<title>Detection of the in-vivo chlorophyll fluorescence spectrum: effects of environmental factors and laser excitation parameters</title>

Abstract

The laser induced chlorophyll (Chl) fluorescence in vivo at the steady state was investigated as function of the light intensity impinging on the leaf. It was used a diode laser, with pulse duration in the 10 microsecond(s) -10ms range, emitting at 635 nm, and a nitrogen-pumped dye laser, with pulse duration of 5 ns, emitting between 440 and 635 nm. With both excitation sources, it was observed that the total Chl fluorescence increases with increasing the light intensity to a maximum reached at about 300 micrometers ol m-2s-1, then it decreases to values close to the dark fluorescence F0. The Chl fluorescence spectrum was seen to vary in shape by changing the excitation wavelength from 440 to 635 nm because of change in the fluorescence reabsorption process at the 685 nm band. Light intensity at controlled temperature, the ratio between the shorter wavelength, at 685 nm, and the longer wavelength fluorescence bands, at 730 nm, as well as the total fluorescence intensity was seen to decrease with irradiation time. Decreasing the leaf temperature from 22 to 4 degrees C, at low light intensity, also induced a decrease in the F685/F730 ratio but an increase in the total fluorescence. Since photosystem I (PSI) contributes to the F730 emission band only, while photosystem II (PSII) contributes to both F685 and F730, the above evidences can be explained as due to the change with light intensity and temperature of quenching processes that affect more PSII than PSI.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.