LIPASE ACTIVITY AND IN-VIVO TRIACYLGLYCEROL UTILIZATION DURING PINUS-EDULIS SEED-GERMINATION

In oil seeds, triacylglycerol reserves are hydrolyzed by lipase (triacylglycerol acylhydrolase, EC 3.1.1.3), with the products being converted to sucrose for the germinating embryo. In germinating Pinus edulis Engelm. (pinyon) seed, acid lipase activity associated with the lipid bodies showed highest activity during the time of maximum triacylglycerol hydrolysis. The expression of lipase protein, determined from Western blots of electrophoretically separated lipid body proteins, increased in relation to other lipid body proteins during germination in the megagametophyte. Lipase was present, but not a major protein constituent in the embryo lipid body membrane. Triacylglycerol content in the megagametophyte and embryo of mature pinyon seed was 58% and 40% of the dry weight, respectively. Pinyon seed lipids, separated by high-performance liquid chromatography, contained seven major triacylglycerols composed of linoleic, oleic, and. palmitic acids. Lipase was not highly specific for individual triacylglycerols in vivo during germination, with all triacylglycerols depleting similarly. Overall depletion of triacylglycerols amounted to ca. 80% by 21 days in both the embryo and the megagametophyte, indicating that the initial utilization of lipid reserves occurs equally in both tissues.