INTERACTION OF THE PHOTOSYNTHETIC AND RESPIRATORY ELECTRON-TRANSPORT CHAINS PRODUCING SLOW O-2 SIGNALS UNDER FLASHING LIGHT IN SYNECHOCYSTIS SP PCC-6803
Pc. Meunier et al., INTERACTION OF THE PHOTOSYNTHETIC AND RESPIRATORY ELECTRON-TRANSPORT CHAINS PRODUCING SLOW O-2 SIGNALS UNDER FLASHING LIGHT IN SYNECHOCYSTIS SP PCC-6803, Photosynthesis research, 45(1), 1995, pp. 31-40
We investigated the slow signal of apparent O-2 release under brief li
ght flashes by using mutants of Synechocystis sp. PCC 6803 which lacke
d CP43 and D1. The slow signal was present at higher amplitudes in the
mutants. It was inhibited by starving the mutants of glucose (>90%),
by 10 mM NaN3 (85%) and by boiling samples for 2 min (100%). In the mu
tants and in the wild-type, the slow signal was 95% inhibited by the c
ombination of DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone)
and HQNO (2-n-heptyl-4-hydroxyquinoline-N-oxide). In the wild type, th
e addition of DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) or CCCP (
carbonylcyanide m-chlorophenylhydrazone) completely inhibited photosyn
thetic O-2 evolution, yet failed to inhibit the slow signal. We explai
n the kinetics of the wild-type signal as a positive deflection due to
the inhibition of respiration by PS I activity, and a negative deflec
tion due to the stimulation of respiration by electrons originating fr
om PS II. We found no evidence of a 'meta-stable S-3' in Synechocystis
sp. PCC 6803 that could contribute to the slow signal of apparent O-2
release. We present a calculation which involves only averaging, divi
sion and subtraction, that can remove the contribution of the slow sig
nal from the true photosynthetic O-2 Signal and provide up to a 10-fol
d improved accuracy of the S-state models.