CYTOLOGICAL ASPECTS OF THE HYPOCOTYL CORRELATED TO THE BEHAVIOR OF THE EMBRYO RADICLE OF TILLANDSIA ATMOSPHERIC SPECIES

Generally in Bromeliaceae, as in all monocotyledons, upon germination of the seed, the embryo radicle grows very little. In the atmospheric species of Tillandsia, not even this minimal growth occurs. In the adu lt stage, these species use special hairs as their sole absorbing orga n. The present work analyses the morphological and cytochemical events that are responsible for the lack of growth in the embryo radicle. Ul trastructural analysis and specific stainings for light microscopy hig hlighted a special area (that we have called the <<constriction zone>> ) in the median region of the hypocotyl-root axis of embryos of T. fla bellata Back. and T. schiedeana Steud., both atmospheric species. Duri ng the final phase of seed maturation, the cells of the aforesaid zone thickened their walls by means of materials that, at least in part, c onsisted of acid polysaccharydes and neutral lipids. These materials w ere derived from the fused contents of characteristic cytoplasmic vesi cles. Due to the presence of hydrophobic components in the walls, the cytoplasm degenerated into an amorphous mass in which polysaccharides and neutral lipids were also present. All the modifications observed s eemed to resemble certain aspects of the suberization and abscission p rocesses; consequently, the distal region of the hypocotyl-root axis r emained isolated from the proximal region. The embryo radicle did not grow at all and the isolated region remained within the integuments. B oth of these latter conditions are favorable to the life of the Tillan dsia atmospheric species, plants which must avoid any loss of trophic resources.