An isozyme of betaine aldehyde dehydrogenase in barley

Isolating the promoter of a stress-induced gene encoding betaine aldehyde dehydrogenase from the halophyte Atriplex centralasiatica Iljin

The betaine aldehyde dehydrogenase (AcBADH) gene of the halophyte Atriplex centralasiatica Iljin is induced by drought, salinity, cold stress and abscisic acid, in parallel with an increase in betaine level. In order to study the molecular basis of its expression and to obtain an effective stress-induced promoter, the 5' flanking region of betaine aldehyde dehydrogenase gene (about 1.2 kb) was isolated from the halophyte A. centralasiatica Iljin by screening the genomic library. The transcription start site, which localized at 84 bases upstream of the start ATG, was determined by primer extension and 5'-RACE method. To investigate the molecular mechanism of the stress-induced gene regulation, the AcBADH promoter-beta-glucuronidase chimeric gene constructs containing six deletions were introduced into tobacco by Agrobacterium-mediated transformation. The AcBADH 5'-flanking region, a promoter strongly induced by salt stress, contains two salt-responsive enhancer regions localized between -1115 and -890, -462 and -230 and one silencer region between -890 and -641.

Inducers of glycinebetaine synthesis in barley

Glycinebetaine is an osmoprotectant accumulated by barley (Hordeum vulgare) plants in response to high levels of NaCl, drought, and cold stress. Using barley seedlings in hydroponic culture, we characterized additional inducers of glycinebetaine accumulation. These included other inorganic salts (KCl, MgCl(2), LiCl, and Na(2)SO(4)), oxidants (H(2)O(2) and cumene hydroperoxide), and organic compounds (abscisic acid, polymixin B, n-butanol, salicylic acid, and aspirin). Stress symptoms brought on by high NaCl and other inducers, and not necessarily correlated with glycinebetaine accumulation, include wilting, loss of chlorophyll, and increase in thiobarbituric acid reacting substances. For NaCl, Ca(2+) ions at 10 to 20 mM decrease these stress symptoms without diminishing, or even increasing, glycinebetaine induction. Abscisic acid induces glycinebetaine accumulation without causing any of the stress symptoms. NaCl, KCl, and H(2)O(2) (but not other inducers) induce glycinebetaine at concentrations below those needed for the other stress symptoms. Mg(2+) at 10 to 20 mM induces both stress symptoms and glycinebetaine, but only at low (0.2 mM) Ca(2+). Although illumination is needed for optimal induction, a significant increase in the leaf glycinebetaine level is found in complete darkness, also.