Pyridazinones chloroplasts, effects

Metflurazon inhibits photosynthesis and prevents the development of chloro-plastids in sensitive plants (Hilton et al., 1969). The authors also report on their investigation of the mode of action of 4 pyridazinone herbicides on barley. Metflurazon and its phenyl- and unsubstituted amino analogues, structurally similar to pyrazon, also inhibited the Hill reaction and photosynthesis, but showed two further biological features they resisted metabolic oxidation and inhibited chloroplast formation. The latter effect is similar to that of amitrol and dichlormate, but 100-1000 times stronger. 

Effect of substituted pyridazinones on chloroplast pigment accumulation in 4-day-old wheat shoots (2). 

Chloroplast membranes differ from most other membranes in that the major portion of the non-pigmented lipids of the chloroplast are the linolenic acid-rich galactolipids, with sulfo-lipids and phospholipids present as the minor lipid constituents. The third site of action affected by pyridazinones in wheat shoots is the formation of galactolipids (, 3 ). The data in Table III summarize the effects of substituted pyridazinones on the relative fatty acid composition of wheat shoots. 

Primary herbicidal effects are followed by secondary ones that show up before death of the plant cell. The 70-S ribosomes of wheat chloroplasts are decreased by bleaching pyridazinones in the light, but not in the dark ( 9) A prominent mode of action is observed upon the composition of fatty acids by, e.g., BAS 13338 (SAN 9785) (24, 5), which does not substcuatially interfere with carotenoid biosynthesis. Good direct inhibition of photosynthetic electron transport (I50 3 x 10 7m) is observed with the phenylpyridazinone BAS 100822 electron transport inhibition of other phenyl-pyridazinones is less than with BAS 100822 (28). 

Other laboratories have also carried out simultaneous measurements of the lipid or lipid metabolism changes associated with pyridazinone-induced in plastid morphology. Davies and Harwood examined the effects of Sandoz 6706 and Sandoz 9785 on lipid metabolism and membrane structure in greening barley. Changes seen in chloroplast structures included a slowing of normal differentiation on greening and the appearance of large... 

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