Abstract
NADP –ME is the key enzyme for decarboxylation reactions in C4 CO2 concentration pathways. So, Amaranthus viridis has been evaluated with regards to photosynthetic NADP-malic enzyme for its response under light and darkness. Illumination (1000–1200 µEm-2s-1) for 40 minutes under 2 mM bicarbonate (HCO3-) sensitivity increased activity by 1.97 & 3.77-fold over darkness under 4.0 mM and 0.01 mM malate respectively. Limiting (0.01 mM) and saturated (4.0 mM) malate concentration had significant changes in enzyme activities. The different kinetic parameters indicated had the feedback inhibition under illumination. The activity with the inducer (citrate and succinate) and inhibitor (pyruvate and oxalate) was significant with substrate concentrations. Dithiol had reduced the activity by inhibition of the diminishing effect of light activation treatment. Therefore, NADP-ME is stringently regulated by redox changes with illumination as a key factor. Moreover, the pattern of polymorphic gene expression may be supportive in molecular modulation under light/darkness. This study may support the role of NADP-ME as a biomarker for C4 weed species under oxidative stress through light/darkness.
Highlights
For the anaplerotic metabolism in plants, a few oxidative decarboxylation reactions are important
The enzymatic properties of NADP-malic enzyme (NADP-ME) were evaluated under conditions of light and darkness
The results revealed the role of activators were more inducing at 0.01 mM than 4.0 mM of malate concentration
Summary
For the anaplerotic metabolism in plants, a few oxidative decarboxylation reactions are important. The NADP-malic enzyme (NADP-ME) belongs to a member of NADP oxidoreductase (EC 1.1.1.40) causing decarboxylation of oxaloacetic acid (OAA) as well as oxidation of malate (substrate). The product is pyruvate, reduced NADP (NADPH+H+) with the simultaneous release of CO2. The chief function of NADP-ME is in photosynthetic C4-CO2 concentration mechanism [1]. The reduced carbon with different forms is required to donate the carbon residues for the synthesis of biomolecules [2]. In C4 plants like Zea mays L., Amaranthus viridis L. and Saccharum officinarum L. NADP-ME is exclusively bound in bundle sheath chloroplast. In CAM plants, it is localised in the cytosol [3]. Few nonphotosynthetic forms of NADP-ME are important with varying polymorphisms in different plant tissues
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