Endoplasmic Reticulum, Oleosins, and Oils in Seeds and Tapetum Cells

Abstract

Diverse organisms contain neutral lipids in subcellular particles for food reserves and other purposes. These lipid particles are present in seeds, flowers, pollen and fruit of higher plants, the vegetative and reproductive organs of primitive plants, algae, fungi, nematodes, mammalian glands and brown adipose tissue of mammals, and bacteria. Of all these lipid particles, the oil bodies (OBs) in seeds are the most prominent and best studied.Seeds of most plant species store oils (triacylglycerols [TAGs]) as a food reserve for germination and postgerminative growth. TAGs are present in small subcellular spherical OBs of approximately 1 mm in diameter. Each OB has a matrix of TAGs surrounded by a layer of phospholipids (PLs) and structural proteins termed oleosins. The small size of OBs provides a large surface area per unit TAG, which would facilitate lipase binding and lipolysis during germination. OBs inside the cells of mature seeds or in isolated preparations are remarkably stable and do not aggregate or coalesce. This stability is in contrast to the instability of artificial liposomes made from amphipathic and neutral lipids; the liposomes gradually coalesce after formation. Seed OBs are stable because their surface is shielded by a layer of oleosins. In maturing seeds, TAGs, PLs, and oleosins are synthesized in the endoplasmic reticulum (ER), from which budding OBs are released.Research on seed OBs and oleosins has been reviewed by Huang (1992, and an earlier

Oil Bodies and Oleosins in Physcomitrella Possess Characteristics Representative of Early Trends in Evolution

“…The one-cell-layer gametophyte could be observed easily with confocal microscopy for the subcellular OBs and other structures. Transient expression of various gene constructs transformed into gametophyte cells revealed that all OBs were linked to the endoplasmic reticulum (ER), that oleosins were synthesized in extended regions of the ER, and that two different oleosins were colocated in all OBs.Eukaryotes and prokaryotes contain neutral lipids in subcellular droplets as food reserves and/or for other purposes (Hsieh and Huang, 2004;Martin and Parton, 2006;Goodman, 2008;Rajakumari et al, 2008). These lipid droplets are present in seeds, pollens, fruits, and flowers of higher plants; the vegetative and reproductive organs of lower plants, algae, fungi, and nematodes; mammalian organs/tissues, such as mammalian glands and adipose tissues; and bacteria.…”

“…Eukaryotes and prokaryotes contain neutral lipids in subcellular droplets as food reserves and/or for other purposes (Hsieh and Huang, 2004;Martin and Parton, 2006;Goodman, 2008;Rajakumari et al, 2008). These lipid droplets are present in seeds, pollens, fruits, and flowers of higher plants; the vegetative and reproductive organs of lower plants, algae, fungi, and nematodes; mammalian organs/tissues, such as mammalian glands and adipose tissues; and bacteria.…”

“…These lipid droplets are present in seeds, pollens, fruits, and flowers of higher plants; the vegetative and reproductive organs of lower plants, algae, fungi, and nematodes; mammalian organs/tissues, such as mammalian glands and adipose tissues; and bacteria. Among all these lipid droplets, oil bodies (OBs) in seeds are the most prominent and have been extensively studied.Seeds of diverse plant species store oils (triacylglycerols [TAGs]) as food reserves for germination and postgermination growth (Napier et al, 1996;Frandsen et al, 2001;Murphy, 2001;Hsieh and Huang, 2004).The TAGs are present in small subcellular, spherical OBs of approximately 0.5 to 2 mm in diameter. Each OB has a matrix of TAGs surrounded by a layer of phospholipids (PLs) and the structural protein oleosins.…”

“…Tapetosomes temporarily store lipids and flavonoids, which are deposited onto the maturing pollen as a pollen coat for water-proofing and UV protection, respectively. In fruits of some species, such as olive (Olea europaea), avocado (Persea americana), and oil palm (Syagrus cocoides), the fleshy mesocarp possesses much larger (10-50-mm diameter) subcellular lipid particles of TAGs, which are devoid of surface oleosins and apparently are for attracting animals for seed dispersal (Murphy, 2001;Hsieh and Huang, 2004). OBs are also present, although generally in low abundance, in leaves of diverse plant species, and their structures and functions are unknown (Lersten et al, 2006).…”

“…Seeds of diverse plant species store oils (triacylglycerols [TAGs]) as food reserves for germination and postgermination growth (Napier et al, 1996;Frandsen et al, 2001;Murphy, 2001;Hsieh and Huang, 2004).…”