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

• Published in: Annals of botany Vol. 106; no. 2; pp. 277 - 284
• Main Authors: Shimamura, Satoshi, Yamamoto, Ryo, Nakamura, Takuji, Shimada, Shinji, Komatsu, Setsuko
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.08.2010
• Subjects: Aerenchyma; air; Biological Transport; Flooded soils; flooding; Floods; Glycine max - metabolism; hypertrophic lenticels; labeling techniques; Lenticels; metabolism; Microelectrodes; Original; Oxygen; Oxygen Isotopes; Oxygen Isotopes - metabolism; oxygen transport; Plant Roots; Plant Roots - metabolism; Plant Stems; Plant Stems - metabolism; Plants; root aeration; roots; sandy soils; shoots; Soil; Soil flooding; Soil water; soil waterlogging; soybean (Glycine max); Soybeans; stele; stems; submergence; Surface areas; surface water
• ISSN: 0305-7364; 1095-8290; 1095-8290
• DOI: 10.1093/aob/mcq123

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.