The simulation model of growth and cell divisions for the root apex with an apical cell in application to Azolla pinnata
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Original Article
The simulation model of growth and cell divisions for the root apex with an apical cell in application to Azolla pinnata Anna Piekarska‑Stachowiak · Jerzy Nakielski
Received: 19 March 2013 / Accepted: 16 August 2013 / Published online: 30 August 2013 © The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract In contrast to seed plants, the roots of most ferns have a single apical cell which is the ultimate source of all cells in the root. The apical cell has a tetrahedral shape and divides asymmetrically. The root cap derives from the distal division face, while merophytes derived from three proximal division faces contribute to the root proper. The merophytes are produced sequentially forming three sectors along a helix around the root axis. During development, they divide and differentiate in a predictable pattern. Such growth causes cell pattern of the root apex to be remarkably regular and self-perpetuating. The nature of this regularity remains unknown. This paper shows the 2D simulation model for growth of the root apex with the apical cell in application to Azolla pinnata. The field of growth rates of the organ, prescribed by the model, is of a tensor type (symplastic growth) and cells divide taking principal growth directions into account. The simulations show how the cell pattern in a longitudinal section of the apex develops in time. The virtual root apex grows realistically and its cell pattern is similar to that observed in anatomical sections. The simulations indicate that the cell pattern regularity results from cell divisions which are oriented with respect to principal growth directions. Such divisions are essential for maintenance of peri-anticlinal arrangement of cell walls and coordinated growth of merophytes during the development. The highly specific division program that
Electronic supplementary material The online version of this article (doi:10.1007/s00425-013-1950-9) contains supplementary material, which is available to authorized users. A. Piekarska‑Stachowiak (*) · J. Nakielski Department of Biophysics and Morphogenesis of Plants, University of Silesia, Jagiellon´ska 28, 40‑032 Katowice, Poland e-mail: [email protected]
takes place in merophytes prior to differentiation seems to be regulated at the cellular level. Keywords Apical cell · Azolla · Cell divisions · Principal directions · Root growth · Simulation model · Tensor approach Abbreviations AC Apical cell GT Growth tensor PDG Principal direction of growth Rl Relative elemental rate of linear growth Introduction Roots and shoots of pteridophytes comprise apical cells which are “stem cells” in which they renew themselves and produce a derivative every time they divide (Gunning 1982; Barlow 1997). Each derivative becomes added to the apex as a new construction unit called merophyte, within which set sequences of cell division, expansion and differentiation occur. In roots of Azolla (Gunning et al. 1978) and Equisetum (Gifford and Kurth 1982), a single apical cell (AC
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