Resumo

GREGO-VALENCIA, Dalia; TERRAZAS, Teresa; LARA-MARTINEZ, Reyna  e  JIMENEZ-GARCIA, Luis Felipe. The membrane of the bordered pits of two Cacteae species, Cactaceae. Bot. sci [online]. 2015, vol.93, n.2, pp.209-219. ISSN 2007-4476.  https://doi.org/10.17129/botsci.145.

In this paper pits, secondary wall, and pit membrane of tracheary elements of two species of Cactaceae with contrasting wood were characterized and compared. Mature plants of Echinocactus grusonii (dimorphic wood) and Mammillaria compressa (non-fibrous wood) belonging to the tribe Cacteae were collected and prepared using different methods to study them through photon, scanning electron, and transmission electron microscopy. Vessel elements have simple perforation plates with a border, as well as different degrees of secondary wall accumulation from annular to helical up to pseudoscalariform and alternate pits. In M. compressa secondary wall in some vessel elements may accumulate both annular and helical secondary wall. In E. grusonii pit membrane in the alternate pits of the vessel elements has very small pores, seen only at high magnification with electron microcopy. In fibers, we observed organelles, nucleus, and mitochondria, as well as an electron dense material; furthermore, the pits pair fiber-fiber has a small edge, seen with transmission electron microscopy, not described previously for the family. The pit membrane differences found between species may be related to their ability to avoid embolism, thus empiric research is needed to demonstrate it.

Palavras-chave : Cactaceae; fibers; pit; pit membrane; secondary wall; secondary xylem; vessel elements; wide-band tracheids.