Fat Metabolism in Higher Plants: XL. Synthesis of Fatty Acids in the Initial Stage of Seed Germination.

To understand more fully organelle membrane assemblage, the synthesis of the first fatty acids by the germinating pea, Pisum sativum, was studied by the incorporation of either tritiated water or acetate-1-(14)C into lipids by the intact, initially dry seed. After a lag phase, labeling proceeded linearly. This lag phase ended when uptake of water had increased the seed weight to 185% of its original weight. The first fatty acids synthesized were palmitic and stearic followed shortly after by long chain saturated fatty acids (C(20)-C(26)). The synthesis of very long chain acids was consistently characteristic of several other seeds in early stages of germination. The majority of the radioactive acids were present in phospholipids and were localized in particulate fractions. The acyl components of phosphatidyl glycerol were highly labeled. The very long chain acids were found predominantly in the waxes. Pulse labeling indicated little turnover of the labeled fatty acids. Evidence is presented indicating that the enzymes for fatty acid synthesis are already present in the dry seed and participate in the synthesis of fatty acids once a critical water content of the seed is achieved.