1. Introduction Light is an essential element for plant growth and development. Light is made of a spectrum of wavelengths. Plants have developed unique photo absorption systems which can filter out different wavelengths. To date the effects of red, far red and blue light have been well documented. This has been successful due to the identification of photoreceptors which perceive each wavelength. Amongst the spectrum of photosynthetically active radiation, green light is used the least by plants for photosynthesis. There are no known green light photoreceptors in plants, but green light is known to have physiological effects on plants (1). Green light signals have been shown to reverse blue light-induced stomatal opening (2), stimulate early stem elongation (3) and inhibit plastid gene expression (4). Plant’s ability to respond to green light suggests the existence of a green light receptor(s). Identification of an easily scorable phenotypic response in germinating seedlings under green light is the first step towards finding a green light specific photoreceptor(s). Identification and characterizing of such a receptor(s) can potentially help in controlling plant growth and development. Characterization of such a receptor can also help in understanding physiological process in different plants growing in different regions of the world. Methods The experiment was carried out on seeds from Arabidopsis thaliana (‘Columbia’ ecotype) and Nicotiana tabacum cv. “Samsun”. Seeds were sterilized with ethanol and bleach, and then plated on a nutrient rich media for germination. The first set of trials were carried out on media with sucrose as a carbon source. The second set of trials were carried out on media in absence of any carbon source. The plates were wrapped in foil and placed in 4 o C for four days for stratification. After dark and cold treatment two plates of Arabidopsis seeds and two plates of tobacco seeds were placed vertically inside one of two LED-light boxes. One of the light boxes was set to emit only red and blue light, each at 15  mol m -2 s -1. The other light box was set to emit red, blue, and green light, each at 10  mol m -2 s -1. The light intensity were measured using a quantum sensor. The light boxes used were custom-built in the Dhingra lab. The plated seeds were kept in the light boxes for a week. The germinating seedlings were photographed everyday at the same time. Data was collected on germination rates and overall root area. Measurements were done using Image J. Results Supplemental green light exhibited some effect on root length. However, under these experimental conditions these differences were not statistically significant. The removal of a carbon source from the growth media seemed to enhance the phenotypic difference between the two seedling groups. However no effect was scorable within the same seedling group. Conclusion and Future Work  The hypothesis tests true as supplemental green light at the given fluence rates does not generate a scorable phenotype for the parameters tested in this study.  A difference in chlorophyll and anthocyanin content was observed in the seedling grown under different conditions. Future work could incorporate measurement of relative amounts of anthocyanin and chlorophyll.  Light and hormone are known to interact with each other during early seedling development. Similar experiments could be conducted in conjunction with presence of plant hormones such as GA, BAP, IAA. References 1.Lin. C., Ahmad. A., Gordon. D., Cashmore. A. S. (1995) Expression of Arabidopsis cryptochrome gene in transgenic tobacco results in hypersensitivity to blue, UV-A, and green light. PNAS 92(18): 8423-8427. 2.Frechilla.S., Talbott. L.D., Bogomolni. R.A., Zeiger. E. (2000) Reversal of Blue Light-Stimulated Stomatal Opening by Green Light. Plant Cell Physiology. 41(2):171-176. 3.Folta. K (2004) Green Light Stimulates Early Stem Elongation, Antagonizing Light-Mediated Growth Inhibition. Plant Physiology 135:1407-1416 4.Dhingra, A., Bies, D.H., Lehner, K.R., and Folta, K.M. (2006) Green light adjusts the plastid transcriptome during early photomorphogenic development. Plant Physiology, 142(3):1256-1266. Effect of Supplemental Green Light on Seedling Development Aaron White, Derick Jiwan, Jake Abel, Artemis Harper, Kenneth Webb and Amit Dhingra Department of Horticulture and Landscape Architecture, Washington State University, Pullman WA A:Seedlings grown on carbonless media under RBG B:Seedlings grown on carbon containing media under RBG Effect of different light spectra and carbon source on seed germination and plant morphology A: Arabidopsis germinating under RBG light B: Arabidopsis germinating under RB light Red Blue Red Blue Green 0 cm 1 1.5 AB Effect of RB and RBG Light Acknowledgements This study was supported by the CAHNRS Undergraduate Research and Creative Projects Fellowship, The Auvil fellowship and start-up funds to AD. Hypothesis Supplemental green light will have no effect on seed germination, hypocotyl length or root length. Results Effect of RB and RGB on root length One of the custom-built LED light boxes used in this study