Under UV excitation, leaves emit red (RF) and far red (FRF) fluorescence from chlorophyll and blue-green fluorescence (BGF) from hydroxycinnamic acids. In this study, the objective was to develop a fluorescence signature of wheat leaf aging after the appearance of the leaf. FRF and BGF were examined on the first three leaves of 2-week-old wheat plants. How FRF and BGF vary as leaf and tissue age was investigated using spectroscopic measurements, time-resolved BGF analysis, and microscopic images of the leaf surface.
FRF was found to decrease with the aging of leaves and tissues due to the accumulation of UV absorbers in the epidermis. The BGF also decreased, but with no changes in either the shape of the excitation and emission spectra or the lifetime of the fluorescence. Then, BGF emanated from the surface of the leaf, with no changes in the fluorophore composition during the aging of the leaf. The shape of the BGF spectrum indicates that ferulic acid bound to the cell wall is the major blue-green fluorophore.
The effects of pH and solvents on intact leaf GDB and ferulic acid in solution were similar, confirming the origin of hydroxycinnamic acid from GDB. Microscopic UV fluorescence images of the surface of intact leaves showed that different types of epidermal cells and sclerenchyma bands emitted BGF. The decreasing gradient of BGF from the base to the apex of the sheet could be related to the decrease in the surface of the fluorescent sclerenchyma bands. The importance of FRF and BGF as possible signatures of wheat sheet growth is discussed.
Blue-green fluorescence, ferulic acid, fluorescence microscopic imaging, foliar fluorescence, Triticum aestivum L.
Regulation of growth, development, and physiology of the whole organism