tThe submersed species Egeria densa possesses an inducible C4-like photosynthetic system after expo-sure to low CO2concentrations. Four full-length and one partial cDNAs encoding plant-type PEPC wereidentified, named EdPEPC1-5; and one partial cDNA encoding bacterial-type PEPC was identified. Noneof the C4-signature amino acid substitutions which were found in C4-type PEPC isoforms of terrestrial C4plants were found in EdPEPCs. Real-time qPCR experiments indicated that in the high CO2concentration,all these isoforms were expressed at low levels in leaves and stems. However after exposure to low CO2concentration, EdPEPC1 was significantly up-expressed in the stems and leaves, and may thus correspondto the C4-form. The results of enzyme assays and western blotting showed increases in the activities andamount of PEPC in the leaves and stems after incubation at low [CO2]. EdPEPC1, gene that responds to low[CO2], might be involved in the emergence of the inducible C4-like mechanism in E. densa. For the firsttime in submersed plants, the results suggested that stems as well as leaves were likely to be involved inthe C4-like mechanism.
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