The relationship between the capacity to evolve oxygen and the variable fluorescence of chlorophyll after microsecond illumination in Chlorella, pea leaves and pea thylakoids.
The relationship between the capacity to evolve oxygen following a flash of a few microseconds duration and the variable fluorescence of chlorophyll was determined in Chlorella, leaf disks of peas, and thylakoids of pea leaves. It was found that this relationship is linear in intact plant material, while it is nonlinear in thylakoids. However, in thylakoids, the recovery of the capacity to evolve oxygen does not track the decay of the variable yield of Chl a fluorescence. This nonlinear relationship in thylakoids results from a reduced rate in the oxygen evolution reaction with no change in the decay of the variable yield of Chl a fluorescence. From a new application of the matrix analysis method to oxygen flash yields, the S1'-->S2, S2'-->S3 and S3'-->S4-->S0 transitions are found to be slowed or delayed in pea thylakoids and this underlies the slower rate of the recovery of the capacity to evolve oxygen in thylakoids. It is concluded that in intact cells the QA-QB(-)-->QA QB- reaction was rate-limiting for the recovery of the capacity to evolve oxygen, the equal energy-transfer hypothesis and the sequential double-hit model are valid in pea leaves and that the apparent invalidity in thylakoids is actually due to slowing of reaction steps in the oxygen evolution mechanism.
Jursinic
P A
PA
Department of Medical Physics, University of Wisconsin, Madison 53706.
Dennenberg
R J
RJ
D002708:Chlorella / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism*; D007887:Fabaceae / Q000378:metabolism*; D005453:Fluorescence; D008433:Mathematics; D010100:Oxygen / Q000378:metabolism*; D010946:Plants, Medicinal
D002734:Chlorophyll; D010100:Oxygen