MODULATION OF DELTA-PH-DEPENDENT NONPHOTOCHEMICAL QUENCHING OF CHLOROPHYLL FLUORESCENCE IN SPINACH-CHLOROPLASTS

The factors controlling the relationship between the formation of the transthylakoid pH gradient, as measured by quenching of 9-aminoacridine fluorescence, and the induction of non-radiative de-excitation, measured by the non-photochemical quenching of chlorophyll fluorescence, have been measured in isolated spinach thylakoids. It was found that the following are potentiators of chlorophyll fluorescence quenching: high concentrations of Mg2+; pre-illumination to induce zeaxanthin synthesis; dibucaine. These treatments tended to be antagonistic to the action of antimycin, an inhibitor of quenching, in a way consistent with the LHCII model for fluorescence quenching. The reagent dibucaine allowed quenching to occur in the absence of a pH gradient as measured by the quenching of 9-aminoacridine fluorescence and markedly increased the rate of its formation. In all of these experiments quenching was correlated with the formation of an absorbance change with a peak near 530 nm. This absorbance band was shifted from 522 nm to 530 nm in the presence of zeaxanthin.