Classification of the single oleosin isoform and characterization of seed oil bodies in Gymnosperms

Oleosins are hydrophobic proteins abundantly present in the oil bodies of plant seeds. Two immunologically distinct oleosins are present in seed oil bodies of diverse angiosperms, and classified as high and low M, isoforms according to their relative molecular masses in each species. Only one putative oleosin was found in seed oil bodies of three representative gymnosperm species, Pinus koraiensis, Ginkgo biloba, and Cycas revoluta. The three gymnosperm oleosins were restricted to oil bodies, as detected on immuno-assaying. Immunological cross-recognition using antibodies against the three putative gymnosperm oleosins and those against the two (high and low Mr) rice oleosin isoforms suggests that the single oleosin of pine or ginkgo is immunologically related to the low Mr isoform of angiosperms, while the single cycad oleosin is immunologically distinct from both low and high Mr isoforms of angiosperms. Oil bodies were found in embryos and megagametophytes of these three species, as observed on electron microscopy. Seed oil bodies purified from these three gymnosperms maintained their integrity via electronegative repulsion and steric hindrance on the surface of the organelles. The compositions of the three essential constituents (neutral lipid, phospholipid and protein) in seed oil bodies from these three species were determined and compared with those calculated from the oil body model proposed in angiosperms. The results suggested that seed oil bodies of gymnosperms and angiosperms possess similar surface properties and structural organization