Nitric Oxide Reduced Saponin Metabolite in Chenopodium quinoa Seedlings Cultivated under Salinity

This study explored whether the exogenously applied nitric oxide (NO; 25 µM for 12 times with 7 days intervals) triggers variations in growth, physiological traits, and molecular characteristics in quinoa Chenopodium quinoa seedlings under two electrical conductivity (EC) conditions, including 1.5 and 8 dS/m. The foliar application of NO not only increased the number of leaves produced and the biomass of the shoots under the low EC conditions, but also mitigated the risk associated with the high EC conditions. Higher proline levels were recorded in both the leaves and the roots of plants treated with NO and/or salinity among which the (NO + salinity) group had the highest amount. Both NO and high EC treatments contributed to the reduction of the saponin metabolite concentration. The highest activity of the PAL enzyme was recorded in NO-treated seedlings cultivated under high EC conditions. Total soluble phenolic and flavonoid content exhibited a similar trend to that of the PAL activity in response to the NO treatments under two EC conditions. The NO or saline treatments individually up-regulated the WRKY transcription factor by an average of 4.2-fold, while the NO treatment under the saline medium led to a drastic increase (9.7-fold) in the expression of this gene. The bZIP gene also showed a similar trend as the WRKY transcription factor gene. According to the statistical analysis, the saponin content was negatively correlated with the expression of the evaluated genes (WRKY and bZIP). In conclusion, NO confers salinity resistance and may improve the quality of quinoa-based foods by reducing saponin accumulation.