a very high concentration of ionophore a23187 ( 10 microgram . 20 microgram-1 chlorophyll . ml-1 ) plus 0.1 mm edta lowers the fluorescence yield of intact chloroplasts suspended in a cation-free medium in the presence of 3- ( 3,4-dichlorophenyl ) -1,1-dimethylurea , indicating loss of divalent cation from the diffuse double layers of the thylakoid membranes .
C0007447
cation
C0007448
divalent cation