Alcohol‐Soluble Proteins and Protein Body Formation in the Endosperm of Tall Fescue

Abstract

Alcohol‐soluble proteins (prolamins) are the predominant storage proteins in the endosperm of most of the cereals. Prolamins are deposited within membrane bound structures called protein bodies. Our objective was to determine if there is some commonality in protein body formation between agronomically important cereals and grasses. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) of alcohol‐soluble proteins from tall rescue seeds revealed abundant proteins ranging in size from 73 to 23 kDa. Immunoblot analysis using wheat (Triticum aestivum L.) prolamin antiserum revealed limited antigenic homology between wheat and tall rescue (Festuca arundinaceae Schreb.) prolamins. The amino acid composition of tall rescue alcohol‐soluble proteins showed a high concentration of glutamine and proline residues, similar to those found in several cereal prolamins. Uitrastructural studies of the endosperm cells of tall rescue seeds at 15 d after anthesis revealed the presence of numerous vacuoles that contained protein inclusions. Extensive rough endoplasmic reticulum was seen during this developmental stage. The endoplasmic reticulum, which was often dilated, gave rise to numerous, small vacuole‐like structures. At 20 d after anthesis, the rough endoplasmic reticulum contained flocculent material within the lumen of the dilated areas. Protein aggregates were surrounded by numerous vesicles whose membranes were studded with ribosomes. Organized membrane lattices were seen at the surface of protein bodies and at the junctions where small protein bodies were fusing with larger ones. Protein A‐gold immunocytochemistry employing wheat prolamin antiserum specifically localized the alcohol‐soluble proteins within the protein bodies.