Détermination de différentes durées de vie de fluorescence manifestées par la chlorophylle a in vivo

A Single Pulse Picosecond Laser Study of Exciton Dynamics in Chloroplasts

“…A number of aspects of these results need to be interpreted. Perhaps the most striking result is the fact that there is no difference in the fluorescence yield curves at 685 and at 735 nm, whereas it is well known that these two emissions originate from different pigment systems, give rise to differences in low intensity fluorescence induction curves (Murata, 1968 ;Kitajima and Butler, 1975), and exhibit different singlet exciton lifetimes as determined from fluorescence decay curves (Hervo et al, 1975). Furthermore, the shape of the fluorescence yield curves as a function of the pulse energy can be interprcted in terms of either (a) the Poisson saturation model which is similar to the model proposed by Mauzerall (1976a, b) and (b) homogeneous distribution of excitons throughout the photosynthetic units and singlet-singlet exciton annihilation as described by continuum diffusion kinetics (Swenberg et al, 1976a).…”

“…The p factor takes into account final states other than singlet excitons, and collisions of excitons which do not lead to annihilation. This equation is valid for the diffusion of two excitons and annihilation within a sphere of influence R under the conditions that & R. The values of k are known to be = lo9 s-' (Hervo et al, 1975). The average intermolecular distance between chlorophyll molecules is of the order of 20A (calculated from the data of Park and Biggins (1964) from which we estimate an in uiuo chlorophyll concentration of 0.1 M ) .…”

“…The connection between the nearest neighbor hopping rate F and the diffusion coefficient D is complicated by our lack of knowledge of the degree of coherence (Pearlstein et al, 1976;Knox, 1975). However, from the temperature dependence of y and the singlet exciton lifetimes (Hervo et al, 1975), a change in D as a function of temperature of less than 30% is calculated, assuming R to be constant. Thus, D can be considered to be a constant as a function of temperature within the experimental error.…”

“…Picosecond lasers have now been used for several years in studies of the fluorescence properties of chlorophyll in uiuo (Seibert and Alfano, 1974;Yu et a!., 1975;Paschenko eta/., 1975;Beddard et a/., 1975;Campillo et al, 1976a,b;Breton and Geacintov, 1976). Unusually short fluoresence decay times have been reported with the use of ps laser pulses for excitation, which do not agree well with values obtained by more standard techniques utilizing low intensity excitation sources (Hervo et al, 1975;Briantais et al, 1972;Tumerman and Sorokin, 1967). It has been shown, however, that the fluorescence can be strongly quenched when intense laser pulses (Mauzerall, 1976a, b;Campillo et al, 1976a, b ;Breton and Geacintov, 1976;Geacintov and Breton, 1977;Monger et a/., 1976) or p s pulses (Delosme, 1972;Den Haan et a/., 1974) are utilized.…”

Picosecond fluorescence kinetics and energy transfer in chloroplasts and algae

“…These processes do not occur at the low pulse energies used for the photon-timing technique. With this technique [26,19,21] biphasic decay kinetics were found in chloroplasts and algae with lifetimes ranging from 0.2 ns for open reaction centers [19] to 0.5 to 2.0 ns for closed reaction centers [19,21]. The disparity between the 4 results of different groups, even where similar techniques were used [27], makes it difficult to relate these measurements to a model of the light harvesting mechanism.…”