Improved tolerance to salinity and low temperature in transgenic tobacco producing glycine betaine

Glycine betaine is an osmoprotectant found in many organisms, including bac teria and higher plants. The bacterium Escherichia coli produces glycine be taine by a two-step pathway where choline dehydrogenase (CDH), encoded by b etA, oxidizes choline to betaine aldehyde which is further oxidized to glyc ine betaine by the same enzyme, The second step, conversion of betaine alde hyde into glycine betaine, can also be performed by the second enzyme in th e pathway, betaine aldehyde dehydrogenase (BADH), encoded by betB. Transfor mation of tobacco (Nicotiana tabacum), a species not accumulating glycine b etaine, with the E. coli genes for glycine betaine biosynthesis, resulted i n transgenic plants accumulating glycine betaine. Plants producing CDH were found to accumulate glycine betaine as did F-1 progeny from crosses betwee n CDH- and BADH-producing lines. Plants producing both CDH and BADH general ly accumulated higher amounts of glycine betaine than plants producing CDH alone, as determined by H-1 NMR analysis, Transgenic tobacco lines accumula ting glycine betaine exhibited increased tolerance to salt stress as measur ed by biomass production of greenhouse-grown intact plants. Furthermore, ex periments conducted with leaf discs from glycine betaine-accumulating plant s indicated enhanced recovery from photoinhibition caused by high light and salt stress as well as improved tolerance to photoinhibition under low tem perature conditions. In conclusion, introduction of glycine betaine product ion into tobacco is associated with increased stress tolerance probably par tly due to improved protection of the photosynthetic apparatus.