Spermidine and CaSPDS gene sustain salt tolerance in pepper seedlings

Exogenous spermidine, a polyamine involved in plant stress adaptation, alleviates the damage that salt stress inflicts on pepper seedlings by keeping reactive oxygen species accumulation in check and preserving photosynthetic function, according to a controlled seedling study published open access in BMC Plant Biology. The same work points to the spermidine biosynthesis gene CaSPDS as an essential component of the salt stress response: when the researchers silenced CaSPDS using virus-induced gene silencing, salt-treated seedlings wilted more severely and showed stronger signs of cellular damage than plants with the gene intact. The results tie a stress-protective molecule and one of its own biosynthesis genes to a shared physiological outcome, salt tolerance, through the maintenance of redox balance in young pepper plants.

The experimental picture of untreated salt stress was consistent across the measured indicators. Salt stress significantly inhibited seedling growth and reduced relative water content, chlorophyll content, the chlorophyll fluorescence parameter Fv/Fm, which reflects photosystem II efficiency, and photosynthetic gas-exchange parameters. At the same time, stressed seedlings accumulated damage-associated markers: relative electrical conductivity, an indicator of membrane leakage, rose, as did malondialdehyde content, a product of lipid peroxidation, and the reactive oxygen species hydrogen peroxide and the superoxide anion radical. Antioxidant enzyme activities increased under salt stress, a sign that the seedlings’ defense systems had been mobilized against the oxidative burden imposed by salinity.

Applying spermidine from outside the plant markedly eased these adverse effects. Treated seedlings showed improved membrane stability, maintained photosynthetic performance, reduced reactive oxygen species accumulation and modulated antioxidant defense responses compared with salt-stressed plants that did not receive the polyamine. Spermidine treatment also changed the osmotic adjustment profile of the stressed seedlings: it reduced the excessive accumulation of proline and soluble sugars that salt stress had induced, while restoring soluble protein content. Taken together, the physiological data indicate that spermidine supports salt tolerance by protecting membrane integrity and photosynthetic capacity while regulating osmotic adjustment and antioxidant defense.

Expression analysis connected these physiological effects to the polyamine biosynthesis pathway. Salt stress strongly induced genes involved in polyamine biosynthesis, particularly CaSPDS, which encodes spermidine synthase, and CaSPMS, which encodes spermine synthase. Exogenous spermidine application further enhanced CaSPMS expression in the stressed seedlings. Polyamines such as putrescine, spermidine and spermine are metabolically interconnected, and the coordinated induction of their biosynthesis genes under salt stress suggests that the pathway is actively engaged in the pepper seedlings’ response to salinity rather than being a passive bystander.

The functional test came from virus-induced gene silencing of CaSPDS. Silenced seedlings under salt stress developed more severe wilting, showed higher relative electrical conductivity and malondialdehyde contents, had lower relative water content, and displayed increased expression of ROS-related genes. This pattern of heightened membrane damage, water loss and oxidative gene activation in the silenced plants confirms an essential role for CaSPDS in salt tolerance and redox balance in pepper. The authors conclude that exogenous spermidine enhances salt tolerance in pepper seedlings by maintaining ROS homeostasis, protecting membrane integrity and photosynthetic capacity, and regulating osmotic adjustment and antioxidant defense, and that the results indicate a close association between CaSPDS and spermidine function. The study’s scope covers pepper seedlings raised under controlled salt stress conditions, so the findings describe seedling-stage mechanisms rather than field-level yield outcomes.

Subject of Research: Physiological and molecular mechanisms of spermidine-mediated salt tolerance in pepper seedlings

Article Title: Exogenous spermidine and the CaSPDS gene regulate salt tolerance by maintaining ROS homeostasis and photosynthetic function in pepper seedlings

Article References: Xu, Z., Zhao, X., Zhang, Y., Wang, S., Yu, M., Liang, Z., Song, X., & Lin, D. (2026). Exogenous spermidine and the CaSPDS gene regulate salt tolerance by maintaining ROS homeostasis and photosynthetic function in pepper seedlings. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09889-6

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09889-6

Keywords: spermidine, salt stress, pepper, ROS, photosynthesis, CaSPDS, polyamines, VIGS, antioxidant defense, plant biology, Exogenous, gene