ISSN:
1615-6102
Keywords:
Allium cepa
;
Apical meristem
;
Pericycle cell types
;
Transversal growth
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary In the apical meristem of the adventitious root ofAllium cepa, all pericycle cells show a marked increase in cross-sectional area between 400 and 800 μm behind the tip, this transversal growth ceasing in the 1,200–1,400 μm interval. However, different pericycle cell types (opposite xylem, intervening and opposite phloem) show different transversal growth kinetics. Along the meristem, the opposite xylem cells are narrower than both the intervening and opposite phloem cells, and these latter are similar in cross-sectional area. Another relevant difference is in the polarity of the transversal expansion, which in turn gives rise to changes in cell shape. In fact, in apical most portions of the meristem, the opposite phloem cells mainly expand tangentially, while the intervening cells do so radially, and the opposite xylem cells undergo a similar tangential and radial expansion. By contrast, in basal most portions of the meristem, radial expansion continues in the opposite phloem cells when it has ceased in the intervening cells. These latter expand tangentially once again when tangential expansion has ceased in the opposite phloem cells. As a consequence of this transversal growth, the opposite xylem cells, which can initiate lateral root primordia, retain their isodiametric transversal shape along the meristem, whereas the transversal shape of the opposite phloem and intervening cells initially changes from isodiametric to markedly enlarged tangentially (opposite phloem) or radially (intervening), after which both cell types tend to become more rounded in shape.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01539962
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