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SIMPLE EXPLANATION OF THE MISSES IN THE COOPERATION OF CHARGES IN PHOTOSYNTHETIC O 2 EVOLUTION
Author(s) -
Delrieu MarieJose
Publication year - 1974
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1974.tb06599.x
Subject(s) - physics , yield (engineering) , photosynthesis , state (computer science) , sequence (biology) , simple (philosophy) , astrophysics , chemistry , thermodynamics , mathematics , algorithm , biochemistry , philosophy , epistemology
—In the model of Forbush et at. (1971) the observed damping of the flash yield sequence of photosynthetic O 2 evolution was related to a certain percentage of ‘misses’ (α; i.e. centers not converted). The possibility of a miss was supposed to be equal for all states S 0.1,2,3. We propose a new model and a new recurrence law that gives better quantitative agreement with the O 2 yield oscillations observed in Chlorella during a sequence of flashes. We find a better fit with all experimental results by assuming very unequal misses; the misses occur nearly exclusively on S 2 (and also sometimes on S 3 ). In the simpler case of only one miss on one state, half of S 2 exists as an inactive form S 2+ ‐ because it is in apparent equilibrium with pool A. The active form of S 2 is converted to S 3 in a flash and the unchanged inactive form S 2+ ‐ explains the miss: S1hv → S 2+ ‐ = S 2 hv → S 3 ( S 2+ ‐ is a transition state between S 1 to S 2 associated with Q ‐ ). In the dark, the apparent equilibrium constant K A between pool A and Q (i.e. S 0 , S 1 in the dark) is very large; this explains why there is no miss on these states. In light, the experimental value of K A between pool A and Q (i.e. S 2 , S 3 in the light) is 1, and this explains why the misses are large for states S 2 , S 3 ; i.e., S 2+ ‐ /S2‐ 1 and sometimes S 3+ ‐ / S 3 ˜0–1. This new model predicts that the total number of active states Σ S i = S 0 + S 1 + S 2 + S 3 is an oscillating function of the flash number. This sum 2S, is also the number of trapping centers for excitons. As fluorescence is proportional to excitons that are not trapped, our model explains why the fluorescence oscillates as a function of the flash number. We find also that the initial rates of O 2 evolution after ( n ‐ 1) flashes vs the 02 yield of the n th flash are not exactly on a straight line, which also favors our model.