Two sites of phosphatidylcholine synthesis in the wheat aleurone cell

Sub-cellular fractions from radiolabelled wheat aleurone cells were isolated using two procedures. Using both procedures, [methyl-¹⁴C]choline, was actively incorporated into phosphatidylcholine in the aleurone grain and oleosome fractions, but [U-¹⁴C]glycerol was poorly incorporated. This was most apparent in quiescent seeds and seeds incubated for 14 h or less. It is proposed that phospholipid-synthesis in the aleurone grain and oleosome fractions takes place from pre-existing storage glycerolipids. In contrast, the microsome fraction incorporated both choline and glycerol. This was more predominant in seeds incubated for 24 h or more and presumably reflects turnover of phospholipids in the endomembrane system. The relevance of these results is discussed in relation to the biogenesis of endoplasmic reticulum in germinating wheat seeds.