Chronic exposure to ionizing radiation elicits growth inhibition and a dynamic oxidative stress response in the shoots of scots pine (Pinus sylvestris) seedlings

Abstract

Radioactive contamination represents a significant environmental stressor and can result in long-term exposure of terrestrial ecosystems to harmful levels of ionizing radiation. While Scots pine (Pinus sylvestris) has become a cornerstone reference species for environmental radiation protection studies due to its pronounced radiosensitivity, the underlying physiological mechanisms governing its responses to chronic low-dose radiation exposure remain poorly characterized. We therefore investigated the effect of chronic gamma irradiation on the growth and the oxidative stress response of young pine seedlings. The plants were exposed to 682 μGy·h⁻¹ for 10 weeks, with phenotypical measurements and analysis of molecular and biochemical markers of oxidative stress measured at two-week intervals. Chronic exposure induced significant inhibition of shoot development and a transient reduction of axillar bud formation, correlating with a dynamic oxidative stress response. An initial stress phase involved a significant disruption of the antioxidant system, evidenced by elevated glutathione oxidation and suppressed antioxidative enzyme activities. Despite this disruption, seedlings demonstrated the capacity for swift stress acclimation, first re-establishing glutathione homeostasis through an increase in its reduced form and then transitioning to an enhanced defensive state characterized by elevated superoxide dismutase activity and increased expression of ascorbate peroxidase. Understanding the dynamic radiation stress response during seedling establishment of this keystone forest species may prove beneficial for predicting ecosystem resilience and informing environmental radiation protection strategies in radioactively contaminated environments.