Journal
ANNALS OF BOTANY
Volume 86, Issue 2, Pages 245-258Publisher
ACADEMIC PRESS LTD
DOI: 10.1006/anbo.2000.1171
Keywords
Zea mays; cryoSEM; maize; node; pits; pit membranes; vessel ends; vessels; xylem embolism; xylem pathogens
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The plexus of vascular bundles in the nodes of grasses is notoriously complex, where long axial bundles pass through a network of transverse bundles. The xylem pathways for water in maize stems have been investigated anatomically and with dye and particulate tracers, revealing some of the details of this complexity. Only approx. 3 % of axial Vessels pass through nodes without being interrupted by end wails. Axial bundles at nodes differ from those in internodes in having the metaxylem and protoxylem vessels connected by small tracheary elements. So it is only at nodes that exchange of sap occurs between the lame vessels within a bundle. End walls, acting as tilters for particles and gas bubbles, always separate axial vessels from vessels in transverse bundles. The high redundancy of bundle connections in the nodal plexus is interpreted as providing alternative water pathways to bypass embolisms and damaged or diseased sections of the xylem. The pores in the filters at the base of nodes and between axial and transverse vessels within nodes are <20 nm in diameter. Where axial Vessels connect to transverse vessels, a variety of unusual shapes of vessel elements mediate two- and three-way connections within the plexus. (C) 2000 Annals of Botany Company.
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