AOBPreview originally published online on June 21, 2006
Annals of Botany 2006 98(3):565-571; doi:10.1093/aob/mcl126
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Accumulation of Glycinebetaine in Rice Plants that Overexpress Choline Monooxygenase from Spinach and Evaluation of their Tolerance to Abiotic Stress
1 Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai 981-8555, Japan and 2 Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan
* For correspondence. E-mail kishitan{at}bios.tohoku.ac.jp
Received: 9 November 2005 Returned for revision: 23 March 2006 Accepted: 13 April 2006 Published electronically: 21 June 2006
• Background and Aims Glycinebetaine (GB), a quaternary ammonium compound, is a very effective compatible solute. In higher plants, GB is synthesized from choline (Cho) via betaine aldehyde (BA). The first and second steps in the biosynthesis of GB are catalysed by choline monooxygenase (CMO) and by betaine aldehyde dehydrogenase (BADH), respectively. Rice (Oryza sativa), which has two genes for BADH, does not accumulate GB because it lacks a functional gene for CMO. Rice plants accumulate GB in the presence of exogenously applied BA, which leads to the development of a significant tolerance to salt, cold and heat stress. The goal in this study was to evaluate and to discuss the effects of endogenously accumulated GB in rice.
• Methods Transgenic rice plants that overexpressed a gene for CMO from spinach (Spinacia oleracea) were produced by Agrobacterium-mediated transformation. After Southern and western blotting analysis, GB in rice leaves was quantified by 1H-NMR spectroscopy and the tolerance of GB-accumulating plants to abiotic stress was investigated.
• Key Results Transgenic plants that had a single copy of the transgene and expressed spinach CMO accumulated GB at the level of 0·29–0·43 µmol g–1 d. wt and had enhanced tolerance to salt stress and temperature stress in the seedling stage.
• Conclusions In the CMO-expressing rice plants, the localization of spinach CMO and of endogenous BADHs might be different and/or the catalytic activity of spinach CMO in rice plants might be lower than it is in spinach. These possibilities might explain the low levels of GB in the transgenic rice plants. It was concluded that CMO-expressing rice plants were not effective for accumulation of GB and improvement of productivity.
Key words: Oryza sativa, glycinebetaine, choline monooxygenase, transgenic rice, tolerance to abiotic stress
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