Effects of Pyridazinone Herbicides during Chloroplast Development in Detached Barley Leaves I. Effects on Pigment Accumulation and Fluorescence Properties

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