Light-induced decrease in DCF fluorescence of wheat leaves in the presence of salicyl hydroxamate.
5-(and-6)-Carboxy-2',7'-dichlorodihydrofluorescein diacetate (DCF-DA), a permeative indicator of oxidative stress, was loaded into dissected leaves of wheat in order to monitor the temporal development of reactive oxygen species. DCF fluorescence was found to be constant under dark conditions. Upon loading the leaves with salicyl hydroxamate, a blocker of the alternative oxidase, DCF fluorescence linearly increased in the dark. This indicates a function of alternative oxidase in preventing reactive oxygen radicals in the mitochondria. Upon illumination, the DCF signal decreased within 5 min. As illuminated chloroplasts would increase the load of reactive oxygen species, the observed decrease cannot be assigned to the production of reactive oxygen species in the chloroplasts. Three different putative mechanisms are considered which all assign an important role to light-induced delivery of NAD(P)H: (1) direct quenching of DCF fluorescence by light-generated NAD(P)H, (2) light-stimulated activation of scavenging enzymes, or (3) redirection of mitochondrial electron fluxes as caused by the delivery of excess redox equivalents (NADH) from the chloroplasts.
Hammes
E
E
Center of Biochemistry and Molecular Biology, Christian-Albrechts-Universität zu Kiel, Kiel, Federal Republic of Germany.
Hoffmann
A
A
Plieth
C
C
Hansen
U-P
UP
D002736:Chloroplasts / Q000502:physiology; D005452:Fluoresceins / Q000032:analysis; D008027:Light; D024101:Mitochondrial Proteins; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000502:physiology*; D018515:Plant Leaves / Q000737:chemistry; D010940:Plant Proteins; D017382:Reactive Oxygen Species / Q000032:analysis*; D012457:Salicylamides / Q000494:pharmacology*; D014908:Triticum / Q000737:chemistry*; D000099188:Alternative Oxidase
D005452:Fluoresceins; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D012457:Salicylamides; D000099188:Alternative Oxidase; C029569:diacetyldichlorofluorescein; C005703:salicylhydroxamic acid