Weak Physical Adsorption Research Articles

Association of monuron in chloroplasts in relation to inhibition of hill reaction

The absorption of monuron by spinach chloroplasts from aqueous suspension medium and its relation to the inhibition of Hill reaction has been investigated using 14C-labeled monuron. Attempts were made to estimate the distribution of monuron within the chloroplast. Two compartments were found to exist for monuron absorption. The association of monuron in compartment 1 was responsible for the inhibition of Hill reaction; the compound could be removed from the chloroplast by washing, with concomitant restoration of activity. The amount of monuron absorbed by the chloroplasts correlated with the degree of inhibition regardless of oxidant (Fe(CN) 6 3−, DPIP, or NADP +) used, pH of the reaction mixture, light intensity, or chloroplast integrity. Monuron absorption by the chloroplast increased with a shift in pH of the reaction medium from 7·8 to 6·8. However, this increase of uptake was mainly due to an increase of inactive binding site. A study of the activation energy between the monuron molecule and the binding sites of the chloroplast revealed that the association was due to some very weak physical adsorption.