Priming with quinoa dehulling residues induces changes in gene expression, boosts antioxidant defense, and mitigates salt stress in Arabidopsis thaliana L

Biostimulants help plants to cope with abiotic stresses and using those obtained by recycling waste bioproducts is an eco-friendly technology with great potential. Quinoa (Chenopodium quinoa Willd.) is a highly nutritious grain originally cultivated in the Andes but now spreading worldwide. Before consumption, quinoa seeds undergo a dehulling process that produces large amounts of a waste product rich in saponins and other bioactive compounds. In this study, the by-product of quinoa seed dehulling (quinoa hull powder, QHP) was analysed for its plant biostimulant activity. The objective was to analyze whether QHP could improve growth and induce biochemical and transcriptional changes under control or saline (25, 50, and 100 mM NaCl) conditions in the model plant Arabidopsis thaliana. QHP was supplied either by pre-soaking seeds prior to sowing (seed priming) or added to the seedling growth medium. Complete and partial recovery of germinability to control levels was observed in seeds primed with 0.05 mg mL^-1 QHP in the presence of 50 and 100 mM NaCl, respectively. Seedlings transferred to QHP-supplemented saline medium showed improved shoot and root biomass and primary root length as well as reduced oxidative stress (MDA, and H₂O₂ production). RT-qPCR analysis of stress-responsive genes revealed that some were induced by QHP alone while salt-induced expression of others was modulated by QHP. The phytochemical composition of QHP suggests that, in addition to saponins, protective compounds, such as proline, spermidine, carotenoids, and polyphenols, could be potentially responsible for its activity.