An intermediate form of NADP-malic enzyme from the C3C4 intermediate species Flaveria floridana

NADP-malic enzyme (NADP-ME) characterization and compartmentation between the mesophyll and bundle sheath cells was studied in the C-3-C-4 intermediate species of Flaveria floridana. Although three immunoreactive bands were found in crude leaf extracts,: only one isoform was purified to homogeneity, probably:due to the low specific activity of the other forms and/or differential susceptibility to proteases' action. The purified enzyme showed intermediate kinetic features between those from C-3 and C-4 plants, although the molecular mass was more like that for the-enzyme found in C-4 plants. The amino terminal sequence of the purified enzyme, despite some changes, was similar to the deduced protein sequence obtained from different Flaveria NADP-ME cDNA clones although the sequence did not follow the proposed cleavage site of the transient peptide. Localization studies df certain photosynthetic enzymes between the mesophyll and bundle sheath cells indicated that phosphoenolpyruvate carboxylase (PEPC) as well as photosynthetic isoforms of NADP-ME are partially compartmentalized as in C-4 plants, while RuBisCO is present in both types of cells. In this way, the intermediate features of the C-3-C-4 species F. floridana in relation to C-4 plants may be due not only to the lack of compartmentation of RuBisCO, but also to the presence of C-4 enzymes with kinetic intermediate features. It is suggested that during the evolution of C-4 photosynthesis not only changes in the level of expression and compartmentation of key photosynthetic enzymes have occurred, but also the development of new photosynthetic enzymes with C-4-like kinetic features. (C) 1999 Elsevier Science Ireland Ltd; All rights reserved.