Arabidopsis thaliana expressing high levels of maize NADP-malic enzyme displays modified photosynthetic parameters

MARIANA SAIGO; ROODRIGO D´ANDREA; VERÓNICA MAURINO; MARÍA F. DRINCOVICH; CARLOS ANDREO

Iguazú, Argenina

Congreso; Sociedad Argentina de Investigación en Bioquímica y Biología Molecular XL Reunión Anual; 2004

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Arabidopsis thaliana (Columbia-0 ecotype) was transformed with a vector containing the maize chloroplastic NADP-malic enzyme (NADP-ME) cDNA under the control of 35SCaMV promoter. This enzyme catalyzes the oxidative decarboxylation of malate, generating pyruvate, CO2 and NADPH. Homozygous plants for the transgene were selected and the level of ME expression was examined in several lines. The line with the highest expression level showed a 30-fold increase in NADP-ME activity. Western blots, as well as non denaturing electrophoresis stained for ME activity, confirmed the presence of 62 kDa ME in this plant. Plants grown under normal light intensity showed no major morphological differences compared to the wild type line (WT). However, chlorophyll content as well as photosynthetic performance indicators like CO2 assimilation, Fv/Fm and FPSII were significantly lower for transgenic lines. These results suggest that the presence of a highly active NADP-ME in chloroplasts of A thaliana, could have important effects on the reductive power balance of this organelle, diminishing the efficiency of the overall photosynthetic process. In this way, the mechanisms that protect the photosynthetic machinery, normally triggered by a raise in NADPH level, are exceeded in the transgenic line leading to photoinhibition. The transgenic plants obtained in the present work will be use as a tool to better understand the regulation of plastid redox metabolism.