The boundary of the meristematic and elongation zones in roots: endoreduplication precedes rapid cell expansion

Abstract

Plant roots consist of a meristematic zone of mitotic cells and an elongation zone of rapidly expanding cells, in which DNA replication often occurs without cell division, a process known as endoreduplication. The duration of the cell cycle and DNA replication, as measured by 5-ethynyl-2′-deoxy-uridine (EdU) incorporation, differed between the two regions (17 h in the meristematic zone, 30 h in the elongation zone). Two distinct subnuclear patterns of EdU signals, whole and speckled, marked nuclei undergoing DNA replication at early and late S phase, respectively. The boundary region between the meristematic and elongation zones was analysed by a combination of DNA replication imaging and optical estimation of the amount of DNA in each nucleus (C-value). We found a boundary cell with 4C nuclei exhibiting the whole pattern of EdU signals. Analyses of cells in the boundary region revealed that endoreduplication precedes rapid cell elongation in roots.

Longitudinal zonation pattern inArabidopsisroot tip defined by a multiple structural change algorithm

“…4H-J). Additionally, this discrepancy can be explained by the observation that in arabidopsis roots the endoreduplication cycle can also start in the EZ and that its duration is greater than that of the cell cycle in the RAM (Hayashi et al, 2013).…”

“…Hence, before rapid elongation, the symplastic nature of plant tissues yields a domain at which cells start endoreduplication but do not start rapid elongation; this region then corresponds to the TD (Baluska et al, 1996;Ivanov and Dubrovsky, 2013). Indeed, experimental evidence has shown that in arabidopsis endoreduplication precedes rapid cell elongation (Hayashi et al, 2013). Thus, for a particular cell file within the arabidopsis root, the TD can also be defined as the region where cells endoreduplicate and continue elongating at the same rate as in the PD.…”

“…As mentioned above, changes in cell proliferation are associated with the PD/TD boundary before rapid elongation starts, and particularly, before the changes in elongation rates can be detected, cells enter the endoreduplicaction cycle (Hayashi et al, 2013). Thus, we proposed that the TD can also be defined as the region where cells start endoreduplication but have not yet started rapid elongation.…”

“…This and other studies (Dello Ioio et al, 2007;Moubayidin et al, 2010;Tsukagoshi et al, 2010) do not specify how to identify the border between the PD and the TD of the RAM. Changes in cell proliferation precede the transition to rapid cell elongation: the mitotic index (percentage of dividing cells) decreases drastically (Ivanov and Dubrovsky, 2013) and endoreduplication starts (Hayashi et al, 2013). For this reason, the PD/TD boundary is associated with changes in cell proliferation, whereas the RAM/EZ boundary defines the point where a drastic shift to rapid elongation occurs.…”

Development of novel dyes and fluorescence-imaging based approaches for cellular localization and dynamics of lipid droplets

“…The assay was also used to differentiate cells in early and late Sphase in root tips of Arabidopsis seedlings (Hayashi et al, 2013). The assay was successfully applied in alfalfa suspension cultured cells and root tips (Bazin et al, 2013), tomato root tips (Ron et al, 2013;Kuznetsova & Sheval', 2013), field bean root tips (Schubert et al, 2011), asparagus cladodes (Nakayama et al, 2012), tobacco suspension cultured cells (Tresch et al, 2011), rice suspension cultured cells (Dudits et al, 2011) and maize root tips (Bass et al, 2014).…”