Structural characteristics of the mesophyll in some tillandsia species

Abstract

The mesophyll of 14 species of Tillandsia [T. caput-medusae, T. complanata, T. brachiavlos, T. ionantha, T. flabellata, T. fasciculata, T. latifolia, T. purpurea, T. pueblensis, T. prodigiosa, T. retorta, T. schiedeana, T. usneoides, and T. paleacea] is examined under light and electron microscopes. Primary fluorescence reveals in all the investigated species, even if they come from different habitats, the presence of a peculiar chlorophyllous tissue around vascular bundles and air cavities, and in between layers of water tissue. This arrangement helps the plant to store the water absorbed by its scales, efficiently protect the chloroplasts against intense sunlight, and prevent water loss through its air cavities. Vascular system develops by means of numerous cross anastomoses in accordance with the features of xeromorphic plants. Nevertheless, in Tillandsia this development is characterized by the scarcity of xylem elements. This fact must be considered in relation to the wide wall contacts of the mesophyll cells in these plants. Anatomohistological analysis demonstrated the association of the sheaths with vascular bundles. Besides storage and support, these sheaths also perform some additional functions. A comparison of the ultrastructure of the chloroplasts of perixylematic and periphloematic sheaths and mesophyll chloroplasts indicates morphological differences in the chlorophyllous tissue. Depending on environmental moisture, the examined species of Tillandsia adopt either CAM [Crassulacean acid metabolism] or C4 type of physiological pathway.