K. Wulf et Hw. Trissl, COMPETITION BETWEEN ANNIHILATION AND TRAPPING LEADS TO STRONGLY REDUCED YIELDS OF PHOTOCHEMISTRY UNDER PS-FLASH EXCITATION, Photosynthesis research, 48(1-2), 1996, pp. 255-262
Excitation of photosynthetic systems with short intense flashes is kno
wn to lead to exciton-exciton annihilation processes. Here we quantify
the effect of competition between annihilation and trapping for Photo
system II, Photosystem I (thylakoids from peas and membranes from the
cyanobacterium Synechocystis sp.), as well as for the purple bacterium
Rhodospirillum rubrum. In none of the cases it was possible to reach
complete product saturation (i.e. closure of reaction centers) even wi
th an excitation energy exceeding 10 hits per photosynthetic unit. The
parameter a: introduced by Deprez et al. ((1990) Biochim. Biophys. Ac
ta 1015: 295-303) describing the competition between exciton-exciton a
nnihilation and trapping was calculated to range between approximate t
o 4.5 (PS II) and approximate to 6 (Rs. rubrum). The rate constants fo
r bimolecular exciton-exciton annihilation ranged between (42 ps)(-1)
and (2.5 ps)(-1) for PS II and PS I-membranes of Synechocystis, respec
tively. The data are interpreted in terms of hopping times (i.e. mean
residence time of the excited state on a chromophore) according to ran
dom walk in isoenergetic antenna.