Betacyanin accumulation mediates photosynthetic protection in Suaeda salsa (L.) Pall. under salt stress.

Soil salinization threatens sustainable agriculture, necessitating innovative restoration strategies. Suaeda salsa (L.) Pall., a halophyte with exceptional salt tolerance and vivid pigmentation, serves as an ideal model for salinity adaptation. This study integrates physiological and transcriptomic analyses to reveal how high salinity (400 mmol·L⁻¹ NaCl) upregulates 4,5-DOPA dioxygenase after 30 days of salt stress, promoting betacyanin accumulation to mitigate oxidative damage. Compared to the control, betacyanin content in the 200 mmol·L⁻¹ and 400 mmol·L⁻¹ NaCl groups increased to 1.975-fold and 3.675-fold, respectively, while chlorophyll a content decreased by 45.78% and 69.88%, chlorophyll b by 11.45% and 28.24%, and total chlorophyll by 30.28% and 53.06%. This trade-off in pigment allocation highlights the plant's adaptive strategy under salinity stress. The photosynthetic characteristics of S. salsa confirm that its photoprotective mechanisms are significantly enhanced under 400 mmol·L⁻¹ NaCl. At the molecular level, betacyanin biosynthesis alleviates oxidative stress, while transcriptional regulation of photosystem I (PSI) and photosystem II (PSII) genes-such as PsbY, PsaO, PsbM, and PsbW-partially restores photosynthetic activity. Stabilization of the electron transport chain by upregulated genes like PetA and PetH further enhances photosynthetic resilience. These findings highlight the synergy between betacyanin production and photosynthetic regulation in enhancing salinity resilience, providing insights for soil restoration and salt-tolerant crop breeding.