Journal Article

Stem hypertrophic lenticels and secondary aerenchyma enable oxygen transport to roots of soybean in flooded soil

Satoshi Shimamura, Ryo Yamamoto, Takuji Nakamura, Shinji Shimada and Setsuko Komatsu

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 106, issue 2, pages 277-284
Published in print August 2010 | ISSN: 0305-7364
Published online August 2010 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcq123
Stem hypertrophic lenticels and secondary aerenchyma enable oxygen transport to roots of soybean in flooded soil

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Aerenchyma provides a low-resistance O2 transport pathway that enhances plant survival during soil flooding. When in flooded soil, soybean produces aerenchyma and hypertrophic stem lenticels. The aims of this study were to investigate O2 dynamics in stem aerenchyma and evaluate O2 supply via stem lenticels to the roots of soybean during soil flooding.

Methods

Oxygen dynamics in aerenchymatous stems were investigated using Clark-type O2 microelectrodes, and O2 transport to roots was evaluated using stable-isotope 18O2 as a tracer, for plants with shoots in air and roots in flooded sand or soil. Short-term experiments also assessed venting of CO2 via the stem lenticels.

Key Results

The radial distribution of the O2 partial pressure (pO2) was stable at 17 kPa in the stem aerenchyma 15 mm below the water level, but rapidly declined to 8 kPa at 200–300 µm inside the stele. Complete submergence of the hypertrophic lenticels at the stem base, with the remainder of the shoot still in air, resulted in gradual declines in pO2 in stem aerenchyma from 17·5 to 7·6 kPa at 13 mm below the water level, and from 14·7 to 6·1 kPa at 51 mm below the water level. Subsequently, re-exposure of the lenticels to air caused pO2 to increase again to 14–17 kPa at both positions within 10 min. After introducing 18O2 gas via the stem lenticels, significant 18O2 enrichment in water extracted from roots after 3 h was confirmed, suggesting that transported O2 sustained root respiration. In contrast, slight 18O2 enrichment was detected 3 h after treatment of stems that lacked aerenchyma and lenticels. Moreover, aerenchyma accelerated venting of CO2 from submerged tissues to the atmosphere.

Conclusions

Hypertrophic lenticels on the stem of soybean, just above the water surface, are entry points for O2, and these connect to aerenchyma and enable O2 transport into roots in flooded soil. Stems that develop aerenchyma thus serve as a ‘snorkel’ that enables O2 movement from air to the submerged roots.

Keywords: Aerenchyma; oxygen transport; soybean (Glycine max); flooding; root aeration; hypertrophic lenticels; soil waterlogging

Journal Article.  5701 words.  Illustrated.

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

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