Wheat seedlings treated with carbon monoxide before being exposed to high salt levels showed improved growth and reduced water loss. This was due to an increase in proline content in the roots, which helped protect the plants from salt-induced damage. The carbon monoxide treatment activated a key enzyme involved in proline production and decreased the activity of another enzyme that breaks down proline. This study suggests that carbon monoxide pretreatment can enhance salt tolerance in wheat seedlings by increasing proline levels in the roots.