Defense responses of Thuja orientalis to infestation of anholocyclic species aphid Cinara tujafilina

Abstract

The aim of this study was to determine an interdependence between generation of semiquinone radicals, superoxide anion (O2–), manganese ions (Mn2+) and phenolic content in leaves of Thuja orientalis in response to infestation by varying populations of Cinara tujafilina, i.e. 40 or 80 aphids per plant. Also, superoxide dismutase (SOD) and β-d-glucosidase activities in leaves of T. orientalis in a defense response to C. tujafilina was recorded. Analyses of electron paramagnetic resonance (EPR) showed generally a higher concentration of semiquinone radicals with g-values of 2.0051 ± 0.0005 and 20032 ± 0.0005 after C. tujafilina infestation in leaves in comparison to the control. Up to 48 h post-infestation in leaves infested by 80 aphids the level of semiquinone radicals was significantly higher than in the control, while in leaves infested by 40 aphids the highest concentrations of these radicals were recorded at later time points (i.e. at 72 and 96 hpi). In parallel, the highest total generation of O2– and low activity of SOD were recorded in 24-h leaves infested by 80 aphids. Additionally, analysis of confocal images showed that the strongest yellow fluorescence indicating O2– generation was detected in epidermal cells of leaves up to 48 hpi. Significant reduction of Mn2+ ions detected by EPR spectroscopy in relation to the control was observed in 4-w leaves infested by 80 and 40 aphids and in 48-h leaves infested by 40 aphids. Phenolic contents in leaves infested by 80 and 40 aphids at all time points were higher than in the control. The greatest β-d-glucosidase activity and phenolic contents were recorded at 96 h of feeding. These results indicate that the perception of C. tujafilina infestation by T. orientalis leaves induces a specified sequence of defense mechanisms in the course of time.