HERBICIDE ISOPROTURON-SPECIFIC BINDING IN THE FRESH-WATER MACROPHYTE ELODEA-DENSA - A SINGLE-CELL FLUORESCENCE STUDY

The experimental approach to the effects of the phenylurea herbicide I soproturon (IPU), on the photosynthesis activity of leaf cells of the freshwater macrophyte Elodea densa was based on the fast induction kin etics of the PSII chlorophyll a in vivo fluorescence, F-l/F-p ratios d etermined on the induction curves exhibited a noticeable effect at 5 m u g IPU . liter(-1). They appeared to be the most reliable parameter f or the quantitative evaluation of the dissociation constant of the com plex ''IPU/D-1 protein'' (K-d = 1.2 x 10(-7) M) and of the concentrati on of free IPU either at the thylakoid level or in the surrounding med ium of the leaf epithelial cells. Total IPU bioaccumulation at the who le plant level as a function of [IPU] in the medium indicated that the D-1 protein represented the main binding site for IPU in this aquatic plant species. (C) 1995 Academic Press, Inc.