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Title: EVALUATING UV-B EFFECTS AND EDU PROTECTION IN SOYBEAN LEAVES USING FLUORESCENCE EMISSION SPECTRA AND FLUORESCENCE IMAGES

Author
item MIDDLETON, ELIZABETH - NASA/GSFC
item Kim, Moon
item Krizek, Donald
item BAJWA RAVINDER, K SANDHU - BERGEN CTY ACAD

Submitted to: American Society for Photobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2005
Publication Date: 10/15/2005
Citation: Middleton, E.M., Kim, M.S., Krizek, D.T., Bajwa Ravinder, K. 2005. Evaluating uv-b effects and edu protection in soybean leaves using fluorescence emission spectra and fluorescence images. American Society for Photobiology. 81(5):1075-1085.

Interpretive Summary: The chemical, ethylenediurea (EDU) has been widely used in plant studies to protect plants against air pollution injury caused by ozone. However, little is known as to its possible protective effects against ultraviolet radiation exposure in higher plants. The present study was conducted to determine the effects of treating soybean plants with EDU or UV-B alone or a combination of UV-B and EDU. Control plants were left untreated. Fluorescence measurements, used to test stress responses in other studies, were applied to this research on EDU x UV-B interactions. By combined use of fluorescence imagery and emission spectra, we were able to obtain the first evidence for EDU protection against UV-B damage to soybean leaves. By means of fluorescence imagery and determination of emission spectra at various regions of the spectrum, it was possible to distinguish among the four combinations of stress treatments. This work compliments that done earlier in our laboratories on cucumber and is only the second study that has been reported in the literature on EDU x UV-B interactions. The findings should be of interest to researchers who are seeking non-destructive methods to evaluate environmental stress effects in higher plants.

Technical Abstract: A growth chamber experiment was conducted to evaluate whether ethylenenediurea (EDU), a chemical shown to be protective against ozone pollution, could ameliorate foliar damage induced by ultraviolet-B (UV-B) radiation exposure in ‘Roanoke’ soybean, a UV-B sensitive cultivar and whether these effects could be discriminated using fluorescence (F) observations. The experiment had four treatment groups: Control; EDU (500 umol/mol); UV-B (18 kJ/m2/d of biologically effective UV-B); and both UV-B and EDU (UV/EDU). Measurements included photosynthetic pigments, fluorescence image system (FIS) 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). Several F ratios from 280EX, 380EX, and the FIS images successfully separated the low UV vs. high EDU group responses based on means along, with intermediate values for Controls and the combined UV/EDU groups. A UV-B/blue 280EX emission ratio, F315/F420 (280EX). was correlated with chlorophyll content (ug/cm2) (r = 0.88, P<0.001) as was a ratio of emissions at two UV-A wavelengths: F330/F385 (280EX) (r = 0.87). These two 280EX ratios were also linearly correlated with emission ratios produced by 380EX, such as the far-red green ratio, F730/F525 (380EX) (r = 0.92, P<0.001), and clearly distinguished the UV-B and EDU groups separately, bracketing the intermediate responses of the UV/EDU and Control groups. The FIS images additionally captured anatomical special patterns across the leaf surfaces: (i) emissions of UV-B irradiated leaves were more uniform but lower in intensity than other groups; and (ii) emissions of EDU-treated leaves exhibited the greatest variation in spatial patterns; veins had elevated blue F and leaf edges had enhanced red and far-red F. This experiment supports the hypothesis that EDU substantially ameliorated UV-B damage to foliage, a result that relied on the combined use of FIS images and emission spectra.