Abstract
The effects of three differently substituted pyridazinone herbicides on the accumulation of photosynthetic pigments and on the fluorescence properties of greening barley leaves were studied. The two trifluoro-methyl derivatives, SAN 6706 and 9789 caused inhibition in the accumulation of carotenes only after the first 24 h of greening. By the 48th hour of greening no detectable amounts of carotenes were present in the treated leaves. Considerable amounts of xanthophylls however remained present, and no bleaching of the leaves was observed. It is suggested that SAN 6706 and 9789 prevent the formation of the enzyme(s) catalyzing the desaturation of phytoene and phytofluene. Fluorescence spectra indicate that the organization of pigment forms altered seriously in the treated leaves. This experimental system may be useful to study the action of pyridazinone herbicides without causing complete photobleaching of the photosynthetic apparatus. SAN 9785 had only minor effects on pigment accumulation and also on the organization of pigment forms. The possible explanations of the effects observed are discussed.
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