The Chemical Fingerprint of Stress: How Radioactive Contamination Changes the Structure of Lignin <i>in Sorbus aucuparia</i>

Abiotic stresses affect major processes of higher plants, including the lignification of plant tissue and, consequently, lignin chemical structure. This work presents data on the influence of ionizing radiation factors on the structure of stress lignins of Sorbus aucuparia stands grown in radioactively contaminated areas. Using ¹H-¹³C heteronuclear single quantum coherence nuclear magnetic resonance, electron paramagnetic resonance, Fourier-transform infrared and pyrolysis gas chromatography-mass spectrometry, it was found that ionizing radiation-induced stress affects the chemical structure of lignins, which was expressed in a change in the ratio of microstructural elements. The obtained results indicate an increasing amount of phenylcoumaran and spirodienone and a decrease in resinol substructures. It is interesting that ionizing radiation-induced stress does not change the monomeric composition of lignins and the quantity of β-O-4 intermonomer bonds, but leads to an increasing concentration of free phenoxyl radicals, which is consistent with an increasing number of phenolic hydroxyls. We found that rowan stress lignins retain a high antioxidant activity. Understanding the chemical structure and properties of stress lignins is important for predicting the long-term effects of chronic radiation exposure on plants, as well as for their rational use in scenarios of changing the ecology of territories.