Water deficit induced by polyethylene glycol leads to the depletion of phenolic compounds but did not alter lignification in roots of Scots pine (Pinus sylvestris)

Global climate change is accompanied by an increase in the frequency and severity of droughts, which negatively impact plant growth. One of the protective mechanisms that allows plants to withstand the negative drought effects is the lignification of vascular and dermal tissues, which prevents water loss. Despite some progress in research on lignification in model and crop plants, the characteristics of lignin accumulation in conifers need further investigation. In this study, we examined the adaptation of Scots pine (Pinus sylvestris) seedlings to water deficit at weak (-0.15 MPa) and strong (-0.5 MPa) intensities induced by polyethylene glycol 6000. Our results showed that water deficit did not cause oxidative stress in the seedlings. The most significant effect of water deficit was the depletion of phenolic compounds (flavonoids, catechins, and proanthocyanidins) in seedling roots during the stress imposition period, despite no changes in the phenolic content of the needles. In this context, the lignin content in plant roots was maintained at a level comparable to that of the control. These findings indicate that root lignification in Scots pine seedlings is a stress-resistant process that is important for protecting roots under drought conditions.