Info

Days 5 -10

Days 10-15

Days 15-20

Days 20-25

NaCI-free betl/betl 289

Betl/Betl 260

With NaCI betl/betl 207

Betl/Betl 218

268 233 175

260 224 184

168 82 84

190 121 121

NaCI-free betl/betl 289

Betl/Betl 260

With NaCI betl/betl 207

Betl/Betl 218

268 233 175

260 224 184

168 82 84

190 121 121

Since glycine betaine has long been thought to be an efficient osmolyte, efforts have been made to develop lines of crop plants which produce large amounts of this compound upon salt stress by classical breeding. This has been achieved with maize: The sister lines Betl/Betl are glycine betaine producers, the homozygotic betl/betl are glycine betaine-deficient.

Table 1.6.5 A shows the enhanced glycine betaine accumulation of the Betl/Betl maize, particularly in relation to salt stress; the contents of Na+ and particularly Cl~ are also distinctly higher on salt. The decrease in the concentration of carbohydrates in the expressed sap of the leaves (which is much higher than that of glycine betaine) correlates with the increase in the glycine betaine concentration. Presumably some of the carbohydrate carbon was used for the synthesis of the physiologically superior osmolyte glycine betaine.

Salt inhibits growth, but in this regard Betl/ Betl is seen to suffer considerably less (i.e. it exhibits better leaf growth) than does betl/betl under salt stress (Table 1.6.5 B). The less impaired growth correlates with an at least partial maintenance of cell turgor under salt stress (0.06 MPa in betl/betl and 0.2 MPa in Betl/Betl; Saneoka et al. 1995).

Glycine betaine accumulates particularly in young tissues, where it competes with NaCI and somewhat reduces the content of the salt. There is, however, no indication that glycine betaine is transported within the plant. It evidently is stored at the site at which it is produced from choline (Nakamura et al. 1996).

Because glycine betaine ameliorates stress and plants are evidently unable to metabolise this compound and thus accumulate it, attempts have long since been made to transform crop plants lacking glycine betaine with the key gene encoding choline monooxygenase (CMO), which is required for glycine betaine synthesis. This is difficult in that this enzyme contains a Rieske-[2Fe-2S]-centre. Since glycine betaine synthesis takes place in the chloroplast, it must also be taken into consideration that the recombinant protein (CMO) would have to be transported into the chloroplasts. Such a transformation has recently been successful with tobacco (Nuccio et al. 1998). Accumulation of glycine betaine was, however, only weakly pronounced, because tobacco produces choline - the starting compound for glycine betaine synthesis - only in very small amounts (McNeil et al. 1999).

What Is the Special Protective Effect of QACs?

Transformation of the cyanobacterium Synecho-coccus with an E. coli glycine betaine synthesis cassette consisting of choline monooxygenase, betaine aldehyde dehydrogenase, a choline

Days of culture in NaCI

Days of culture in NaCI

| Fig. 1.6.14. Growth of wild-type and transformed Synechococcus cells under salinity stress. The cells were grown in choline-containing medium which was supplemented with NaCI at the indicated concentrations after 2 days (time 0 in the graph). The transformants contained the glycine betaine cassette. The glycine betaine concentration in the cells stressed with the higher NaCI concentrations was about 15 times higher than in the unstressed cells. (After Nomura et al. 1995)

Days of culture in NaCI

Days of culture in NaCI

Days of culture in NaCI

| Fig. 1.6.14. Growth of wild-type and transformed Synechococcus cells under salinity stress. The cells were grown in choline-containing medium which was supplemented with NaCI at the indicated concentrations after 2 days (time 0 in the graph). The transformants contained the glycine betaine cassette. The glycine betaine concentration in the cells stressed with the higher NaCI concentrations was about 15 times higher than in the unstressed cells. (After Nomura et al. 1995)

| Table 1.6.6. Effect of salinity on the photosynthetic electron transport of glycine betaine-accumulating Synechococcus cells (transformants) and non-accumulating Synechococcus (control) cells. DADH2 reduced 2,3,5,6-tetramethylphenylenedia-mine; MV methyl viologen; PBQ phenyl-1,4-benzoquinone. The reaction of photosystem I consumes (reduces) 02 and that of photosystem II produces 02. (After Nomura et al. 1995)

| Table 1.6.6. Effect of salinity on the photosynthetic electron transport of glycine betaine-accumulating Synechococcus cells (transformants) and non-accumulating Synechococcus (control) cells. DADH2 reduced 2,3,5,6-tetramethylphenylenedia-mine; MV methyl viologen; PBQ phenyl-1,4-benzoquinone. The reaction of photosystem I consumes (reduces) 02 and that of photosystem II produces 02. (After Nomura et al. 1995)

Reaction

02 production or uptake (|.imol/mg ChjaB

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