MECHANISM OF NONPHOTOCHEMICAL CHLOROPHYLL FLUORESCENCE QUENCHING .2. RESOLUTION OF RAPIDLY REVERSIBLE ABSORBENCY CHANGES AT 530 NM AND FLUORESCENCE QUENCHING BY THE EFFECTS OF ANTIMYCIN, DIBUCAINE AND CATION-EXCHANGER, A23187
N. Mohanty et al., MECHANISM OF NONPHOTOCHEMICAL CHLOROPHYLL FLUORESCENCE QUENCHING .2. RESOLUTION OF RAPIDLY REVERSIBLE ABSORBENCY CHANGES AT 530 NM AND FLUORESCENCE QUENCHING BY THE EFFECTS OF ANTIMYCIN, DIBUCAINE AND CATION-EXCHANGER, A23187, Australian journal of plant physiology, 22(2), 1995, pp. 239-247
The putative relationship between the light-induced absorbance increas
e at 530 nm (Delta A(530)), the so-called light-scattering change, and
non-photochemical chlorophyll fluorescence quenching (NPQ) was examin
ed by the effect of inhibitors. Antimycin at a low concentration (350
nM) completely inhibited fluorescence quenching while only partially i
nhibiting A(530). This effect was independent of the mode of thylakoid
energisation and preinduction of violaxanthin de-epoxidation. Dibucai
ne at 20 mu M abolished NPQ but had little effect on Delta A(530). Mor
eover, the light-induced Delta A(530) Signal was present even in the a
bsence of de-epoxidised xanthophylls. The cation exchanger A23187 bloc
ked the development of NPQ as well as relaxed fluorescence quenching a
t steady state without involving a major portion of Delta A(530). Thus
, the relationship between energy-dependent A(530) changes and fluores
cence quenching was non-linear under all conditions tested. The light-
induced absorbance increase at 530 nm, therefore, is insufficient for
NPQ. The differential effects of inhibitors are explained schematicall
y, depicting three phases for NPQ: (a) formation of zeaxanthin and ant
heraxanthin by the xanthophyll cycle; (b) formation of a state reflect
ed by A(530) that is induced by the transthylakoid Delta pH, possibly
involving aggregation of LHCII; and (c) fluorescence quenching by the
combined effect of both steps and by the H+-cation exchange properties
of thylakoid membranes.