Effects of nitric oxide on growth and nitrogen metabolism of quinoa seedlings under saline alkali stress

In order to explore the physiological response of quinoa seedlings to exogenous NO under saline alkali stress, Longli No. 4 was used as an experimental material to treat quinoa seedlings with eight leaves at one heart stage with SNP and five mixed saline alkali solutions with different pH (200 mmol·L⁻¹). The effects of exogenous NO (150 μmol·L⁻¹) on the growth and nitrogen metabolism of quinoa seedlings under saline alkali stress were studied from three aspects: quinoa seedling growth, and the activity of enzymes related to nitrogen metabolism and nitrogen-containing compounds. The results showed that the plant height, biomass, and nitrate reductase (NR) and glutamine synthetase (GS) activities of quinoa seedlings showed a downward trend under saline alkali stress, and a greater decline with the intensification of saline alkali stress. However, the root length, root:shoot ratio, soluble protein content, and total free amino acid content all showed an increasing trend, and their content increased with an increase in salinity. NO could promote the growth of the aboveground and underground parts of quinoa, and increase the activity of enzymes related to nitrogen metabolism and the content of nitrogen-containing compounds (although the content of soluble sugar showed a downward trend). Among the alkaline salt treatments, treatment D (pH 9.75) had the most obvious effect, and its root length, biomass, and NR and GS activities increased by 110%, 340%, and 51.52%, and 83.08% respectively. In conclusion, NO can significantly alleviate the growth and nitrogen metabolism of quinoa seedlings under saline alkali stress, and its alleviating effect on multi-component alkaline salt is better than that of neutral salt.