Lamellar Bodies as Intermediates in Endoplasmic Reticulum Biogenesis in Maize (Zea mays L.) Embryo, Bean (Phaseolus vulgaris L.) Cotyledon, and Pea (Pisum sativum L.) Cotyledon

Abstract

During seed germination, lamellar bodies appear within the cytoplasm of maize embryo and bean and pea cotyledon. They are most prominent when endoplasmic reticulum (ER) is increasing most rapidly. Two unit membranes from the lamellar bodies appear to act as transition cisternae to provide continuity between the lamellar bodies and the ER. The transition cisternae are smooth surfaced (without ribosomes), and the lumina are narrow. The transition between the connecting cisternae and the ER occurs abruptly over a distance of less than 0.1 .mu.m. At the region of transition, the lumen of the ER increases to a width characteristic of rough ER and ribosomes are found attached to the ER. The lamellar bodies appear to be derived from the globoids of the protein bodies, from protein bodies conjoined with lipid bodies, or perhaps both. Formation of lamellar bodies coincides with the disappearance of stored protein and lipid reserves and the formation of new ER membranes during germination. Disappearance of the lamellar bodies coincides with the cessation of rapid ER proliferation. These observations suggest that lamellar bodies function as intermediates in ER formation at the expense of the stored lipid and protein reserves in seeds. Other mechanisms of ER generation, however, cannot be excluded.