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 p lant seeds. Two immunologically distinct oleosins are present in seed oil b odies of diverse angiosperms, and classified as high and low M-r isoforms a ccording to their relative molecular masses in each species. Only one putat ive oleosin was found in seed oil bodies of three representative gymnosperm species, Pinus kouaiensis, Ginkgo biloba, and Cycas revoluta. The three gy mnosperm oleosins were restricted to oil bodies, as detected on immune-assa ying. Immunological cross-recognition using antibodies against the three pu tative gymnosperm oleosins and those against the two (high and low M-r) ric e oleosin isoforms suggests that the single oleosin of pine or ginkgo is im munologically related to the low M-r isoform of angiosperms, while the sing le cycad oleosin is immunologically distinct from both low and high M-r iso forms of angiosperms. Oil bodies were found in embryos and megagametophytes of these three species, as observed on electron microscopy. Seed oil bodie s purified from these three gymnosperms maintained their integrity via elec tronegative repulsion and steric hindrance on the surface of the organelles . The compositions of the three essential constituents (neutral lipid, phos pholipid and protein) in seed oil bodies from these three species were dete rmined and compared with those calculated from the oil body model proposed in angiosperms, The results suggested that seed oil bodies of gymnosperms a nd angiosperms possess similar surface properties and structural organizati on.