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Annals of Botany 71: 327-341, 1993
© 1993 Annals of Botany Company

The Branch Roots of Zea. 3, Vascular Connections and Bridges for Nutrient Recycling

M. E. McCully and J. E. Mallett

Department of Biology, Carleton University, Ottawa, Canada K1S 5B6

Vascular connections between branch roots and nodal roots of field-grown maize were studied by optical and electron microscopy. Their extent and openness were evaluated by locating dyes and latex particles pulled into the connections by gentle vacuum. The connecting complex is very extensive both around and along the main root. It includes rearranged and modified vascular tissues in the base of the branch within the parent cortex, small diameter tracheary elements and sieve tubes which connect the branch vascular system with the vasculature of the main root, and also interconnect the components of the latter system within those portions of the main-root vascular conduits to which the connections are made. We have named this complex the Root Vascular Plexus. Sites of direct contact of sieve tubes with tracheary elements in the vascular plexus are postulated as the sites of transfers from phloem to xylem of sugar and amino acids that have been detected in xylem exudates from maize roots. The postulate is extended to account for phloem-xylem exchange in roots of other plants where nutrient recycling has been found. It is suggested that pit membranes within the vascular plexus prevent air embolism entering main roots from the branches.Copyright 1993, 1999 Academic Press

Branch roots, phloem-xylem exchange, root vascular plexus, embolism prevention


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Home page
 Plant Physiol.Home page
M. E. McCully
Root Xylem Embolisms and Refilling. Relation to Water Potentials of Soil, Roots, and Leaves, and Osmotic Potentials of Root Xylem Sap
Plant Physiology, March 1, 1999; 119(3): 1001 - 1008.
[Abstract] [Full Text]


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