INDUCTION OF 2 TYPES OF NONPHOTOCHEMICAL CHLOROPHYLL FLUORESCENCE QUENCHING IN CARBON-ASSIMILATING INTACT SPINACH-CHLOROPLASTS - THE EFFECTS OF ASCORBATE, DEEPOXIDATION, AND DIBUCAINE
N. Mohanty et Hy. Yamamoto, INDUCTION OF 2 TYPES OF NONPHOTOCHEMICAL CHLOROPHYLL FLUORESCENCE QUENCHING IN CARBON-ASSIMILATING INTACT SPINACH-CHLOROPLASTS - THE EFFECTS OF ASCORBATE, DEEPOXIDATION, AND DIBUCAINE, PLANT SCI, 115(2), 1996, pp. 267-275
We show with intact carbon-assimilating chloroplasts the induction of
two types of rapidly reversible non-photochemical fluorescence quenchi
ng, distinguishable by the effects of ascorbate, de-epoxidation and di
bucaine. In the presence of ascorbate, fluorescence quenching is anten
na type and obligatory on violaxanthin de-epoxidation; in the absence
of ascorbate, fluorescence quenching is reaction-center type and unrel
ated to violaxanthin de-epoxidation. The latter quenching type is inhi
bited by ascorbate, characterizing it as donor-side Photosystem II (PS
II) inhibition. Consistent with current concepts of down-regulation o
f PS II efficiency by non-radiative energy dissipation, both types of
quenching vary inversely to the putative ATP requirement of the carbon
-substrate accepters, although less clearly in the presence of ascorba
te, presumably due to pseudocyclic electron transport by the Mehler-as
corbate-peroxidase reaction. It is concluded from the effects of dibuc
aine that reaction-center and antenna types of quenching are related t
o protons in different thylakoid compartments, the former to domains d
e-localized in the lumen and the latter to domains localized in the me
mbrane. Antenna quenching, however, also requires lumen acidification
for the obligatory violaxanthin de-epoxidase activity. No antenna quen
ching that is unrelated to deepoxidation was observed. Since ascorbate
is usually present in leaves, these results suggest that the prevaili
ng mechanism for energy-dependent non-photochemical fluorescence quenc
hing in vivo is de-epoxidation-dependent antenna quenching.