|Middleton, Elizabeth - NASA/GSFC|
Submitted to: American Society for Photobiology
Publication Type: Abstract Only
Publication Acceptance Date: April 30, 2004
Publication Date: July 10, 2004
Citation: Middleton, E.M., Kim, M.S., Krizek, D.T. 2004. Evaluating UV-B effects and EDU protection in soybean leaves using fluorescence emission spectra and fluorescence images. [abstract] Program and Abstracts, Annual Meeting, American Society for Photobiology, Seattle, WA, July 10-14, 2004. p.23. Technical Abstract: A growth chamber experiment was conducted to evaluate whether ethylenenediurea (EDU), a chemical protectant, could ameliorate foliar damage induced by ultraviolet-B (UV-B) radiation exposure of a UV-B sensitive soybean cultivar (Roanoke), and whether these effects could be separated using fluorescence (F) observations taken with a fluorescence imaging system (FIS). The experiment had four treatment groups: Control (no EDU, no UV-B); EDU; UV-B; and EDU and UV-B together (EDU/UV). The EDU treatment was 500 micro-mol/mol and the UV-B exposure was 18 kJ/m2/d of biologically effective UV-B for either 3 or 10 days. Measurements included photosynthetic pigments, F images of adaxial surfaces in four spectral regions (blue, green, red, far-red), and F emission spectra of the pigment extracts produced at two excitation wavelengths, 280 nm (280EX) and 380 nm (380EX). As previously shown for cucumber, a UV-B/blue ratio of emissions at 315 and 420 nm from 280EX (F315/F420) was correlated with total photosynthetic pigment content (micro-g/cm2) (r = 0.88, P<0.001). A similar correlation was obtained using two UV-A wavelengths, F330/F385 (r = 0.87). These two ratios (F315/F420 and F330/F385) were correlated with emission ratios produced by 380EX, such as the far-red/green (F730/F525) ratio (r = 0.92. P<0.001), for which the linear response for the UV-B group was clearly distinguished from that of the EDU group and the intermediate EDU/UV and Control groups. A common response was an enhanced F for EDU and reduced F for UV-B, which occurred for green, red, and far-red images and both 280EX ratios. The images also revealed spatial patterns in leaf anatomy across the leaf surfaces. UV-B irradiated leaves produced more uniform and lower F across the leaf surfaces than other groups. FIS emissions of EDU-treated leaves were similar or higher than those in the Control group, and exhibited the greatest variation in spatial patterns: veins were clearly shown as regions of higher blue F, whereas leaf edges had enhanced red and far-red F. The intensities and spatial pattern of images in the EDU/UV group were intermediate between the UV and EDU responses. This experiment supports the hypothesis that EDU partially ameliorated UV-B damage to foliage, but also indicates that EDU induced physiological stress, a result that relied on the combined use of fluorescence images and emission spectra.