Ga. Johnson et al., A spectrofluorometric survey of UV-induced blue-green fluorescence in foliage of 35 species, J PLANT PHY, 156(2), 2000, pp. 242-252
Upon excitation by ultraviolet radiation (UV), plant foliage exhibits a blu
e-green fluorescence (BGF). In order to assess the prevalence and variabili
ty of this fluorescence we examined UV-induced blue-green fluorescence from
foliage surfaces of 35 species comprising seven life forms (grasses/sedges
, conifers, herbaceous dicotyledons, succulents, palms, woody deciduous dic
otyledons, and woody evergreen dicotyledons) growing in Tempe, AZ, USA. Exc
itation (260-380 nm) and emission (400-600 nm) spectra of the adaxial and a
baxial surfaces of foliage from five non-stressed plants of each species we
re measured with a spectrofluorometer. When excited with UV all species had
Violet to blue emission peaks (range = 405-475 nm; adaxial mean = 443 +/-
1 nm (SE), abaxial mean = 442 +/- 1 nm), while about a third also had a wel
l-defined green emission peak (range = 510-550 nm; adaxial mean = 523 +/- 1
nm, abaxial mean = 524 +/- 1 nm) and one species also had a yellow emissio
n peak at 568 nm. Fluorescence excitation peaks ranged from 285-370 nm (mea
n adaxial excitation peak = 342 +/- 1 nm and mean abaxial excitation peak =
341 +/- 1 nm) among surveyed species. There was a significant positive cor
relation between adaxial and abaxial excitation peak wavelengths (r = 0.66)
, as well as between adaxial and abaxial emission peak wavelengths (r = 0.9
7). To quantify and compare emission peak intensities among species we dete
rmined a fluorescence yield index (FM) calculated as the emission peak ener
gy divided by total incident excitation energy. The FM varied over an order
of magnitude among species. On average, grasses/sedges and succulents had
significantly greater FYIs than the other five life forms. The FYI of blue
(<500 nm) adaxial emission was strongly correlated (r = 0.76) with abaxial
emission. Our findings suggest BGF may be caused by several compounds in ad
dition to cell-wall-bound ferulic acid which can vary among species but app
ear to be similar on adaxial and abaxial foliage surfaces within a species.
The large range in FYI suggests some species may possess considerably grea
ter amounts of BGF compounds than others.