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
