Tobacco (Nicotiana tabacum L.) has been transformed to accumulate different compatible solutes (proline, fructans, or glycine betaine) in order to improve its tolerance to abiotic stress. Photosynthetic activity of wild Type (wt) and transformed tobacco plants before and after freezing stress was studied by measuring chlorophyll (Chl) fluorescence. The JIP test of Chl fluorescence induction was used to analyze in details the functional activity of photosystem 2. No significant differences were found among wild Type and transgenic plants after 12 h of freezing. Both plant Types maintained the same values of the measured parameters [FV/FM, PI(CSM), ABS/RC, TR0/RC, ET/RC] after recovery of stress. The studied Chl fluorescence parameters decreased only for the wild Type plants, stressed for 24 h at -2 °C. The strong inhibition of photosynthetic reactions in the wt plant after 24 h of freezing could not be restored. The evaluated parameters of transgenic plants did not change significantly after 24 h at -2 °C and successfully survived freezing stress. and D. Parvanova ... [et al.].