
%0 Journal Article
%A Oja, VM 
%A Rasulov, BH 
%A Laisk, AH 
%T An Analysis of the Temperature Dependence of Photosynthesis Considering the Kinetics of RuP<sub>2</sub> Carboxylase and the Pool of RuP<sub>2</sub> in Intact Leaves
%J Functional Plant Biology
%D 1988/12/01
%V 15
%N 6
%P 737-748
%K 
%R https://doi.org/10.1071/PP9880737
%U https://www.publish.csiro.au/paper/PP9880737 
%X Sunflower and cotton plants were grown in growth boxes at 460 µmol m-2 s-1. The mesophyll conductance in N2, the assimilatory charge (post-illumination CO2 uptake) and the CO2 capacity (the solubility of CO2 + HCO3- + CO32-) were measured at different temperatures. The mesophyll conductance had its maximum at 29-30&#176;C in sunflower leaves and rapidly declined at higher and lower temperatures. In cotton, the maximum occurred at a somewhat higher temperature. The assimilatory charge changed in parallel with the mesophyll conductance. When the assimilatory charge was measured after a short exposure to CO2-free N2, it remained constant at lower temperatures and declined only at superoptimal temperatures. As the assimilatory charge reflects the RuP2 pool in the leaf, the temperature dependence of the mesophyll conductance at a constant assimilatory charge reveals the actual activation energy of the CO2 binding reaction of carboxylase (together with the CO2 transport conductance in the liquid phase of mesophyll cells) which was 29 kJ mol-¹ for both species.    At superoptimal temperatures, the primary cause for the reversible decrease of photosynthesis was a decrease in the assimilatory charge (RuP2 pool). The decrease cannot be caused by an inadequate rate of RuP2 resynthesis but is, presumably, the result of either too rapid drainage of triosephosphates to the cytosol from chloroplasts or de-energisation of thylakoids at high temperatures. 
