Assessing oxidative stress and photosynthetic activity in leaf galls induced by different species of galling insect on Aspidosperma spp.

The high levels of oxidative stress detected in gall tissues, the production of phenolic derivatives as scavengers of these molecules, and the changes in the gall photochemical efficiency have been related to the feeding behavior of galling insects. Herein, we evaluated the oxidative stress, photochemical parameters and pigment contents in four leaf galls on Aspidosperma spp. induced by 2 psyllids and 1 cecidomyiid. A. spruceanum is induced by scraping-sucking insects, while A. australe, A. macrocarpon and A. tomentosum by phloem-sucking insects. Also, anatomical and histochemical analyses, as well as phenolic and lipid peroxidation assays, were performed. The concentration of malondialdehyde seems to be a good indicator of advanced oxidative stress in gall tissues. The biosynthesis of phenolic derivatives was similar between galls and non-galled leaves, as well as among galls induced by different gallings. The total chlorophyll and chlorophyll a and b contents were higher in non-galled leaves than in galls. Fv/Fm (maximum quantum yield), NPQ (non-photochemical quenching during light adaptation) and Rfd (fluorescence decline ratio in steady-state) had lower values in galls and may be related to a loss of photochemical efficiency. Among galls, just F0 (minimal fluorescence in the dark-adapted state) and Fm (maximum fluorescence in the dark–adapted state) showed differences, with a higher F0 values in the galls of A. australe, one of the less stressful systems. Our results describe several underlying mechanisms related to the impact of feeding activity of different galling insects in gall tissues.