Dudle, Dana A. , Gould, Kevin S. .
Anthocyanins function as light attenuators in red stems of Cornus stolonifera.
Photosynthetic stems exposed to reliably strong light often produce anthocyanins in the epidermis and/or superficial cortex. Stem color varies widely among and within individuals of the same species; for example, upturned stem surfaces of red osier dogwood (Cornus stolonifera) in sunny sites are bright red, while shaded stems remain green. One functional role of red stems may be similar to that of red leaves in many species: anthocyanins act in part as light attenuators, protecting the photosynthetic apparatus from photoinhibition in stems experiencing high light and low temperatures. To test this hypothesis, we examined pigment and physiological characteristics of red and green stems from C. stolonifera and seven other species, and studied the response of red and green stems to three levels of light and cold stress using chlorophyll a fluorescence measurements. Although green and red internodes contained similar amounts of chlorophyll a and b, a comparison of light response curves revealed that electron transport rates of green stems were significantly lower than in red stems and leaves under strong white light. Green stems were more photoinhibited than red stems, and the difference was amplified in high-stress treatments. Finally, a common garden experiment demonstrated that green C. stolonifera stems exposed to full sunlight accumulated anthocyanins within four weeks, and that the fluorescence characteristics of these stems changed accordingly. Perhaps the production of stem anthocyanins, especially in prostrate stems exposed to strong sunlight for much of the day, is a strategy for long-term protection against photoinhibitory stress in photosynthetic organs that lack some of the strategies employed by “sun leaves”.
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1 - Depauw University, Department of Biology, Greencastle, Indiana, 46135, USA
2 - University of Otago, Department of Botany, P.O. Box 56, Dunedin, New Zealand
stem and leaf characteristics
Presentation Type: Oral Paper:Papers for Topics
Location: Williford C/Hilton
Date: Wednesday, July 11th, 2007
Time: 9:15 AM