Authors: Ray F Evert William A Russin C E J Botha
Publish Date: 2017/03/18
Volume: 198, Issue: 4, Pages: 572-579
Abstract
Large intermediate and small bundles and contiguous tissues of the leaf blade of Hordeum tvulgare L ‘Morex’ were examined with the transmission electron microscope to determine their cellular composition and the distribution and frequency of the plasmodesmata between the various cell combinations Plasmodesmata are abundant at the mesophyll/parenchymatous bundle sheath parenchymatous bundle sheath/mestome sheath and mestome sheath/vascular parenchyma cell interfaces Within the bundles plasmodesmata are also abundant between vascular parenchyma cells which occupy most of the interface between the sieve tubecompanion cell complexes and the mestome sheath Other vascular parenchyma cells commonly separate the thickwalled sieve tubes from the sieve tubecompanion cell complexes Plasmodesmatal frequencies between all remaining cell combinations of the vascular tissues are very low even between the thinwalled sieve tubes and their associated companion cells Both the sieve tubecompanion cell complexes and the thickwalled sieve tubes which lack companion cells are virtually isolated symplastically from the rest of the leaf Data on plamodesmatal frequency between protophloem sieve tubes and other cell types in intermediate and large bundles indicate that they and their associated companion cells when present are also isolated symplastically from the rest of the leaf Collectively these data indicate that both phloem loading and unloading in the barley leaf involve apoplastic mechanismsThe authors thank Susan E Eichhorn for assistance in preparation of the manuscript including the figures and typing Dr Joanne M Dannenhoffer for Fig 1 and Kandis Elliot for assistance with graphic design This study was supported by National Science Foundation Grant No IBN9001759 and Grant No IBN9320218 to RFE
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