Role of the Endoplasmic Reticulum in Glyoxysome Formation in Castor Bean Endosperm

Homogenates of the endosperm of castor bean (Ricinus communis var. Hale) were prepared at intervals during germination and fractionated on sucrose gradients. Early in germination when glyoxysomes were being produced, a substantial proportion (50%) of the activities of malate synthetase and citrate synthetase was recovered in the membranes of the endoplasmic reticulum (mean density 1.12 grams per cubic centimeter). This proportion declined to less than 10% at 4 days when the glyoxysomes were fully developed.Gradient fractions challenged by antiglyoxysome-protein antiserum in double immunodiffusion assay revealed strong antigenic response in the endoplasmic reticulum membranes. The results support the view advanced earlier that glyoxysomes are derived directly from the endoplasmic reticulum.