Sv. Mantha et al., Evidence from action and fluorescence spectra that UV-induced violet-blue-green fluorescence enhances leaf photosynthesis, PHOTOCHEM P, 73(3), 2001, pp. 249-256
We assessed the contribution of W-induced violet-blue-green leaf fluorescen
ce to photosynthesis in Poa annua, Sorghum halepense and Nerium oleander by
measuring UV-induced fluorescence spectra (280-380 nm excitation, 400-550
nm emission) from leaf surfaces and determining the monochromatic UV action
spectra for leaf photosynthetic O-2-evolution, Peak fluorescence emission
wavelengths from leaf surfaces ranged from violet (408 nm) to blue (448 nn)
, while excitation peaks for these maxima ranged from 333 to 344 nm, Action
spectra were developed by supplementing monochromatic radiation from 280 t
o 440 nm, in 20 nm increments, to a visible nonsaturating background of 500
mu mol m(-2) s(-1) photosynthetically active radiation and measuring photo
synthetic O-2-evolution rates. Photosynthetic rates tended to be higher wit
h the 340 nm supplement than with higher or lower wavelength UV supplements
. Comparing photosynthetic rates with the 340 nm supplement to those with t
he 400 nm supplement, the percentage enhancement in photosynthetic rates at
340 nm ranged from 7.8 to 9.8%. We suspect that 340 nm UV improves photosy
nthetic rates via fluorescence that provides violet-blue-green photons for
photosynthetic energy conversion because (1) the peak excitation wavelength
(340 nm) for violet-blue-green fluorescence from leaves was also the most
effective UV wavelength at enhancing photosynthetic rates, and (2) the magn
itude of photosynthetic enhancements attributable to supplemental 340 nm UV
was well correlated (R-2 = 0.90) with the apparent intensity of 340 nm UV-
induced violet-blue-green fluorescence emission from leaves.