The in vivo Chl-a fluorescence includes two components: so-called 
’constant’ ($> ) and ’variable’ (or recombinational) ( 4 > ) ones (see, e.g. 
Krause and Weis, 1991). While $ yield is independent on the functional state 
C 
of PSII RCs and electron-transport chain, the yield of $ strongly depends on 
V 
it. The ratio $ /$ may vary from 0 (all RCs are open, or active) up to 2-4 
V C 
(all RCs are in closed state). 
3. - THEORETICAL DESCRIPTION OF LIF FROM CHLOROPHYLL IV VIVO 
The problem of adequate description of energy migration in primary photo 
synthesis processes due to powerful pulsed laser excitation is often under 
estimated. We have developed and tested experimentally the model describing 
these processes and Chl-a fluorescence emission caused by nanosecond laser 
pulses (such lasers are most often used in lidar systems). This model takes 
into account the exciton migration between various photosynthetic units, 
monomolecular exciton decay processes, bimolecular annihilation of excitons, 
pigment bleaching, and changes in functional state of PS II RCs caused by 
environmental influences and laser pulse action (Bunin et al., 1992). 
+ Four jiiff^rent states of PS II RC are considered in the model: PIQ, 
P IQ , PIQ , P I Q (where P is the primary donor P680 , I the intermediate 
pheophytin acceptor, and Q the first quinone acceptor of PS II RC). The 
concentrations of these RCs states are marked in N , N , N , N respectively. 
12 3 4 
The model is described by the following kinetic equations: 
dn 
dt 
dN 
1 
dt 
dt 
d t 
dN 
± 
dt 
F=F{ t,r) is the photon flux density of laser excitation; o* is the effective 
absorption cross-section of Chl-a molecules that takes into account the 
contribution of accessory pigments (chlorophyll-b or chlorophyll-c, and 
carotenoids) at the wavelength of laser excitation; n - the concentration of 
Chl-a molecules excited states; n - the total concentration of Chl-a 
o 
molecules; N = N +N +N +N - the total concentration of RCs in the 
0 12 3 4 
light-harvesting antenna; p (i=l,..,4) - the rates of linear deactivation of 
i 
excitons corresponding to different states of PS II RC; p^ c - the rate of 
excitons trapping by RCs; p - the rate of charges recombination in close RC; 
r 
y - the constant of singlet-singlet excitons annihilation. 
Saturation curves (dependencies of fluorescence intensity I fi (and yield 
I fi /I) on laser intensity I) were calculated for both ’constant’ and 
’variable’ components of in vivo Chl-a fluorescence. Comparison of theoretical 
F o • (n -n) - E p. • n- 
i =i 1 
•n‘ + 5' ' P, 
RC „ 
- P, -n. 
dN 
dt 
RC . 
- p 3 * n ’ 
dN 
XT + P • N 
N r 4 
0 
dt