Control by the Embryo Axis of the Breakdown of Storage Proteins in the Endosperm of Germinated Castor BeanSeed: A Role for Gibberellic Acid

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Abstract
The embryo axis is required for the rapid breakdown of the crystalloid, albumin and lectin protein storage reserve in the endosperm of castor bean (Ricinus communis L. cv. Hale) seeds, and for the attainment of high specific activities of several endospermic proteolytic enzymes: one carboxy-peptidase and two -SH- dependent aminopeptidases. The embryo axis must be present to initiate storage protein breakdown but it is not required to maintain this process. We suggest that the embryo axis controls storage protein breakdown through the release of promoters, which can be replaced by gibberellins. Storage protein breakdown is not influenced by source-sink effects. However, the endosperm becomes sensitive to gibberellin only after an imbibition period for up to 24 h.