INDUCTION OF 2 TYPES OF NONPHOTOCHEMICAL CHLOROPHYLL FLUORESCENCE QUENCHING IN CARBON-ASSIMILATING INTACT SPINACH-CHLOROPLASTS - THE EFFECTS OF ASCORBATE, DEEPOXIDATION, AND DIBUCAINE

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.