Plant and Cell Physiology Advance Access originally published online on February 2, 2005
Plant and Cell Physiology 2005 46(3):505-513; doi:10.1093/pcp/pci050
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Similar Regulation Patterns of Choline Monooxygenase, Phosphoethanolamine N-Methyltransferase and S-Adenosyl-l-Methionine Synthetase in Leaves of the Halophyte Atriplex nummularia L.
1 Faculty of Agriculture, Kobe University, Nada-ku, Kobe, 657-8501 Japan
2 Graduate School of Science and Technology, Kobe University, Nada-ku, Kobe, 657-8501 Japan
3 Corresponding author: E-mail, yastak{at}kobe-u.ac.jp; Fax, +81-78-803-5857.
Glycinebetaine (betaine) highly accumulates as a compatible solute in certain plants and has been considered to play a role in the protection from salt stress. The betaine biosynthesis pathway of betaine-accumulating plants involves choline monooxygenase (CMO) as the key enzyme and phosphoethanolamine N-methyltransferase (PEAMT), which require S-adenosyl-l-methionine (SAM) as a methyl donor. SAM is synthesized by SAM synthetase (SAMS), and is needed not only for betaine synthesis but also for the synthesis of other compounds, especially lignin. We cloned CMO, PEAMT and SAMS isogenes from a halophyte Atriplex nummularia L. (Chenopodiaceous). The transcript and protein levels of CMO were much higher in leaves and stems than in roots, suggesting that betaine is synthesized mainly in the shoot. The regulation patterns of transcripts for SAMS and PEAMT highly resembled that of CMO in the leaves during and after relief from salt stress, and on a diurnal rhythm. In the leaves, the betaine content was increased but the lignin content was not changed by salt stress. These results suggest that the transcript levels of SAMS are co-regulated with those of PEAMT and CMO to supply SAM for betaine synthesis in the leaves.
The nucleotide sequences reported in this paper has been submitted to DDBJ under accession numbers AB183561
Received July 21, 2004; Accepted December 30, 2004
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