Lipids and their seasonal variation in the nucellar layers of Scots pine (Pinus sylvestris) seeds

The content, composition, and seasonal variation of lipids in the nucellar layers of two mature Scots pine seed lots from northern and central Finland were studied. These lipophilic layers, which are located inside the seed coat, are composed of collapsed cells and restrict the imbibition of seeds. In this study, epicuticular wax was found on their surface; in particular, the surface of the nucellar cap was composed of intermeshing wax rods. The content of total lipids of the nucellar layers varied seasonally from 10 to 24%, being highest in April. In addition to simple lipids, which formed the most abundant lipid fraction in nucellar layers, small amounts of phospho- and glyco-lipids were also present. The proportion of simple lipids and their fatty acid composition in the seeds of both provenances remained constant throughout the year, whereas seasonal variation was found in the proportions of phosphs- and glyco-lipids and in their fatty acids. In general, the variation was more marked in the northern seed lot. The unsaturated fatty acids dominated in the fractions of simple lipids and phospholipids, with linoleic acid being the most abundant single fatty acid. The saturated fatty acids with more than 22 carbon atoms were most abundant in the glycolipid fractions. The role of lipids for the function of the collapsed nucellar layers in the regulation of imbibition and germination of pine seeds is discussed.