THE ACTION IN-VIVO OF GLYCINE BETAINE IN ENHANCEMENT OF TOLERANCE OF SYNECHOCOCCUS SP STRAIN PCC-7942 TO LOW-TEMPERATURE

The cyanobacterium Synechococcus sp. strain PCC 7942 was transformed w ith the codA gene for choline oxidase from Arthrobacter globiformis un der the control of a constitutive promoter. This transformation allowe d the cyanobacterial cells to accumulate glycine betaine at 60 to 80 m M in the cytoplasm, The transformed cells could grow at 20 degrees C, the temperature at which the growth of control cells was markedly supp ressed, Photosynthesis of the transformed cells at 20 degrees C was mo re tolerant to light than that of the control cells, This was caused b y the enhanced ability of the photosynthetic machinery in the transfor med cells to recover from low-temperature photoinhibition. In darkness , photosynthesis of the transformed cells was more tolerant to low tem perature such as 0 to 10 degrees C than that of the control cells, In parallel with the improvement in the ability of the transformed cells to tolerate low temperature, the lipid phase transition of plasma memb ranes from the liquid-crystalline state to the gel state shifted towar d lower temperatures, although the level of unsaturation of the membra ne lipids was unaffected by the transformation. These findings suggest that glycine betaine enhances the tolerance of photosynthesis to low temperature.