871 
flavonoids of the vacuole or phenolic acids of the cell wall. Total fluorescence of intact leaves is strongly 
influenced by these fluorophores of the epidermal layer (including cuticle) precluding the investigation on 
changes of mesophyllic fluorophores especially in the blue part of the spectrum. Because of the blue 
fluorescence of the epidermis, the blue/green ratio proposed as a stress signature [8] would reflect mainly 
changes in epidermal phenolics. 
TABLE 1. RELATIVE INTENSITY OF BLUE AND RED FLUORESCENCE SIGNALS 
conditions: Nanosecond pulsed fluorimeter [ 32] 
Fvcitation N 2 laser: 337 ran Analysis : wide-band filter (400-580 nm) 
Material• Spinach (Chi content = 35 nmol/cm^) 
FLUORESCENCE 
RED 
BLUE 
whole leaf 
100 
100 
leaf without epidermis 
397 
77 
Isolated intact chloroplasts 
466 
15 
Taking into account that the variable BF represents = 50% of the total BF on isolated chloroplasts, it is 
concluded that the light induced variable BF on intact leaves is < 2-3 % of the total blue emission. 
2.0 
16 g. 
a 
1.2 o 
H 
8 
0.4 £ 
200 400 600 
time(s) 
-200 0 
200 400 600 
hrne(s) 
800 
0.0 
1000 
FIG. 9 A. Effect of low and high intensity actinic light on blue (full line) and red (broken line) fluorescence in 
intact isolated chloroplasts. Intact chloroplasts at a concentration of 2.7 pmol Chi ml'l (27 nmol Chi cm‘2) were 
illuminated in the resuspending medium. After [32]. 
FIG. 9 B. Light induced change in blue and red fluorescence in leaves. Lower epidermis was striped away from 
a mature spinach leaf and a small rectangle placed in the sample chamber. The free mesophyll (abaxial) side was 
turned towards the laser beam. Light intensity like in Fig. 9 A. After [32] 
It is worth noting that according to [31] the possibility exists to measure the redox state of nucleotides 
in an intact leaf. The proposed approach requires appropriate time windows in order to isolate the 3 and 9 ns 
components, combined with actinic light-induced variable fluorescence [32]. In these conditions, the ratio of the 
two fluorescent components could provide an information on the redox state of the leaf. This can be done at a 
single wavelength, in the green, which eliminates the problem of reabsorption by the omnipresent chlorophyll. 
8 . CONCLUSION 
The results presented here show that, with a special method of deconvolution, remote sensing of the 
fluorescence lifetime can be performed on plant canopies with a laser instrumentation. They also shows that 
information about the relatives positions of leaves inside the canopy can be extracted from the back scattered 
signal. This information would provide helpful data to canopy models developed for the understanding of 
interactions between vegetation and its environment [29, 30]. Fluorescence lifetime measurement on canopies 
offers new perspectives for vegetation monitoring on a large scale, because it is closely related to photosynthetic 
activity. Experiments are now being performed with this new type of picosecond LIDAR and are mainly 
focused on the developement of methods for the assessment of plant status.