NADP-MALIC ENZYME 1 affects germination after seed storage in Arabidopsis thaliana.

Aging decreases the quality of seeds and results in agricultural and economic losses. The damage that occurs at the biochemical level can alter the seed physiological status. Although loss of viability has been investigated frequently, little information exist on the molecular and biochemical factors involved in seed deterioration and loss of viability. Oxidative stress has been implicated as a major contributor to seed deterioration and several pathways are involved in protection against this. In this study, we show that seeds of Arabidopsis thaliana lacking a functional NADP-MALIC ENZYME 1 (NADP-ME1) have reduced seed viability relative to wild type. Seeds of the nadp-me1 loss-of-function mutant display higher levels of protein carbonylation than wild type. NADP-ME1 catalyses the oxidative decarboxylation of malate to pyruvate with the simultaneous production of CO2 and NADPH. Upon seed imbibition malate and amino acids accumulate in embryos of aged seeds of the NADP-ME1 loss-of-function mutant compared to wild type. NADP-ME1 expression is increased in imbibed aged- as compared to non-aged seeds. NADP-ME1 activity at testa rupture promotes normal germination of aged seeds. In seedlings of aged seeds NADP-ME1 is specifically active in the root meristematic zone. We propose that NADP-ME1 activity is required for protecting seeds against oxidation during seed dry storage.