lution pattern is rapidly damped out because of three transition parameters, ,, and .means that a
single reaction center does not change its redox state upon the flash (Si→Si“miss”), whereas in the
case of two oxidation steps occur within the lifetime of the flash (Si→Si 2 “double hit”). It is ob-
vious that the transition parameter is heavily dependent on the duration of the flash. Xenon flashes with
a lifetime of about 5 sec have been shown to be sufficiently short to result in little double hit contribu-
tion (~1–4%). In order to exclude this parameter properly, dye (oxazine, rhodamine, etc.) laser flashes
with a lifetime of 10 nsec have proved useful. The transition parameter finally reflects the success-
ful (intended) transition from Sito Si 1.
PHOTOSYNTHETIC GAS EXCHANGE AND RESPIRATION 305Figure 5 Absorption changes at 830 nm (left side) as a function of time and reciprocal half lifetimes as a
function of reciprocal temperature (right side) in PSII fragments from Synechococcus vulcanusCopeland. The
signal on the left side represents a trace monitored at 33°C, and the dashed curve symbolizes the data at 0°C.
The fast decay of the 830 nm absorption change due to Pheooxidation is not resolved and is symbolized by
a spike. (From Ref. 10.)
Figure 6 Typical oxygen evolution pattern induced by a train of short (5 sec) saturating light flashes fol-
lowing an extensive dark adaptation as observed with higher plant chloroplasts or green algae. (Such phe-
nomenological studies have been explained by the so-called Kok model depicted in Figure 7.) Flash frequency,
3.3 Hz; dark adaptation time, 15 min.