Physiological response of Populus nigra 'Italica' to galling aphids feeding.

Although gall-inducing aphids, namely Pemphigus bursarius (L.) and P. phenax Borner et Blunck are widely known as serious pests for their secondary hosts (lettuce and carrot, respectively), the physiological mechanism of their gall induction on Populus L. trees still requires a better understanding. In this study, we compared physiological parameters, such as hydrogen peroxide (H2 O2 ), electrolyte leakage (EL ), malondialdehyde (MDA), ascorbate peroxidase (APX) and guaiacol peroxidase (GPOD). Changes in physiological parameters were analyzed in foliar tissues with galls and gall tissues themselves and compared to leaves without galls. Significantly higher H2 O2 levels were observed in P. phenax galls when compared to the leaves with galls. In turn, the highest EL from the cells and MDA content was noted in P. bursarius galls. Other samples showed lower or similar oxidative stress marker levels to leaves without galls. APX and GPOD had a similar activity profile in galls of both aphid species. Their activity decreased significantly in gall tissues, where it was even 10-fold lower than in leaves without galls. Data generated in this study indicate that pattern of the physiological features, e.g. ROS accumulation and cell membrane integrity, of Populus leaves with galls and galls alone depends on gall-inducing aphid species. Whereas, decrease of APX and GPOD activity, especially in gall tissues indicated a reduction in the antioxidant potential of these neoformed structures.