ABA hormone plays unexpected role in how plants respond to salt stress

Nearly a quarter of the world’s irrigated agricultural land is affected by salinisation. Rising sea levels, increasing droughts, and higher temperatures due to climate change are exacerbating this problem. As a result, the demand for crops that are more resistant to salinisation is growing. However, fundamental knowledge about how plants respond to acute salt stress is still lacking.

A new study by researchers from Wageningen University & Research (WUR), published in PNAS, now shows that sodium stress causes cell damage and changes in DNA regulation within the first few hours. Surprisingly, these effects are suppressed by the stress hormone ABA.

Salt stress: more than just water deprivation

To achieve these results, the researchers analysed the rapid response to table salt (NaCl) through experiments with the model plant Arabidopsis thaliana. Salt induces stress in two ways: by drawing water away (osmotic stress) and by accumulating toxic sodium ions.

By comparing NaCl with sugars, which only cause osmotic stress, and with other salts, the researchers discovered specific plant responses to sodium ions. These reactions were particularly evident within the first six hours after salt exposure but disappeared thereafter. This pattern was uncovered because the researchers focused on these early time points. Previous studies often examined effects after days or weeks, overlooking this early dynamic.

ABA suppresses damage caused by sodium ions

A subsequent step in the experiment revealed that the stress hormone ABA, which accumulates slowly during osmotic stress, suppresses the response to sodium ions. According to researcher Jasper Lamers, this suggests that both stress factors are more closely linked than previously thought.

Lamers and his colleagues then investigated what happens when ABA is present at the onset of salt stress. “When plants were pre-treated with ABA, the sodium responses were completely suppressed. The cells showed no visible damage, and sodium-induced gene regulation remained unchanged. Additionally, it became clear that the root tip is the most sensitive part of the plant to salt stress,” he explains.

Geen zout en geen ABA (No salt and no ABA): the plant root develops in a normal way. The plant root has not been exposed to salt, nor has the plant been pre-treated with ABA.

Alleen zout (Salt only): the plant root is exposed to salt at the level of the black tip, while the plant is not pre-treated with ABA. From the time of salt exposure, the root fully deflects from the salt and growth stagnates.

Alleen ABA (ABA only): the plant is pre-treated with ABA but not exposed to salt. The plant root develops normally.

Zout en ABA (Salt and ABA): the plant is pre-treated with ABA and exposed to salt at the black spot. The plant root deflects slightly after exposure to salt at first, but ABA helps to suppress the sodium reaction.

New insights for developing salt-tolerant crops

This fundamental knowledge about the first hours of salt stress and the prevention of cell damage can serve as a basis for developing more salt-tolerant crops. Lamers notes: “Since activating ABA affects the entire plant, my former colleagues in plant physiology are conducting follow-up research to determine whether it is possible to regulate this response locally—for example, in the more salt-sensitive parts of the root. I am currently working as a postdoctoral researcher in the Biochemistry department of WUR, studying how plants perceive and respond to physical forces.”