PLANT PHYSIOLOGY , Vol 110, Issue 4 1301-1308, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Betaine Aldehyde Dehydrogenase in Sorghum (Molecular Cloning and Expression of Two Related Genes)
A. J. Wood, H. Saneoka, D. Rhodes, R. J. Joly and P. B. Goldsbrough
Department of Horticulture, Purdue University, West Lafayette, Indiana 47907-1165 (A.J.W., D.R., R.J.J., P.B.G.)
The ability to synthesize and accumulate glycine betaine is wide-spread
among angiosperms and is thought to contribute to salt and drought
tolerance. In plants glycine betaine is synthesized by the two-step
oxidation of choline via the intermediate betaine aldehyde, catalyzed by
choline monooxygenase and betaine aldehyde dehydrogenase (BADH). Two
sorghum (Sorghum bicolor) cDNA clones, BADH1 and BADH15, putatively
encoding betaine aldehyde dehydrogenase were isolated and characterized.
BADH1 is a truncated cDNA of 1391 bp. BADH15 is a full-length cDNA clone,
1812 bp in length, predicted to encode a protein of 53.6 kD. The predicted
amino acid sequences of BADH1 and BADH15 share significant homology with
other plant BADHs. The effects of water deficit on BADH mRNA expression,
leaf water relations, and glycine betaine accumulation were investigated in
leaves of preflowering sorghum plants. BADH1 and BADH15 mRNA were both
induced by water deficit and their expression coincided with the observed
glycine betaine accumulation. During the course of 17 d, the leaf water
potential in stressed sorghum plants reached -2.3 MPa. In response to water
deficit, glycine betaine levels increased 26-fold and proline levels
increased 108-fold. In severely stressed plants, proline accounted for
>60% of the total free amino acid pool. Accumulation of these compatible
solutes significantly contributed to osmotic potential and allowed a
maximal osmotic adjustment of 0.405 MPa.