RT Journal Article
SR Electronic
T1 Deriving C<sub>4</sub> photosynthesis parameters by fitting intensive A/C<sub>i</sub> curves
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 153072
DO 10.1101/153072
A1 Haoran Zhou
A1 Erol Akçay
A1 Brent R. Helliker
YR 2018
UL http://biorxiv.org/content/early/2018/10/13/153072.abstract
AB Measurements of photosynthetic assimilation rate as a function of intercellular CO2 (A/Ci curves) are widely used to estimate photosynthetic parameters for C3 species, yet few parameters have been reported for C4 plants, because of a lack of estimation methods. Here, we extend the framework of widely-used estimation methods for C3 plants to build estimation tools by exclusively fitting intensive A/Ci curves (6-8 more sampling points) for C4 using three versions of photosynthesis models with different assumptions about carbonic anhydrase processes and ATP distribution. We use simulation-analysis, out-of-sample tests, existing in vitro measurements and chlorophyll-fluorescence-measurements to validate the new estimation methods. Of the five/six photosynthetic parameters obtained, sensitivity analyses show that maximal-Rubisco-carboxylation-rate, electron-transport-rate, maximal-PEP-carboxylation-rate and carbonic-anhydrase were robust to variation in the input parameters, while day-respiration and mesophyll-conductance varied. Our method provides a way to estimate carbonic anhydrase activity, a new parameter, from A/Ci curves, yet also shows that models that do not explicitly consider carbonic anhydrase yield approximate results. The two photosynthesis models, differing in whether ATP could freely transport between RuBP and PEP regeneration processes yielded consistent results under high light, but they may diverge under low light intensities. Modeling results show selection for Rubisco of low specificity and high catalytic rate, low leakage of bundle sheath and high PEPC affinity, which may further increase C4 efficiency.Abbreviationsalight absorptance of leafAcRubisco carboxylation assimilation rateAEERuBP carboxylation and PEPc carboxylation limitation assimilationAETRuBP regeneration and PEP carboxylation limitation assimilationAggross CO2 assimilation rate per unit leaf areaAjRuBP regeneration assimilation rateAnnet CO2 assimilation rate per unit leaf areaATERuBP carboxylation and PEPc regeneration limitation assimilationATTRuBP regeneration and PEPc regeneration limitation assimilationαthe fraction of O2 evolution occurring in the bundle sheathcscaling constant for temperature dependence for parametersCaLLower boundary CO2 under which assimilation is limited by RuBP carboxylation and PEPc carboxylationCaHHigher boundary CO2 above which assimilation is limited by RuBP regeneration and PEPc regenerationCbsbundle sheath CO2 concentrationCiintercellular CO2 concentrationCmmesophyll CO2 concentrationΔHaenergy of activation for temperature dependence for parametersΔHdenergy of deactivation for temperature dependence for parametersΔSentropy for temperature dependence for parametersϕPSIIquantum yieldγ*(25)the specificity of Rubisco at 25°Cgbsbundle sheath conductance for CO2gbsobundle sheath conductance for O2gmmesophyll conductance for CO2Ilight intensityJmax(25)maximum rate of electron transport at 25°CKc(25)Michaelis-Menten constant of Rubisco activity for CO2 at 25°CKo(25)Michaelis-Menten constants of Rubisco activity for O2Kp(25)Michaelis-Menten constants of PEP carboxylation for CO2ObsO2 concentration in the bundle sheath cellsQ10 for Kptemperature sensitivity parameter for KpRthe molar gas constantRddaytime respirationRdbsdaytime respiration in bundle sheath cellsRdmdaytime respiration in mesophyll cellsRubiscoribulose-1,5-bisphosphate carboxylase/oxygenaseRuBPribulose-1,5-bisphosphateTkleaf absolute temperatureVcvelocity of Rubisco carboxylationVcmax(25)maximal velocity of Rubisco carboxylation at 25°CVpPEP carboxylationVpcPEPc reaction rateVpmax(25)maximal PEP carboxylation rate at 25°CVprPEP regeneration ratexthe maximal ratio of total electron transport could be used for PEP carboxylation.