当前位置： SCI文献检索 > AMERICAN JOURNAL OF BOTANY期刊下所有文献 > Origins and nature of vessels in monocotyledons: 8. Orchidaceae.

Origins and nature of vessels in monocotyledons: 8. Orchidaceae.

Abstract：

:Xylem of the orchids studied provided unusually favorable material to demonstrate how conductive tissue evolves in monocotyledons. In the end walls of tracheary elements of many Orchidaceae, remnants of pit membranes were observed with scanning electron microscopy and minimally destructive methods. The full range from tracheids to vessel elements, featuring many intermediate stages, was illustrated with SEM in hand sections of fixed roots, stems, and inflorescence axes of 13 species from four subfamilies. Pit membranes in end walls of tracheary elements are porose to reticulate in roots of all species, but nonporose in stems of Cypripedioideae and Vanilloideae and porose to reticulate in stems of Orchidoideae and Epidendroideae. The distribution pattern of pit membranes and pit membrane remnants in end walls of tracheary elements of orchids parallels the findings of others. The position of Cypripedioideae and Vanilloideae as outgroups to Orchidoideae and Epidendroideae, claimed by earlier authors, is supported by clades based on molecular studies and by our studies. Little hydrolysis of pit membranes in tracheary element end walls was observed in pseudobulbs or inflorescence axes of epidendroids. The pervasiveness of network-like pit membranes of various extents and patterns in end walls of tracheary elements in Orchidaceae calls into question the traditional definitions of tracheids and vessel elements, not merely in orchids, but in angiosperms at large. These two concepts, based on light microscope studies, are blurred in light of ultrastructural studies. More importantly, the intermediate expressions of pit membranes in tracheary element end walls of Orchidaceae and some other families of angiosperms are important as indicators of steps in evolution of conduction with respect to organs (more rapid flow in roots than in succulent storage structures) and habitat (less obstruction to flow correlated with a shift from terrestrial to epiphytic).

journal_name

Am J Bot

journal_title

American journal of botany

authors

Carlquist S,Schneider EL

doi

10.3732/ajb.93.7.963

subject

Has Abstract

pub_date

2006-07-01 00:00:00

pages

963-71

issue

eissn

0002-9122

issn

1537-2197

pii

93/7/963

journal_volume

pub_type

杂志文章

在线工具

Origins and nature of vessels in monocotyledons: 8. Orchidaceae.