Characterization of 2S and 7S storage proteins in embryos of oil palm

Abstract

Storage proteins that accumulated during oil palm embryo development were extracted, purified and characterized. Only water- and low-salt-soluble proteins, with respective sedimentation coefficients of 2S and 7S, were detected in mature embryos. After purification by gel filtration, the various protein classes identified were characterized by electrophoresis and amino acid composition analysis. The 2S proteins comprise polypeptides of 22 kD and 19 kD, which are acidic (pI < 6) and basic (pI > 9) respectively. The 7S proteins predominate and are heterogeneous oligomers (Mr of 156 and 201 kD), comprising a polypeptide triplet of Mr between 45 and 65 kD with no disulphide bonds. Their amino acid composition is broadly similar to those of the 7S proteins of other monocotyledon embryos, but differs from those of the legume 7S vicilins. Histological examinations and electrophoresis showed that the 2S and 7S proteins appeared at the third month after fertilization, and no qualitative changes were detected up to the sixth month of embryo development. The characterization of the embryo storage proteins of oil palm is discussed with reference to legume, cereal and palm seed storage proteins. This study will enable further investigation of storage protein synthesis during somatic embryogenesis.