High levels of NADP-Malic Enzyme in plastids reduces long darkness tolerance in A. thaliana

MARIANA SAIGO; HOLGER FAHNENSTICH; MICHAELA NIESSEN; MARÍA FABIANA DRINCOVICH; CARLOS ANDREO; ULF-INGO FLÜGGE; VERÓNICA MAURINO

Rosario, Argentina

Congreso; Sociedad Argentina de Investigación en Bioquímica y Biología molecular XLII Reunión anual; 2006

Sociedad Argentina de Investigación en Bioquímica y Biología molecular

The full-length cDNA encoding maize C4 NADP-malic enzyme was expressed under the control of the CaMV35S promoter in Arabidopsis thaliana. An increase in the plastidic NADP-ME activity led to a green pale phenotype in plants growing in short days and low to moderate irradiance. In these conditions, MEm plants have a decreased fresh weight/area ratio and thinner leaf sections. Measurements of chlorophyll content, chlorophyll fluorescence and CO2 assimilation indicated that the expression of highly active NADP-ME altered photosynthetic metabolism. This phenotype can be reverted by transferring the plants under high light. Moreover, all these features are absent in plants growing in long-day conditions. Metabolite levels of rosettes from transgenic plants indicated that plants grown in both photoperiods have a disturbed metabolic profile. Additionally, dark-induced senescence of intact plants progressed more rapidly in MEm plants compared to the wild type. While four week-old wild-type plants became pale green five days after the onset of darkness, MEm plants showed this characteristic already after two days with severe yellowing after three days in darkness. Since MEm plants accumulate lower levels of intermediates used as respiratory energy, in prolonged darkness these metabolites are consumed faster than in the wild-type and, as a consequence, MEm plants enter senescence more rapidly.