Interactions of Lipoidal Materials and a Pyridazinone Inhibitor of Chloroplast Development

Formation of chloroplast pigments was inhibited, and free fatty acids accumulated in mustard (Brassica juncea [L.] Coss.) cotyledons and in barley (Hordeum vulgare L.) first leaves developed after treatment with 4-chloro-5- (dimethylamino)-2- (alpha, alpha, alpha-trifluoro-m-tolyl) -3 (2H) -pyridazinone. The inhibitor reduced the amount of fatty acids found in polar lipids (galactolipids) of barley chloroplasts and increased the amount in nonpolar lipids while having little effect on total content of bound fatty acids. The inhibition of chlorophyll formation was circumvented by D-alpha-tocopherol acetate, phytol, farnesol, and squalene, and by unsaturated fatty acids and their methyl esters. The protective action can be explained partially by an interaction external to the plant whereby 4-chloro-5- (dimethylamino) -2- (alpha, alpha, alpha-trifluoro-m-tolyl) -3 (2H) -pyridazinone partitioned out of the aqueous phase and into the lipid phase, thus limiting availability of the inhibitor to plants. However, the amount of inhibitor reaching the cotyledons of tocopherol-protected mustard seedlngs was still in excess of the amount necessary to cause white foliage, but it failed to produce the effect. Tocopherol treatment did not prevent the 4-chloro-5- (dimethylamino) -2- (alpha, alpha, alpha-trifluoro-m-tolyl) -3 (2H) -pyridazinone-induced buildup of fatty acids in mustard cotyledons but did partially circumvent the effect in barley leaves. The amount of linolenic acid relative to linoleic acid was reduced in barley leaves and chloroplasts by 4-chloro-5- (dimethylamino) -2- (alpha, alpha, alpha-trifluoro-m-tolyl) -3 (2H) -pyridazinone action and this effect was circumvented by tocopherol.