Santos 2015 (Conference Paper) Dyckia

Pollen ultrastructure of Dyckia distachya (Bromeliaceae)

Author(s):—R. Santos & J.E. Mariath in Benko-Iseppon, A.M.; Alves, M. & Louzada, R. (2015) An overview and abstracts of the First World Congress on Bromeliaceae Evolution. Rodriguésia 66(2): A1-A66.

Publication:— (2015).

Abstract:—Dyckia Schult. & Schult. is the second largest genus of bromeliads within the subfamily Pitcairnioideae, comprising 159 xerophytic species, terrestrial or rupicolous. In South America, the genus occurs in all regions of Brazil, Uruguay, Argentina, Bolivia, and Paraguay. Although there are many palynological studies of Dyckiaspecies, little is known about the cytology of the male gametophyte. In this work, we analyze the pollen grain ultrastructure of D. distachya Hassler, a rheophytic and endemic species of the Uruguay River Basin, which is listed as critically endangered. For ultrastructural analysis, sample preparation was performed using a microwave processor. Dehiscent anthers of D. distachya were macerated to release pollen in the primary fixative solution containing 2.5% glutaraldehyde and 2.0% formaldehyde, postfixed in a mixture of 1% OsO4and 0.8% K3[Fe(CN)6], dehydrated in an ascending acetone series, embedded in Spurr?s low-viscosity epoxy resin, and polymerized in an oven at 60°C. Ultrathin sections were contrasted with a modified Thiéry reaction followed by lead solution, and observed in a transmission electron microscope at 80 kV. In addition, for the isolation of generative cells, fresh pollen grains were squashed on glass microscope slides in a drop of 20% sucrose and immediately visualized under interferential Nomarski contrast. The mature male gametophyte of D. distackia is bicellular. The vegetative cell is rich in dictyosomes, mitochondria, smooth endoplasmic reticulum, lipid droplets, and amyloplasts containing small starch grains. The vegetative nucleus presents an amoeboid contour and is located in the cytoplasmic zone opposite the aperture, near the sporoderm, where thereis an abundance of rough endoplasmic reticulum. The vegetative nucleus partially surrounds the generative cell, giving rise to the male germ unit. The elongated generative cell is striated, delimited by a periplasmic space, and contains cortical microtubules. The generative cell is remarkably equipped with two tails, which when seen in isolated generative cells, give the cell a length of more than 70 micrometers. However, inside the vegetative cytoplasm, the tails are highly sinuous and limited to the vicinity of the vegetative nucleus. Thegenerative nucleus also has an amoeboid shape. This is the first description of the presence of two long tails in the generative cell of the Bromeliaceae. Its functional role is still unknown as a structural association was not observed between these terminal cell portions and the vegetative nucleus. However, the behavior of the generative cell along the pollen tube should be analyzed, as in this behavior the cell tails may be important.
These early results point to the need for a wide comparative analysis of the structure of the male gametophyte
in the Bromeliaceae, which should present a variety of characteristics useful in providing a better understanding
of the evolution and phylogenetic relationships of the bromeliads.

Keywords:—Male Germ Unit; Generative Cell; Vegetative Cell.