ATP-induced increase in chlorophyll fluorescence. Characterization of rapid and slow induction phases

Abstract

The biphasic rise of chlorophyll fluorescence induced in the dark (following activation of the latent ATP-ase) upon ATP-hydrolysis was investigated in detail, yielding the following main results: (1) The rapid phase is independent of artificial reductants or redox mediators. On the contrary, the slow phase requires such additions. (2) The slow phase is selectively eliminated by substances which collapse the transmembrane proton gradient, while the rapid phase may even be stimulated. (3) The ratio of rapid-to-slow phase is favored by a high degree of chloroplast integrity. The same factors which favor the rapid phase appear to be essential for a pronounced ‘slow electrogenic reaction’ in the flash-induced P 515 absorbance change. (4) For the rapid phase of the ATP-induced fluorescence increase, neither a ΔpH nor a Δψ are obligatory intermediates. (5) Hydroxylamine at about 5 · 10 −3 M causes a preferential stimulation of the rapid phase by about a factor 2. (6) There is selective inhibition of the slow phase by DBMIB, dinitrophenylether of iodonitrothymol, Bathocuproine and HQNO (2-heptyl-4-hydroxy quinoline- N-oxide) which are known to block at the level of the Cyt b f FeS-complex. (7) The rapid phase is not affected by presence of 5 mM ferricyanide; however, there is substantial suppression if in addition a lipophilic redox mediator, like diamino-durene, is present. It is concluded that the two components of the reverse coupling reactions, reflected by the biphasic ATP-induced fluorescence rise, involve different coupling intermediates and different types of reverse electron flow. The rapid component appears to reflect close interaction between the coupling factor and a redox component in the vicinity of Photosystem II.