PARENT SESSION
Oral Session #52: Plant Ecology: Light and Carbon Allocation.
Presiding: T. Day
Wednesday, August 7. 8:00 AM to 11:30 AM. Gila Meeting Room, TCC.
Photosynthetic significance and localization of ultraviolet-induced blue fluorescence in leaves.
Johnson, Gregory*,1, Day, Thomas1, 1 Arizona State University, Tempe, AZ
ABSTRACT- Ultraviolet-induced blue fluorescence is ubiquitous in leaves and is useful to remotely sense plant stress. We examined whether this UV-induced blue fluorescence could enhance the photosynthetic rate (Pn) of Sorghum bicolor leaves by constructing a polychromatic UV action spectrum for Pn using eight UV cut-off filters. The Pn averaged 4.6% higher with the UV supplement that cutoff UV below 311 nm compared to lower and higher UV-cut-off wavelengths (primarily provided more UV between 320 and 350 nm). A theoretical assessment of the potential enhancement of UV-induced blue fluorescence suggested that absorption of this fluorescence by photosynthetic pigments can enhance photosynthesis by about 1%, and that other mechanisms, such as direct absorption of UV by photosynthetic pigments, are needed to explain UV enhancements of Pn under non-saturating conditions. We also assessed the localization of blue fluorophores in three leaf regions, the cuticle, cytoplasm and covalently bound to cell walls. After the cytoplasmic extraction we found an unexpected fluorescence emission peak shift (from 439 to 471 nm), implying the presence of different cytoplasmic and wall-bound blue fluorophores. While the abaxial surface peak intensity was greater than that of the adaxial surface for fresh as well as cuticular extracted leaves, peak intensities were similar after the cytoplasmic and wall-bound extractions, which provides evidence of different concentrations of cytoplasmic blue fluorophores between the two leaf surfaces. Furthermore, whereas abaxial fluorescence peak intensity was similar among the fresh and cuticular and cytoplasmic extracted leaves, the adaxial intensity increased after cytoplasmic extraction and then dropped after wall-bound extraction, implying a greater contribution of cytoplasmic blue fluorophores to adaxial fluorescence. This surface-dependant variability may complicate remotely sensed UV-induced blue fluorescence signals and a consideration of leaf orientation may improve this approach.
KEY WORDS: remote sensing, UV-induced blue fluorescence, Sorghum bicolor, UV enhancement of photosynthesis