Intracellular components associated with protein synthesis in developing wheat endosperm

Abstract

Electron microscopy of thin sections of suitably treated tissue was used to investigate the fine structure of components of wheat endosperm cells which accumulate storage proteins during development. Protein-body preparations and supernatant preparations obtained by differential centrifuging of homogenates of endosperm were shown to contain different cellular components. Although some granules resembling mitochondria and areas of lipo-protein membranes were present, protein bodies were the predominant cellular components of the protein-body preparations. Lipoprotein fragments and ribosomes were present in the supernatant preparation. The fine structure of protein bodies intact tissue and of bodies obtained by ultrasonic disruption of endosperm shows that the bodies and associated ribosomes are contained within a distinctive lipoprotein membrane. Evidence is presented to show that protein bodies are formed within proteoplasts. Ribosomes isolated from the protein-body preparation have lower sedimentation coefficients than ribosomes obtained from the supernatant preparation under similar conditions. The significance of these observations is discussed. The protein-body preparations contain protein, lipid, nucleic acids and phytic acid.