Evolution of C4 photosynthesis in Flaveria species. Isoforms of NADP-malic enzyme

MARIA FABIANA DRINCOVICH; CASATI, P; ANDREO, CS; FRANCESCHI, VR; EDWARDS, GE; KU, MSB

PLANT PHYSIOLOGY.

Lugar: ASPP; Año: 1998 vol. 117 p. 733 - 744

0032-0889

NADP-malic enzyme (NADP-ME, EC 1.1.1.40), a key enzyme in C4 photosynthesis, provides CO2 to the bundle sheath chloroplasts where it is fixed by Rubisco. We characterized the isoform pattern of NADP-ME in different photosynthetic species of Flaveria (C3, C3-C4 intermediate, C4-like, C4) based on sucrose density gradient centrifugation and isoelectric focusing of the native protein, western blot analysis of the denatured protein, and in situ immunolocalization with antibody against the 62 kD C4 isoform of maize. A 72 kD isoform, present to varying degrees in all species examined, is predominant in leaves of C3 Flaveria and is also present in stem and root tissue.  By immunolabeling, NADP-ME was found to be mostly localized in the upper palisade mesophyll chloroplasts of C3 photosynthetic tissue.  Two other isoforms of the enzyme, 62 and 64 kD, occur in leaves of certain intermediates having C4 cycle activity.  The 62 kD isoform, which is a predominant highly active form in the C4 species, is localized in bundle sheath chloroplasts.  Among Flaveria species there is a 72 kD constitutive form, a 64 kD form which may have appeared during evolution of C4 metabolism, and a 62 kD form which is necessary for the complete functioning of C4 photosynthesis