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Expression of α-Expansin and Xyloglucan Endotransglucosylase/Hydrolase Genes Associated with Shoot Elongation Enhanced by Anoxia, Ethylene and Carbon Dioxide in Arrowhead (Sagittaria pygmaea Miq.) Tubers
RYUTO OOKAWARA, SHIGERU SATOH, TOSHIHITO YOSHIOKA and KIMIHARU ISHIZAWA
Annals of Botany
Vol. 96, No. 4, SPECIAL ISSUE: Flooding Stress (September 2005), pp. 693-702
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42796355
Page Count: 10
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• 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 α-expansin (EXPA) and five cDNAs (SpXTH1, 2,5, 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.
Annals of Botany © 2005 Oxford University Press