Abstract
The identification of the limits between the cell division, elongation and mature zones in the root apex is still a matter of controversy when methods based on cellular features, molecular markers or kinematics are compared while methods based on cell length profiles have been comparatively underexplored. Segmentation models were developed to identify developmental zones within a root apex on the basis of epidermal cell length profiles. Heteroscedastic piecewise linear models were estimated for maize lateral roots of various lengths of both wild type and two mutants affected in auxin signaling (rtcs and rum-1). The outputs of these individual root analyses combined with morphological features (first root hair position and root diameter) were then globally analyzed using principal component analysis. Three zones corresponding to the division zone, the elongation zone and the mature zone were identified in most lateral roots while division zone and sometimes elongation zone were missing in arrested roots. Our results are consistent with an auxin-dependent coordination between cell flux, cell elongation and cell differentiation. The proposed segmentation models could extend our knowledge of developmental regulations in longitudinally organized plant organs such as roots, monocot leaves or internodes.
Highlights
Since the pioneering studies of Sachs (1873) and Darwin (1880), the root apex has been one of the most widely used plant organs to study cell division, cell elongation and cell differentiation which occur within successive zones (Goodwin and Stepka, 1945; Erickson and Sax, 1956b)
We identified the division zone, the elongation zone and the mature zone and checked their characteristics according to our biological assumptions
We assumed that the developmental pattern was common to the studied lateral roots even if the most rootward developmental zones were absent in some roots
Summary
Since the pioneering studies of Sachs (1873) and Darwin (1880), the root apex has been one of the most widely used plant organs to study cell division, cell elongation and cell differentiation which occur within successive zones (Goodwin and Stepka, 1945; Erickson and Sax, 1956b). Developmental Zones in Maize Lateral Roots cell division, cyclins which show marked overexpression at precise time points during the cell cycle have been used (Ferreira et al, 1994; West et al, 2004) Such type of discrete labeling leads to a probabilistic pattern and this has allowed the identification of a transition zone in the shootward region of the root apical meristem. In this zone, a progressive decrease of the occurrence of cell division is observed while cells acquire the capacity to elongate through vacuolization (Baluška et al, 1992) and cortical microtubule reorganization (Baluška et al, 1996; Baskin et al, 1999). The formation of a root hair bulge has often been taken as a marker of the switch from elongation to differentiation this tends to occur before the end of the elongation zone (Ma et al, 2003; Le et al, 2004)
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