MATHEMATICAL-MODELING OF 3-(3',4'-DICHLOROPHENYL)-1,1-DIMETHYLUREA ACTION IN PLANT-LEAVES

A mathematical model of the action of a photosystem II herbicide 3-(3' ,4'-dichlorophenyl)-1,1-dimethylurea, DCMU, in plant leaves upon an ex ternal application is presented. The diffusion of DCMU in a plant tiss ue is described with the help of Fick's laws and the following reactio n of the herbicide with the Q(B)-binding site of photosystem II by the mass action theory. The model is used for a description of the effect of the herbicide on chlorophyll fluorescence induction (the O-J-I-P c urve) measured with spring barley primary leaves submerged in the herb icide solution. The increase of the J step during the herbicide action is ascribed to an increase of the number of photosystem II centres wi th bound herbicide molecules and malfunctioning in the electron transp ort to the plastoquinone pool. The experimental data were fitted with the help of the mathematical model. Values of the diffusion coefficien t and the second order rate constant of the reaction of the herbicide with photosystem II, obtained by the fitting procedure, are discussed. (C) 1998 Academic Press Limited.