Abstract:

Drought and salinity are the most important abiotic stresses affecting the normal growth and development of plants. One of the fundamental physiological mechanisms of higher plant to cope with environmental stresses is osmotic adjustment, and glycine betaine is one of the most important osmolytes. Glycine betaine is regarded as one of the most promising osmolytes because it possesses simple biosynthesis pathways, non-toxic to cells, and non-osmotic functions in stabilizing enzyme activities and membrane structures.
In order to establish a glycine betaine biosynthetic pathway in glycine betaine-deficient crop plants through genetic engineering, which can enhance drought and salinity tolerances of crop plants, a betaine aldehyde dehydrogenase (BADH) gene which is the key gene for glycine betaine synthesis was isolated from spinach (Spinacia oleracea L.) (GenBank accession No.AY156694). The expression plasmid pBIBB was constructed by fusing the BADH gene with the constitutive promoter CaMV 35S. The transgenic tobacco plants were obtained by transformation of the expression plasmid pBIBB and mediation of Agrobacterium tumefaciens. PCR, Southern and Northern blot analyses indicated that the BADH gene has been integrated into genome of tobacco, transcribed and expressed in transgenic tobacco plants. The testing of BADH activity of transgenic plant leaves showed that the BADH specific activity ranged from 0.1 to 1.0 U mg^-1, while it was not detectable in the control plants. The growth of the transgenic tobacco plants was normal and better than the untransformed plants under salt and polyethylene glycol (PEG) stresses. Plant height and fresh weight per plant of transgenic plant lines had a significant increase compared with those of untransformed control plants. This result proves that the BADH gene can express accurately in the exogenous transgenic plants and can be used in genetic engineering for plant drought and salt resistances.

Key words: Betaine aldehyde dehydrogenase gene, Tobacco, Transformation, Drought resistance, Salt tolerance