic Compounds, in Helianthus annuus Foliage Leachates and the Response of Ipomoea purpurea to these Leachates
By Shaun H Y
Helianthus annuus (Sunflower) is known to inhibit the growth of plants like Ipomoea purpurea (Tall Morning Glory) via allelochemicals produced in its leaves and other parts. Allelochemicals are secondary metabolites that affect growth and development of neighbouring organisms such as other plants, algae, bacteria or fungi, in response to various environmental stresses.


I investigated the effect of ultraviolet exposure of Helianthus annuus on water-soluble allelochemical production, such as phenolic compounds, in Helianthus annuus leaf leachates and their effect on the growth and physiology of Ipomoea purpurea seedlings.


I grew Helianthus annuus plants for 4 weeks and then irradiated them daily for 1 week with UV for 0, 3, 6, 9 and 12 hours while also providing them with a total of 12 hours of visible light from a florescent lamp. I then prepared 3% aqueous leaf leachates and determined their content of phenolic compounds using the Folin-Ciocalteu assay followed by spectrophotometric analysis at an absorbance of 750nm. After that, I treated Ipomoea purpurea seeds with these leachates for 1 week and monitored the percentages of its germination, respiration rates, dry mass, root physiology, and root and shoot lengths.


Results showed that the phenolic concentrations in Helianthus foliage leachates increased with longer UV exposure. I found that leachates from plants with longer exposure to UV inhibited germination, respiration rates, gain in dry mass and root and shoot extensions of Ipomoea purpurea seeds or seedlings to a greater extent. Roots of Ipomoea purpurea seedlings grown in leachates from plants with 12 hours of UV exposure had fewer root hairs and degenerate vascular bundles and pith tissue when compared with controls grown with 0 hours of UV exposure and 12 hours of visible light, suggesting that Helianthus-derived allelochemicals inhibit Ipomoea purpurea growth by interfering with nutrient or water uptake and nutrient storage in the latter.


Hence, increasing global UV levels may stimulate allelochemical production in Helianthus annuus and I believe that their leachates could be used as natural herbicides against plants susceptible to their allelopathic effects.
Here is a 20-slide presentation summarizing my project: 

GSF Presentation


Project Summary
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