ALLELOPATHIC INTERACTION BETWEEN ARGEMONE MEXICANA L. EXTRACT AND NITROGEN METABOLISM IN WITHANIA SOMNIFERA (L.) DUNAL

Abstract

The invasive success of Argemone mexicana L. in semi-arid ecosystems poses a significant biological threat to the cultivation of high-value medicinal crops, particularly Withania somnifera (L.) Dunal. While the allelopathic potential of A. mexicana is frequently attributed to generalized phytotoxicity, the precise physiology remains under-characterized. This study investigates the hypothesis that A. mexicana establishes ecological dominance by disrupting the nitrogen assimilation pathway of neighbouring species, specifically targeting the rate-limiting enzyme Nitrate Reductase (NR). Elemental profiling of foliar tissues via Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was conducted to quantify essential metallo-cofactors (Mo, Fe, Zn) required for holoenzyme assembly. Baseline in vitro NR activity was determined using the NADH-dependent Griess assay, followed by kinetic studies involving the introduction of A. mexicana alkaloidal fractions to the W. somnifera reaction system. Elemental analysis revealed that A. mexicana functions as a hyper-accumulator of Iron (1408.83 mg/kg) and Molybdenum, correlating with a distinct physiological advantage in nitrogen processing. In cross-species assays, the introduction of alkaloid-rich extracts resulted in a significant, dose-dependent suppression of W. somnifera NR activity, reaching 85.3% inhibition at maximum concentration. Furthermore, post-reaction elemental analysis revealed no iron leaching into the soluble phase, indicating an allosteric or non-chelating mechanism of inhibition. These findings suggest that the invasiveness of A. mexicana is mediated not only by resource competition but by a sophisticated "biochemical warfare" strategy that compromises the primary nitrogen metabolism of nearby vegetation.