Quenching of excited chlorophyll A in vivo by nitrobenzene.
Nitrobenzene exerts a dual effect on the excitation of chlorophyll a(Chl a) in vivo. (a) A 3(3,4-dichlorophenyl)-1,1-dimethylurea-inhibited quenching that manifests as a partial inhibition of variable chloroplast fluorescence and of 2,6-dichlorophenol indophenol (DCPIP) photoreduction and saturates at ca. 5-10 muM. Since nitrobenzene is not a Hill oxidant, this effect is attributed to a catalyzed back flow of electrons from intersystem intermediates to pre-photosystem II oxidants. (b) A direct quenching of the excited Chl a in vivo. This effect has a threshold of ca. 100 muM nitrobenzene; at higher concentrations it leads to almost complete suppression of chloroplast fluorescence and DCPIP photoreduction. Tris-washed chloroplast enriched in the photosystem II reaction center species Z+Q- and ZQ- are nearly four times more sensitive to nitrobenzene quenching than those enriched in Z+Q. On the other hand, normal chloroplasts are about 10 to the fourth times more sensitive. Hence, it is argued that the extreme sensitivity of normal chloroplast fluorescence is not due to a preferential association of nitrobenzene with a particular redox species of the reaction center.
D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism; D004237:Diuron / Q000494:pharmacology; D007215:Indophenol; D007700:Kinetics; D009578:Nitrobenzenes; D010084:Oxidation-Reduction; D010636:Phenols; D010944:Plants; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D009578:Nitrobenzenes; D010636:Phenols; D002734:Chlorophyll; D007215:Indophenol; D004237:Diuron