Localization of Phenolic Compounds in the Root Cap Columella of Six-year-old Dry Seeds of Brassica napus during Imbibition and Germination

Abstract

In 6-year-old seeds of Brassica napus the columella cells have no necroses and resemble in structure the cells of the 2-year-old embryo. The outermost layer of the columella shows a structure similar to that of the lateral region of the root cap, as it contains protein bodies, rare in layers of the columella closer to the promeristem, which, in turn, contain numerous mitochondria and plastids. Phenolic compounds in the dry embryo are on the surface of the root cap in the space between the plasmalemma and the cell wall, and in small vesicles which presumably remained from degradation of ER. Imbibition promotes further extrusion of phenolics outside the plasma membrane. Long sheets of ER are visible after 9 h imbibition. After 24 h phenolics of more dense structure are localized in some dilated parts of the ER. This suggests that new production of defence compounds starts within 24 h in water, a few hours earlier than in 2-year-old seeds.