Characterization of Phosphoenolpyruvate carboxylase in species of family Chenopodiaceae having single-cell C4 photosynthesis

LARA, MARIA V.; CHOUNG, SIMON D.X.; ANDREO, CARLOS S.; EDWARDS, GERALD E.

Pinamar

Congreso; XLI Reunión Anual de SAIB, X Congreso PABMB, XX Reunión Anual SAN; 2005

Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB)

Recently, the paradigm that Kranz anatomy is required for functioning of C4 photosynthesis in terrestrial plants has been broken. It was shown that Bienertia sinuspersici and Borsczowia aralocaspica (Chenopodiaceae) perform photosynthesis through unique single cell systems and they have C4/CAM carbon isotope composition. Phosphoenolpyruvate carboxylase (PEPC) catalyses the first committed step of C4 photosynthesis. Although this ubiquitous enzyme is also present in low levels in C3 species, the form involved in the C4 cycle has distinct kinetic and regulatory properties.  The goal of this work was to characterize the PEPC present in both single-cell species and to compare with those present in other Chenopodiaceae C3 and C4 species. In both species, PEPC is a tetramer of four subunits each with a molecular mass of about 100 kDa. In addition, native isoelectrofocusing and western blot using specific antibodies shown that the enzyme is phosphorylated during the day, as occurs in Kranz C4-type PEPCs. This regulatory phosphorylation is responsible for changes in the kinetic parameters and sensitivity to  malate during the day and night periods in agreement with a C4-type PEPC. Thus, analysis of the kinetic and regulatory properties of PEPC in B. sinusperisci and B. aralocaspica supports the conclusion that C4 photosynthesis is taking place in these species.