Evolutionary features of microspore and pollen grain development in Cyperaceae.

KEY MESSAGE: Asymmetric meiosis leading to the release of pollen grains as pseudomonads is a synapomorphy in Cyperaceae, but differences in microspore development are relevant in the family's evolutionary history. Cyperaceae members present atypical microsporogenesis, in which one meiotic product is functional while the other three degenerate, culminating in pseudomonad pollen formation. Differences during development, such as pseudomonad shape and degenerative microspore positioning, are seen throughout the family, but no phylogenetic interpretation has been made regarding these variances thus far. In this study, we analyzed the early- and late-diverging sedge genera Hypolytrum and Eleocharis, respectively, while comparing them to data available in the literature and conducting an ancestral character reconstruction for pseudomonad traits. Light microscopy results show that pseudomonad development in Hypolytrum is homologous to several other sedge genera, presenting apical degenerative microspores. However, pseudomonads are round and centrally arranged in the anther locule in this case, which consists of a pleisiomorphic trait for the family. The basal positioning of degenerative microspores is restricted to Rhynchospora, consisting of an apomorphic trait for this genus. Despite these differences, ultrastructural analysis of Eleocharis pseudomonad revealed shared features with other genera studied, which include variations in chromatin condensation and cytoplasmic turnover in functional cells. These common features seem related to the different cellular fates seen during microspore development and further corroborate the synapomorphic status of pseudomonads in sedges.

Ultrastructural analysis of Rhynchospora ovules: The first record of Cyperaceae megagametophyte on transmission electron microscope.

Microsporogenesis and microgametogenesis are unusual in sedges (Cyperaceae), the third largest monocotyledonous family, as three microspores are aborted in favor of a single functional microspore. However, studies using light microscopy show that megasporogenesis and megagametogenesis occur normally. Nevertheless, the lack of ultrastructural details limits our knowledge of female gametophyte development in this family. Given the importance of morphological studies of reproductive structures, ovules and megagametophytes of Rhynchospora pubera were analyzed under transmission electron microscopy for the first time. Overall, ovules presented features similar to those described for the family, but ultrastructural details revealed an absence of a clear boundary between the egg cell and the central cell cytoplasm. Most interestingly, antipodal and nucellar cells showed several signs of vacuolar cell death, which suggest that programmed autolysis in sporogenous and gametophytic tissue is common in gametophyte development in the Cyperaceae. This may be related to the reproductive success of this family.

Initial damage produced by a single 15-Gy x-ray irradiation to the rat calvaria skin.

BACKGROUND: Calvaria skin has a reduced thickness, and its initial damage produced by irradiation was scarcely reported. We aimed to identify the initial effects of x-ray irradiation in the rat calvaria skin. METHODS: After approval by the Animal Ethical Committee, calvaria skin sections of five Wistar rats per time point were evaluated on days 4, 9, 14, and 25 following a single 15-Gy x-ray irradiation of the head. The control group was composed of five rats and evaluated on day 4. Sections were assessed using hematoxylin-eosin and Masson's trichrome staining for morphology, inflammation, and fibrosis. Fibrosis was also evaluated by the collagen maturation index from Picrosirius red staining and by cell proliferation using the immunohistochemistry, after 5-bromo-2-deoxyuridine intraperitoneal injection. RESULTS: In irradiated rats, we observed a reduction in epithelial cell proliferation (p = 0.004) and in matrix metalloproteinase-9 expression (p < 0.001), an increase in the maturation index, and with a predominance in the type I collagen fibers, on days 9 and 14 (1.19 and 1.17, respectively). A progressive disorganization in the morphology of the collagen fibers at all time points and changes in morphology of the sebaceous gland cells and hair follicle were present until day 14. CONCLUSIONS: The initial damage produced by a single 15-Gy x-ray irradiation to the rat calvaria skin was a change in the normal morphology of collagen fibers to an amorphous aspect, a temporary absence of the sebaceous gland and hair follicles, and without a visible inflammatory process, cell proliferation, or fibrosis process in the dermis.