TRANSGENICALLY PRODUCED GLYCINEBETAINE PROTECTS RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE FROM INACTIVATION IN SYNECHOCOCCUS SP. PCC7942 UNDER SALT STRESS/

Synechococcus sp. PCC7942 cells transformed with Escherichia coli bet genes accumulated glycinebetaine (to about 80 mM) and acquired an incr eased tolerance to salt stress. Ribulose 1,5-bisphosphate carboxylase activity in the extract from control cells was found to decrease more rapidly than that of either PSI or PSII under salt stress. We examined levels of the transcript, the protein and the enzyme activity of ribu lose 1,5-bisphosphate carboxylase to determine at which level the enzy me is affected at the early stages of salt stress. The levels of rbcL mRNA in both control and bet-containing cells increased around two-fol d under salt stress compared to those under non-stress. Bet-containing cells showed slightly reduced levels of rbcL mRNA under both non-stre ss and salt stress compared to control cells. The protein levels of th e enzyme in the control and bet-containing cells were almost the same and were little changed by salt stress, On the other hand, salt stress drastically decreased the enzyme activity in control cells, but not a s much in the bet-containing cells. Interestingly the lowered enzyme a ctivity in extracts from control cells grown under salt stress, as wel l as acid-denatured enzyme, was partially reactivated by glycinebetain e.