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ANALYTICAL CURRENTS
Imaging fluorometer determines photosynthetic function
potential for activity of the photosynthetic Vibrational spectra apparatus, the demands of the "dark reaction," the health of the leaf, and the plant dig out buried amino adaption to environmental conditions. Be- acids cause they change quickly and are evenly distributed across the leaf, however, these Buried within hydrophobic regions of profluorescence patterns are difficult to inteins such as thioredoxin and visual rhoScientists at four Western universities terpret. dopsin, aspartic and glutamic acids are have developed a new imaging fluorescence spectrophotometer that they beDaley and colleagues used a computer- known to be protonated even at pH values of 7 and higher. Under these condilieve will improve agricultural investigainterfaced imaging spectrophotometer tions, the carbonyl stretching frequencies tions by providing information on equipped with a charge-coupled device of aspartic and glutamic acids shift to photosynthetic leaf function. Growth of camera that can acquire spectra for higher frequencies. In some cases the agricultural crops depends on appropriate 31,680 positions per sample to image carbonyl stretch may appear above 1760 irrigation, fertilization, and exterminaleaves from several types of plants grown tion; and visualization of leaves by trained in a greenhouse, including coffee, nutmeg cm-1. However, little work has been done "scouts" is commonly used to plan spray, cedar, Amaranthus cruentus, and Digiirrigation, and fertilization schedules. The talis purpurea. Two simple filters were new system, developed by Li Ning and used to remove excitation emission overLarry S. Daley of Oregon State University, lap, and software based on a novel approxGerald E. Edwards of Washington State imation was used to image the timeUniversity, Garry A. Strobel of Montana dependent fluorescence of photosystem II State University, and James B. Callis of the across the surface of the leaf. University of Washington, is based on deThe new instrument has the potential tecting the changing patterns of fluoresfor research of plant pathology and ofcence that dark-adapted photosynthetic fers numerous applied uses, say the retissues generate immediately after illumisearchers. The simple design of the sysnation. tem, compared with previous designs, The strength and composition of these should facilitate commercial production. Laboratory studies have shown that the complex fluorescence signals in a given new technique can be used to determine plant can be related to the structure and the extent of freeze damage and the impact of FT-IR spectrum of the protein thioredoxin herbicides atpH 6.5 and room temperature showing a and to detect shifted carbonyl peak of a buried amino stress inacid (inset). duced in plants under to relate these shifting carbonyl stretching attack by frequencies for aspartic and glutamic acplant pathoids with the kinds of environments found gens. The au- inside such proteins. thors have Andrei K. Dioumaev and Mark S. Braialso reconfig- man of the University of Virginia Health ured the inSciences Center tackle this problem by strument to comparing carbonyl stretching frequenimage at a cies of several simple aliphatic carboxydistance of 7 lic acids with more complex systems, such m for potenas TV-acetylaspartic acid oc-amide, in sevtial remote eral different solvents. The authors resensing apport that propionic or butyric acid are plications. good models for aspartic and glutamic (Appl. Spec- acids in these types of proteins. In nonImage of an Amaranthus cruentus leaf 12 h after exposure to a solution trosc. 1995, hydrogen-bonding solvents, the carbonyl of DCMU, an herbicide that interrupts photosynthesis. (Adapted with 49,1381-89) stretching frequency for these acids permission of the Society for Applied Spectroscopy.) Analytical Chemistry News & Features, January 1, 1996 15 A
