Ribulose-1,5-bis-phosphate carboxylase activity in altitudinal populations of Espeletia schultzii Wedd

The ribulose-1,5-bis-phosphate (RBPC) ¹⁴CO₂ fixation rate was measured at four different temperatures, 5°, 15°, 25° and 35° C, in three populations of Espeletia schultzii at different altitudes, 3100, 3550 and 4200 ma.s.l. The fixation rate increased with temperature increase in the populations studied. The population at 4200 m showed the higher rate at any temperature, followed by those at 3550 and 3100 m. The Km(CO₂) increased with temperature increase, but the values were similar among populations. The V _max values increased with temperature and were higher for the 4200-m population. These results suggest that the RBPC enzyme is more activated in the highland population and that the enzyme kinetics are not similar among populations.