Ultrastructural studies on bicellular pollen grains of Tillandsia seleriana Mez (Bromeliaceae), a neotropical epiphyte

The ultrastructure and ontogeny of bicellular pollen in Tillandsia seleriana Mez (Bromeliaceae) before anther dehiscence has been here investigated. The development, after the first mitosis, is described to consist in three stages. The aim of the present report, which is part of a more extensive study on the reproductive mechanisms in the genus, is to compare the development of the male gametophyte of Tillands with information available from other an- giosperms. Aspects on water, starch and soluble carbohydrate contents of the pollen of T. seleriana are discussed in the light of the current ecological classification of pollens. The generative cell did not show any plastid in its cyto- plasm, hence plastid inheritance in Tillandsia is confirmed as totally maternal (Lycopersicon type). Contrarily to other pollen grains, those of T. seleriana maintain a considerable amount of starch in the vegetative cell until dehis- cence. The inulin test was negative, indicating that T. seleriana pollen lacks of Fructans. Pollen only with starch is subjected to faster dehydration and, probably, cannot be transported at long distance. The ecological adaptive plas- ticity of genus Tillandsia, is confirmed also by morphological characters that appear to be typical both of the partially dehydrated and partially hydrated pollen in T. seleriana. This situation is, probably, a plesiomorphic character that permitted to genus Tillandsia to differentiate species well adapted to arid environments and others living in mesic forests.