UV band fluorescence (in vivo) and its implications for the remote assessment of nitrogen supply in vegetation

When excited at 280 nm, intact vegetation produced two overlapping broadband fluorescence emissions; the first centered near 335 nm [ultraviolet` (UV) band], and the second centered near 440 urn (blue band). Separation of these two fluorescence bands was achieved by an iterative nonlinear curve fit procedure utilizing the asymmetric double sigmoidal spectral function. The subsequent ratio of the deconvoluted curve intensities exhibited a significant relation between protein concentration and fluorescence. UV band fluorescence from vegetation treated with varying levels of nitrogen fertilization decreased relative to the blue fluorescence as a function of protein levels. These studies indicate that in vivo UV band fluorescence can be utilized as a nondestructive tool to remotely sense variations in protein concentration due to nitrogen supply. Strong similarities were noted in the UV band fluorescence characteristics of intact vegetation to both membrane-bound and soluble plant proteins containing aromatic amino acids. Pure ribulose 1,5-bisphosphate carboxylase in aqueous solution exhibited UV fluorescence characteristics with excitation and emission distributions similar to those of intact vegetation. Because of its high concentration (up to 70% of the soluble leaf proteins), we believe this protein contributes to the UV band fluorescence emanating from the intact leaf. In addition, similar fluorescence characteristics were observed for two other prominent enzymatic plant proteins; namely, adenosine 5′-tri-phosphatase and carboxylase phosphoenolpyruvate carboxylase. These results indicate that UV band fluorescence emanating from the intact leaf could originate from several plant proteins that contain aromatic amino acids.