Journal Article

DNA replication stress induces deregulation of the cell cycle events in root meristems of <i>Allium cepa</i>

Aneta Żabka, Justyna Teresa Polit and Janusz Maszewski

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 110, issue 8, pages 1581-1591
Published in print December 2012 | ISSN: 0305-7364
Published online October 2012 | e-ISSN: 1095-8290 | DOI:
DNA replication stress induces deregulation of the cell cycle events in root meristems of Allium cepa

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry


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Background and Aims

Prolonged treatment of Allium cepa root meristems with changing concentrations of hydroxyurea (HU) results in either premature chromosome condensation or cell nuclei with an uncommon form of biphasic chromatin organization. The aim of the current study was to assess conditions that compromise cell cycle checkpoints and convert DNA replication stress into an abnormal course of mitosis.


Interphase-mitotic (IM) cells showing gradual changes of chromatin condensation were obtained following continuous 72 h treatment of seedlings with 0·75 mm HU (without renewal of the medium). HU-treated root meristems were analysed using histochemical stainings (DNA-DAPI/Feulgen; starch-iodide and DAB staining for H2O2 production), Western blotting [cyclin B-like (CBL) proteins] and immunochemistry (BrdU incorporation, detection of γ-H2AX and H3S10 phosphorylation).

Key Results

Continuous treatment of onion seedlings with a low concentration of HU results in shorter root meristems, enhanced production of H2O2, γ-phosphorylation of H2AX histones and accumulation of CBL proteins. HU-induced replication stress gives rise to axially elongated cells with half interphase/half mitotic structures (IM-cells) having both decondensed and condensed domains of chromatin. Long-term HU treatment results in cell nuclei resuming S phase with gradients of BrdU labelling. This suggests a polarized distribution of factors needed to re-initiate stalled replication forks. Furthermore, prolonged HU treatment extends both the relative time span and the spatial scale of H3S10 phosphorylation known in plants.


The minimum cell length and a threshold level of accumulated CBL proteins are both determining factors by which the nucleus attains commitment to induce an asynchronous course of chromosome condensation. Replication stress-induced alterations in an orderly route of the cell cycle events probably reflect a considerable reprogramming of metabolic functions of chromatin combined with gradients of morphological changes spread along the nucleus.

Keywords: Chromatin; cyclin B-like proteins; DNA damage; DNA replication; γ-H2AX; histone H3 phosphorylation; hydrogen peroxide; hydroxyurea; mitosis; premature chromosome condensation

Journal Article.  6726 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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