Phosphoenolpyruvate Carboxylase (PEPC; EC: 4.1.1.31) and Ribulose 1.5-bisphosphate Carboxylase/Oxygenase (RubisCO; EC: 4.1.1.39) enzyme specific activities were measured during the in vitro development of coconut (Cocos nucifera L.) zygotic mature embryos into plantlets and compared with those of palms produced by conventional seed germination. At the time of initiation of germination, high PEPC and low RubisCO activities were measured in both cultured and conventionally germinated embryos, thus indicating an anaplerotic C02 fixation. During both in vitro and in planta development, RubisCO progressively took over and became the main route for inorganic carbon fixation. The in vitro-grown coconut plantlets showed a faster decrease in their PEPC/RubisCO ratio than the seedlings, suggesting that an earlier transition from a heterotrophic to an autotrophic mode on carbon fixation takes place in the in vitro-denved material. Just before acclimatization, the RubisCO activity in in vitro-derived plantlets (2.83 pmol C02h-1mg-1 TSP) was lower than that in seedlings (6.98 pmol C02h-1 mg-1 TSP ) for the same age. Nevertheless, after acclimatization, RubisCO activities were comparable in both in vitro and in planta germinated materiel.