Structural features of stress lignin of aspen (Populus tremula L.) growing under increased background radiation

Abstract

Natural lignins play a key physiological role in plant responses to various biotic and abiotic stresses throughout the life cycle of a plant organism. Radiation influence is a powerful anthropogenic factor that can disrupt the normal functioning of plants, which are forced to adapt to changing environmental conditions. This work was aimed at assessing the effect of radiation factors on the chemical structure of stress lignins from aspen stands that have passed the main stages of ontogeny in radioactively contaminated areas. As a result of our research the chemical composition of stress lignins, the quantitative ratios of guaiacyl, syringyl, and p-coumaric structural units, as well as main types of intermonomer bonds, were determined. Radioactive stress resulted in changing chemical structure of lignins expressed in the increasing quantity of syringyl units and decreasing proportion of guaiacyl and p-coumaric units. In the paper a novel estimation of the quantity of intermonomer ether bonds, substructures of resinol, phenylcoumaran, and dibenzodioxocin was presented. It was determined that radiation stress leads to increasing number of ether bonds and decreasing number of other types of intermonomer bonds. Conclusions about the effect of exogenous radiation factors on the chemical structure of stress lignins were confirmed by the results of correlation analysis of experimental data. The results on the stress lignin structure are relevant from the perspective of plant physiology. For the first time, data on the paramagnetic and antioxidant properties of stress lignins have been obtained, which might result in new ways of practical use of lignins.