Journal Article

Contrasting dynamics of radial O<sub>2</sub>-loss barrier induction and aerenchyma formation in rice roots of two lengths

Katsuhiro Shiono, Satoshi Ogawa, So Yamazaki, Hiroko Isoda, Tatsuhito Fujimura, Mikio Nakazono and Timothy David Colmer

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 107, issue 1, pages 89-99
Published in print January 2011 | ISSN: 0305-7364
Published online November 2010 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcq221
Contrasting dynamics of radial O2-loss barrier induction and aerenchyma formation in rice roots of two lengths

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

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Background and Aims

Many wetland species form aerenchyma and a barrier to radial O2 loss (ROL) in roots. These features enhance internal O2 diffusion to the root apex. Barrier formation in rice is induced by growth in stagnant solution, but knowledge of the dynamics of barrier induction and early anatomical changes was lacking.

Methods

ROL barrier induction in short and long roots of rice (Oryza sativa L. ‘Nipponbare’) was assessed using cylindrical root-sleeving O2 electrodes and methylene blue indicator dye for O2 leakage. Aerenchyma formation was also monitored in root cross-sections. Microstructure of hypodermal/exodermal layers was observed by transmission electron microscopy (TEM).

Key Results

In stagnant medium, barrier to ROL formation commenced in long adventitious roots within a few hours and the barrier was well formed within 24 h. By contrast, barrier formation took longer than 48 h in short roots. The timing of enhancement of aerenchyma formation was the same in short and long roots. Comparison of ROL data and subsequent methylene blue staining determined the apparent ROL threshold for the dye method, and the dye method confirmed that barrier induction was faster for long roots than for short roots. Barrier formation might be related to deposition of new electron-dense materials in the cell walls at the peripheral side of the exodermis. Histochemical staining indicated suberin depositions were enhanced prior to increases in lignin.

Conclusions

As root length affected formation of the barrier to ROL, but not aerenchyma, these two acclimations are differentially regulated in roots of rice. Moreover, ROL barrier induction occurred before histochemically detectable changes in putative suberin and lignin deposits could be seen, whereas TEM showed deposition of new electron-dense materials in exodermal cell walls, so structural changes required for barrier functioning appear to be more subtle than previously described.

Keywords: Aerenchyma; barrier to radial O2 loss; cylindrical root-sleeving O2 electrode; transmission electron microscopy; hypoxia; methylene blue; root aeration; waterlogging

Journal Article.  7567 words.  Illustrated.

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

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