Chlorophyll Fluorescence

Halford Dace daceh at shrike.und.ac.za
Wed May 3 02:35:29 EST 1995


General query:

I have recently been doing some reading about chloroplast antioxidant
mechanisms and am uncertain about some aspects of the generally
accepted results of fluoresecence measurements.

Reviews such as [1] and [2] listed below describe two types of fluorescence
quenching:

Qp (Photochemical quenching) which I understand as the quenching due to
normal operation of the electron transport chain (ie reduction & reoxidation
of Qa)

and

Qnp (nonphotochemical quenching) which they attribute largely to a quantity
termed Qe (energy-dependant quenching), described as a transmembrane
delta-pH dependent quenching.  In other words, as the thylakoid lumen [H+]
increases, flourescence drops for reasons which I'm not clear about.

Can anybody enlighten me on the mechanism of Qe?  I'd really appreciate either
an explanation or a pointer to some reference.

Thanks,
Hal

References:

[1] Krause, G.H. (1988) Photoinhibition of photosynthesis.  An evaluation of
damaging and protective mechanisms.   Physiologia Plantarum 74: 566-574

[2] Foyer, C.H., Lelandais, M. and Kunert, K.J. (1994) Photooxidative stress
in plants.     Physiologia Plantarum 92: 696-717




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