Salinity-Modulated Germination and Metabolic Reprogramming in Quinoa Seedlings: Genotype-Dependent Effects on Nutritional and Bioactive Compounds and Prospects for Microgreen Valorization

Germination is highly sensitive to abiotic stresses such as salinity, which can impair seedling establishment and seed reserve mobilization. Quinoa is a promising crop due to its salinity tolerance and high nutritional value. This study evaluated the effects of NaCl-induced salinity on germination performance, metabolic responses, and nutritional quality of three quinoa seed lots representing two varieties, Regalona (Q1) and Amarilla sacaca (Q2, Q3). Salinity significantly reduced germination rate and kinetics, as well as radicle and shoot growth, with the strongest effects at 500 mM NaCl. During the germination process, starch and protein contents decreased, reflecting reserve mobilization, while vitamin E increased under moderate salinity, particularly in Q1 and Q2, but declined under severe stress. Secondary metabolites, including phenolics, flavonoids, tannins, and saponins, exhibited strong genotype- and stress-dependent variation. HPLC-DAD identified gallic, syringic, vanillic, caffeic, and protocatechuic acids, as well as rutin, quercetin, and kaempferol, with marked differences between raw seeds and seedlings. At moderate salinity (300 mM NaCl), TFC increased by 22% and 42% in Q1 and Q2, respectively, relative to RS, whereas Q3 showed a 45% reduction. Under high salinity (500 mM NaCl), TFC decreased by 83% and 15% in Q1 and Q2, respectively, while Q3 exhibited a 35% increase relative to RS. These contrasting responses highlight genotype-dependent changes in flavonoid accumulation and reflect distinct metabolic plasticity among quinoa genotypes. Overall, these findings support quinoa as a promising functional microgreen crop for producing nutrient- and bioactive-rich foods under controlled conditions.