The Control of Food Mobilisation in Seeds of Cucumis sativus L. IV. The Pattern of Protein Degradation

Abstract

Substantial protein degradation in the cotyledons of intact cucumber seedlings is initiated in the region of the primary (central) vascular bundle. Hydrolysis in the region of the secondary vascular bundles proceeds at a slower rate. Protein is subsequently hydrolysed in the mesophyll cells between the vascular bundles in a wave of activity moving from the abaxial to abaxial surface. The palisade cells are the last to lose their storage protein. A similar pattern of degradation occurs in cotyledons excised from the embryonic axis, although the rate of degradation is slower in this treatment. Starch accumulates in excised cotyledons, particularly in the vicinity of the vascular tissues. Starch is not detectable in the cotyledons of intact seedlings.