Deciphering morphological and biochemical modulations in mungbean by application of ethylene precursor and inhibitors under cadmium stress

Cadmium (Cd), being one of the most toxic elements, exerts negative effects on plant growth and development. Ethylene (ET) has a prime significance in abiotic stress-induced cellular modulations and regulation of plant development. In the present study, seeds of a Cd-tolerant (NM-98) and -sensitive (NM-28) genotype were primed using 50 µM ACC (ET precursor 1-amino cyclopropane-1-carboxylic acid) and ET inhibitors (1 mM AVG/aminoethoxyvinylglycine, 0.5 mM PZA/pyrazinamide or 0.25 mM AgNO₃/silver nitrate). Subsequently, these were allowed to grow in soil containing 0 or 50 µM CdCl₂. After germination, ACC, AVG, PZA or AgNO₃ was again applied, accordingly, as foliar spray. In NM-98, application of ACC resulted in reduced root fresh (38%) and dry (38%) weight, shoot fresh weight (39%), total phenolics (22%), catalase/CAT and peroxidase/POD activity (21% and 16%, respectively) under Cd stress. Contrarily, application of inhibitors (AVG, PZA and AgNO₃), under Cd stress, improved plant biomass, photosynthetic pigments, total phenolics, total soluble proteins, activity of CAT and POD in NM-98 as compared to NM-28 genotype that exhibited opposite response. It was concluded that contrasting modulations observed in NM-98 and NM-28 towards exogenous ACC (or inhibitors) was linked with Cd-tolerance level of the two genotypes where exogenous ACC likely significantly raised endogenous ET level in NM-98 leading to disrupted antioxidants status and reduced growth. However, AVG, PZA and AgNO₃ maintained ET levels and thus NM-98 exhibited less oxidative stress. Meanwhile, exogenous ACC assisted growth of NM-28 in Cd-stressed soil by modulating the antioxidative defence mechanism, possibly by maintaining endogenous ET concentrations. Further molecular-level research is recommended to investigate the underlying mechanisms associated with each component of ET biosynthesis.