© 2000 Heron Publishing—Victoria, Canada
Structure–function relationships during secondary phloem development in an angiosperm tree, Aesculus hippocastanum: microtubules and cell walls
Nigel Chaffey (1, 2), Peter Barlow (2) and John Barnett (1)
1. Department of Botany, University of Reading, Reading, U.K. / 2. IACR—Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS41 9AF,
U.K. / Received April 28, 1999
Summary
We studied the dynamics of the cortical microtubule (CMT) cytoskeleton during differentiation of axial secondary phloem elements
in taproots and epicotyls of Aesculus hippocastanum L. (horse-chestnut) saplings. Indirect immunofluorescence microscopy of α-tubulin and transmission electron microscopy revealed
that fusiform cambial cells possessed a reticulum of CMTs in which individual microtubules were randomly arranged. During
differentiation of these cambial cell derivatives into secondary phloem cells, the CMTs were rearranged to become helically
oriented, regardless of phloem cell type. Although helical CMTs were a persistent feature of all axial elements of the secondary
phloem (sieve elements, companion cells, phloem parenchyma, and fiber-sclereids), some modifications of this arrangement occurred
as cells differentiated. Thus, at late stages of cell differentiation, sieve elements possessed nearly transverse CMTs, pronounced
bundling of CMTs was seen in phloem parenchyma, and the density of CMTs in the helical arrays of fibers increased markedly.
Additionally, phloem parenchyma possessed rings of CMTs in association with developing pit areas. Aspects of the development
and chemistry of cell walls were also examined during phloem cytodifferentiation.
Keywords:
cambium, cytodifferentiation, horse-chestnut, indirect immunofluorescence microscopy, sieve tube members.
