Induction of a C4-like mechanism of CO2 fixation in Egeria densa, a submersed aquatic species

CASATI, PAULA; LARA, MARIA V.; ANDREO, CARLOS S.

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Año: 2000 vol. 123 p. 1611 - 1623

0032-0889

The expression of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme (NADP-ME) in Egeria densa leaveswas studied under low temperature and light (LTL) following incubation under high temperature and light (HTL),conditions previously shown to induce high and low CO2 compensation points, respectively. Transfer from LTL to HTLconditions induced increases in the activities and amounts of both enzymes. One NADP-ME isoform was observed ininduced and uninduced samples. Two isoforms of PEPC were expressed, with the lower Mr isoform being induced by HTL.NADP-ME showed properties similar to those of the isoform in C3 species. The inducible PEPC isoform has a low Km forboth substrates. PEPC kinetic and regulatory properties (Vmax and Km for phosphoenolpyruvate, and I50 for l-malate) aredifferent in samples taken in the dark from those in the light, indicating that some modification of PEPC may be occurringduring the day. Finally, abscisic acid induced the expression of PEPC and NADP-ME in a manner similar to temperatureinduction, except that the activities of both PEPC isoforms were increased. A different signaling system may exist in thisspecies in response to high temperature or abscisic acid, both of which induce changes in photosynthetic metabolism.