Brouwer, Marieke , Griffin-Nolan, Robert , Melcher, Peter .
Investigating the role of green light in photosynthesis in Coleus spp.
We measured the ability of green light to power photosynthesis in two varieties of Coleus spp. (Red Head and Henna) grown under high and low-light conditions (900 and 300 mmol m-2 s-1). These plants were able to sequester CO2 using only green light energy (lmax = 550 nm) and shade adapted plants required only 30 umol m-2 s-1 of green-light energy to reach their photosynthetic compensation points. However, even though the high-light adapted plants of both Coleus spp. varieties did sequester CO2 using green-light energy, these plants could not overcome their higher, sun-leaf respiration requirements and only shade-adapted leaves had positive quantum efficiencies when exposed to green light intensities of c.30 umol m-2 s-1and above. To determine how various qualities and quantities of light affected electron flow through the photosystems of isolated chloroplasts, we measured the rate of reduction of an artificial electron acceptor 2,6-Dichlorophenol-Indophenol (DPIP) and found that the t1/2 values of DPIP reduction were the same for chloroplasts exposed to either white, red, blue or green light energy measured at three light intensities of 10, 50 and 500 umol m-2 s-1. We also observed anatomical variations of anthocyanin accumulation within leaves exposed to the two light treatments. With respect to the location of the chlorophyll layer, we observed that the low-light exposed plants had leaves with only a prominent abaxial anthocyanin layer and sun adapted plants had leaves with both an intense adaxial and abaxial anthocyanin layers. From the fact that anthocyanins absorb green light and that the sun-adapted leaves could not use green light energy to effectively power photosynthesis, we hypothesize that the prominent adaxial anthocyanin layer effectively absorbed, and thus blocked green light from reaching the chloroplast layer. The mechanism of using green light to effectively drive photosynthesis in the shade-adapted leaves is still unclear and under investigation. However, we suspect that carotenoids and xanthophylls are playing a major role in this process.
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1 - Ithaca College, Biology, 953 Danby Road, Center for Natural Sciences, Ithaca, NY, 14850, United States
sun vs shade
Presentation Type: Poster:Posters for Sections
Location: Khorassan Ballroom/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 5:30 PM