Specificity factor of Rubisco: Estimation in intact leaves by carboxylation at different CO 2/O 2 ratios

Abstract

The specificity factor of Rubisco (S f) was estimated in intact leaves from the carboxylation of ribulose-1,5-bisphosphate (RuBP) at various CO 2/O 2 ratios. As oxygenation is calculated by the difference of the 14CO 2 uptake by RuBP in the absence and presence of oxygen, it is important to choose the optimum CO 2/O 2 ratios. At high CO 2 concentration (1,000 cm 3 m -3 and higher) oxygenation consumes less than 50% RuBP but the difference of concentrations of CO 2 at cell walls (C w) and at the carboxylation centers (C c) is 2-5% and the influence of mesophyll resistance (r md) is of minor importance. To accumulate large endogenous pool of RuBP, the leaves were preilluminated in the CO 2- and O 2-free gas environments for 8 to 10 s. Thereafter the light was switched off and the leaves were flushed with the gas containing different concentrations of 14CO 2 and O 2. The specificity factor of Rubisco was calculated from the amount of the tracer taken up under different 14CO 2/O 2 ratios by the exhaustion of the RuBP pool. Application of 14CO 2 allowed us to discriminate between the CO 2 uptake and the concurrent respiratory CO 2 release which proceeded at the expense of unlabelled intermediates. © 2012 Springer Science+Business Media B.V.