Abstract

Understanding how cell division and cell elongation influence organ growth and development is a long-standing issue in plant biology. In plant roots, most of the cell divisions occur in a short and specialized region, the root apical meristem (RAM). Although RAM activity has been suggested to be of high importance to understand how roots grow and how the cell cycle is regulated, few experimental and numeric data are currently available. The characterization of the RAM is difficult and essentially based upon cell length measurements through destructive and time-consuming microscopy approaches. Here, a new non-invasive method is described that couples infrared light imaging and kinematic analyses and that allows in vivo measurements of the RAM length. This study provides a detailed description of the RAM activity, especially in terms of cell flux and cell division rate. We focused on roots of hydroponic grown poplars and confirmed our method on maize roots. How the RAM affects root growth rate is studied by taking advantage of the high inter-individual variability of poplar root growth. An osmotic stress was applied and did not significantly affect the RAM length, highlighting its homeostasis in short to middle-term responses. The methodology described here simplifies a lot experimental procedures, allows an increase in the number of individuals that can be taken into account in experiments, and means new experiments can be formulated that allow temporal monitoring of the RAM length.

Highlights

  • Root growth takes place in the root apex, nesting both cell division and cell expansion

  • This study provides a detailed description of the root apical meristem (RAM) activity, especially in terms of cell flux and cell division rate

  • We focused on roots of hydroponic grown poplars and confirmed our method on maize roots

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Summary

Introduction

Root growth takes place in the root apex, nesting both cell division and cell expansion. As these cellular processes are both time and space separated, the zonation patterns of a root apex are classically separated into a cell division zone and an elongation zone In such patterns, the cell division zone could be defined as the root apical meristem (RAM), producing cells that are progressively pushed into the elongation zone where they stop dividing and start to rapidly increase in length. Studies of cell length profiles provided evidence that the proliferative fraction (i.e. the fraction of dividing cells) in the RAM proliferation domain is indistinguishable from one, even in response to moderate levels of stress (Baskin, 2000; Ivanov et al, 2002). Owing to the constancy of cell length in the cell proliferation domain, the RAM length is a key indicator of the number of dividing cells (Ivanov, 1997; Beemster and Baskin, 1998). The analysis of the inter-individual activity of the RAM (cell division rate and elongation rate) provided cues for a deeper understanding of the link between RAM length and root growth

Materials and methods
Results and discussion
Concluding remarks

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