Physiological characterization of NADP-malic enzyme activity under 2,4-D toxicity in an aquatic fern, Azolla pinnata R.Br.

This work proposes NADP-ME activity as bio-indices for herbicidal sensitivity in Azolla pinnata R.Br. under 2,4-D toxicity. Azolla fronds were illuminated under saturated photosynthetic flux and bicarbonate induction. There was significant variation in the NADP-ME activity under light and dark conditions. This increased more when varying concentrations of 2,4-D were used for the up regulation of enzyme activity especially under illumination. There was evident modulation through activators (citrate and succinate) and inhibitors (pyruvate and oxaloacetate) under light and dark conditions at 2,4-D concentration. This occurs at the same time in overriding the herbicidal stress linked to the adjustment of the cellular redox of regulatory sites using dithiothreitol. This shows that Azolla can quench 2,4-D, which suggests  NADP-ME  as a biomarker through its sensitivity and mode of activities under xenobiotic contaminated soil.   Key words: NADP-malic enzyme, aquatic fern, herbicide, modulators, malate.