High level of NADP-malic enzyme in plastids reduces prolonged darkness tolerance in A. thaliana

SAIGO M,; FAHNENSTICH, H.; M, N.; DRINCOVICH MF,; CARLOS SANTIAGO ANDREO; FLUGGE, U.; MAURINO VG,

Rosario

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular, SAIB.; 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 (MEm plants). 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 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, these metabolites are consumed faster than in the wild-type in prolonged darkness and, as a consequence, MEm plants enter senescence more rapidly