REDUCTION OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE EFFICIENCY BY THE PRESENCE OF SUCROSE DURING THE TISSUE-CULTURE OF STRAWBERRY PLANTLETS

In order to identify the physiological and biochemical events leading to the negative effects of the presence of sucrose in culture medium o n the photosynthetic capacity of plantlets cultivated in vitro, time c ourse changes in photosynthesis, metabolite pool sizes, and ribulose-1 ,5-bisphosphate carboxylase (EC 4.1.1.39) activity were investigated i n strawberry (Fragaria x ananassa. Duch. cv. Kent) plantlets following their transfer to medium with or without sucrose. When the plantlets grown in medium without sucrose were transferred to a similar medium w ith 30 g liter(-1) sucrose, their net photosynthesis decreased and the ir level of phosphorylated compounds increased with time. In addition, initial catalytic turnover, total catalytic turnover, and the activat ion state of ribulose-1,5-bisphosphate carboxylase decreased in these plantlets. Conversely, when the plantlets grown in medium with 30 g li ter(-1) sucrose were transferred to a similar medium without sucrose, their net photosynthesis slowly increased with time and their level of phosphorylated compounds slowly decreased. A slow increase with time of initial catalytic turnover, total catalytic turnover, and the activ ation state of ribulose-1,5-bisphosphate carboxylase was also observed in these plantlets. The results of the present paper suggest that the reduced photosynthetic capacity of strawberry plantlets cultivated in vitro in the presence of sucrose is the consequence of a reduction in the efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase due to its deactivation and the possible presence of putative inhibitors of carboxylation sites.