The Root Apex ofArabidopsis thalianaConsists of Four Distinct Zones of Growth Activities

Abstract

In the growing apex of Arabidopsis thaliana primary roots, cells proceed through four distinct phases of cellular activities. These zones and their boundaries can be well defined based on their characteristic cellular activities. The meristematic zone comprises, and is limited to, all cells that undergo mitotic divisions. Detailed in vivo analysis of transgenic lines reveals that, in the Columbia-0 ecotype, the meristem stretches up to 200 microm away from the junction between root and root cap (RCJ). In the transition zone, 200 to about 520 microm away from the RCJ, cells undergo physiological changes as they prepare for their fast elongation. Upon entering the transition zone, they progressively develop a central vacuole, polarize the cytoskeleton and remodel their cell walls. Cells grow slowly during this transition: it takes ten hours to triplicate cell length from 8.5 to about 35 microm in the trichoblast cell files. In the fast elongation zone, which covers the zone from 520 to about 850 microm from the RCJ, cell length quadruplicates to about 140 microm in only two hours. This is accompanied by drastic and specific cell wall alterations. Finally, root hairs fully develop in the growth terminating zone, where root cells undergo a minor elongation to reach their mature lengths.

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations

“…1A; Verbelen et al, 2006). We found that cells in the meristem and cap displayed a Ca 2+ -dependent increase in FRET efficiency in response to Glu and ATP that had similar shapes as those observed in the transition zone (Fig.…”

“…1A, white rectangular box). This region of the root has been referred to as the distal elongation zone or transition zone and is one of the proposed four distinct zones in the Arabidopsis primary root that has characteristic cellular activities (Verbelen et al, 2006). We chose this region for our initial Ca 2+ -dependent FRET efficiency measurements because it has been shown to be the most responsive to various environmental stimuli (Baluška et al, 2001;Verbelen et al, 2006).…”

“…To improve our spatial resolution and ask whether a particular [Ca 2+ ] cyt signature was associated with a more defined area of the transition zone, we used a 203 objective with a confocal zoom of 1.0. At this magnification, we were able to acquire data that covered the apical 500 mm of the primary root tip, which encompassed the cap, meristem, transition zone, and a zone before the initiating root hairs, which is likely the zone that Verbelen et al (2006) refer to as the fast elongation zone. At this low-magnification setting, we found that the biphasic [Ca 2+ ] cyt rise after Al 3+ treatment was primarily associated with the region of the root that was about 300 to 500 mm from the RCJ (Fig.…”

Cortical microtubule patterning in roots of Arabidopsis thaliana primary cell wall mutants reveals the bidirectional interplay with cell expansion

“…17 As cells acquire their final length in growth terminating zone, the newly deposited microfibrils are no more strictly transverse and thereby cortical microtubules are reoriented. 18 The supply of newly synthesized microfibrils has to keep pace with wall expansion throughout cell elongation.…”

NO signaling is a key component of the root growth response to nitrate inZea maysL.

“…In particular, the apical part (distal) of this region seems to be characterized mainly by cells that optionally can reenter the cell cycle, whereas cells of the basal (proximal) part of this zone are able to readily enter into the fast cell elongation region. 42,44,45 This developmental feature could be differentially regulated at the opposite root flanks, providing the root apices with an effective mechanism to re-orientate growth in response to environmental stimuli. 44 The transition zone is a unique zone being competent for integration of diverse endogenous and exogenous signals, and translating them into adaptive differential growth responses.…”