Antioxidant Defense, Lignin Biosynthesis and Hormone Signaling Coordinately Mediate the Response of Solanum tuberosum L. to Alkaline Salt Stress

Alkaline salt stress is an important abiotic stress factor that restricts the growth and development of potato (Solanum tuberosum L.). It can induce oxidative damage, disrupt cellular structures, and disturb endogenous hormone homeostasis, thereby impairing normal plant growth and development. However, the physiological mechanisms underlying potato responses to alkaline salt stress, as well as the relationships among antioxidant defense, lignin accumulation, and changes in endogenous hormone levels, remain to be fully elucidated. Therefore, a systematic investigation of potato responses to alkaline salt stress at both the physiological and gene expression levels is needed to provide further insights into the underlying stress-response mechanisms. In this study, potato cultivar ‘Atlantic’ was used as the experimental material, and a pot experiment was conducted with four NaHCO3 concentrations: 0 mmol/L (CK), 20 mmol/L (T1), 40 mmol/L (T2), and 60 mmol/L (T3). Changes in the antioxidant system, root lignin accumulation, and endogenous hormone contents under different levels of alkaline salt stress were quantitatively analyzed. In addition, the expression patterns of genes involved in lignin biosynthesis (phenylpropanoid pathway) and ABA, GA, and BR signaling pathways were examined to establish an integrated model of the responses involving antioxidant defense, hormone regulation, and lignin biosynthesis. The results showed that the degree of oxidative stress progressively increased with increasing NaHCO3 concentration. SOD (superoxide dismutase) activity and the contents of MDA (malondialdehyde) and GSH (glutathione) continuously increased, whereas POD(peroxidase) and CAT (catalase) activities exhibited a pattern of first increasing and then decreasing, reaching their maximum levels under 40 mmol/L NaHCO3 treatment. Root lignin content increased progressively with increasing stress intensity. In addition, alkaline salt stress significantly affected endogenous hormone levels, with ABA and BR contents increasing and GA content decreasing as the NaHCO3 concentration increased. Further analysis revealed that alkaline salt stress altered the expression of genes involved in the phenylpropanoid pathway and ABA (abscisic acid), GA (gibberellin), and BR (brassinosteroid) signaling pathways, indicating coordinated responses involving antioxidant defense, lignin biosynthesis, and hormonal regulation. In conclusion, potato responds to alkaline salt stress by enhancing antioxidant defense, promoting lignin accumulation, and modulating endogenous hormone balance, which may contribute to its adaptation to alkaline salt stress. This study provides insights into the regulatory mechanisms underlying potato responses to alkaline salt stress and provides a theoretical basis for stress-resilient potato cultivation and the breeding of salt- and alkali-tolerant cultivars in saline-alkali soils.