AOBPreview originally published online on July 28, 2005
Annals of Botany 2005 96(4):693-702; doi:10.1093/aob/mci221
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Expression of 
-Expansin and Xyloglucan Endotransglucosylase/Hydrolase Genes Associated with Shoot Elongation Enhanced by Anoxia, Ethylene and Carbon Dioxide in Arrowhead (Sagittaria pygmaea Miq.) Tubers
1 Department of Developmental Biology and Neuroscience, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan and 2 Laboratory of Environmental Biotechnology, Graduate School of Agricultural Sciences, Tohoku University, Sendai 981-8555, Japan
* For correspondence. Present address: Miyagi University of Education, Sendai 980-0845, Japan. E-mail kimiharu{at}staff.miyakyo-u.ac.jp
Received: 30 December 2004 Returned for revision: 2 February 2005 Accepted: 22 March 2005 Published electronically: 28 July 2005
• Background and Aims Shoot elongation of arrowhead tubers (Sagittaria pygmaea Miq.) is stimulated by anoxia, ethylene and CO2. The aim of this study was to characterize anoxic elongation by comparison with elongation stimulated by ethylene and CO2.
• Methods The effects of the inhibitors aminoethoxyvinylglycine (AVG) as an ethylene biosynthesis inhibitor, 1-methylcyclopropene (1-MCP) as a potent inhibitor of ethylene action, and pyrazol, an inhibitor of alcohol dehydrogenase, on shoot elongation were examined. Moreover, the effects of these gaseous factors on expression of genes possibly involved in modification of cell wall architecture were examined by polymerase chain reaction (PCR) methods.
• Key Results and Conclusions In air, promotion by 5 % CO2 and 5 µL L–1 ethylene of shoot elongation occurred. At 1% O2, ethylene also stimulated shoot elongation but CO2 did not. Pyrazol inhibited shoot elongation in hypoxia but not in normoxia, suggesting that alcohol fermentation contributes to elongation enhanced by hypoxia. AVG and 1-MCP partially prevented shoot elongation both in normoxia and in hypoxia, but they did not have significant effects in anoxia, suggesting that endogenous ethylene acts as a stimulator of shoot elongation in normoxia and in hypoxia but not in anoxia. Ethylene is not involved in anoxia-enhanced elongation. We cloned four cDNAs (SpEXPA1, 2, 3 and 4) encoding 
-expansin (EXPA) and five cDNAs (SpXTH1, 2, 3, 4 and 5) encoding xyloglucan endotransglucosylase/hydrolase (XTH) from shoots of arrowhead tubers. The transcript levels of SpEXPA1 and 2 were increased by anoxia and those of SpEXPA2 were increased by 5 % CO2. Ethylene slightly elevated the level of SpEXPA4 transcripts. Anoxia enhanced the transcript levels of SpXTH1 and 4; neither ethylene nor CO2 had any effect. CO2 enhanced transcript levels of SpXTH3 and depressed those of SpXTH5. Ethylene decreased transcript levels of SpXTH5. These results suggest that four SpEXPA genes and five SpXTH genes are differently responsive to anoxia, CO2 and ethylene. Enhancement of SpEXPA1 and 2, and SpXTH1 and 4 transcript levels suggests that these gene products are involved in anoxic shoot elongation through modification of cell wall architecture.
Key words: Anoxia, aquatic plant, arrowhead, cell wall, cell elongation, ethylene, expansin, carbon dioxide, hypoxia, Sagittaria pygmaea, submergence, xyloglucan endotransglucosylase/hydrolase
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