Katarzyna Rubinowska

Physiological Response of Pedunculate Oak Trees to Gall-Inducing Cynipidae

Abstract Gall-inducing Cynipidae (Hymenoptera) manipulate the leaves of their host plants and induce local resistance, resulting in a diversity of physiological changes. In this study, three gall morphotypes caused by the asexual generation of Cynips quercusfolii L., Neuroterus numismalis (Fourc.) and Neuroterus quercusbaccarum L. (Hymenoptera: Cynipidae) on pedunculate oaks (Quercus robur L. (Fagales: Fagaceae)), were used as a model to examine physiological alterations in galls and foliar tissues, compared to non-galled tissues. Our goal was to investigate whether plant physiological response to insect feeding on the same host plant varies depending on gall-wasp species. In particular, the cytoplasmic membrane condition, hydrogen peroxide (H2O2) concentration and changes in antioxidative enzyme activities, including guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) were examined in this study. All cynipid species increased H2O2 levels in the leaves with galls, while the level of H2O2 in galls depended on the species. The presence of galls of all species on oak leaves caused an increase of electrolyte leakage and lipid peroxidation level. A significant induction of GPX activity was observed in the leaves with galls of all species, indicating stress induction. Conversely, the decrease in APX activity in both leaves with galls and galled tissues exposed to feeding of all cynipid species.

Physiological Response of Orchids to Mealybugs (Hemiptera: Pseudococcidae) Infestation

Abstract The harmfulness of mealybugs resulting from sucking plant sap, secreting honeydew, and transmitting plant viruses can give them the status of serious pests. This study documents the influence of Pseudococcus maritimus (Ehrhorn) and Pseudococcus longispinus (Targioni Tozzetti) infestation on alterations in selected physiological parameters of Phalaenopsis x hybridum ‘Innocence’. The condition of the cytoplasmic membranes was expressed as the value of thiobarbituric acid reactive substances. We have determined changes in the activities of catalase and guaiacol peroxidase and measured the following chlorophyll fluorescence parameters: maximum quantum yield of photosystem II (Fv/Fm), effective quantum yield (Y), photochemical quenching (qP), and nonphotochemical quenching (qN). The strongest physiological response of orchids was recorded in the initial period of mealybugs infestation. Prolonged insect feeding suppressed lipid peroxidation, peroxidase and catalase activity, as well as photosynthesis photochemistry. The pattern of changes was dependent on mealybug species. This indicated the complexity of the processes responsible for plant tolerance. Data generated in this study have provided a better understanding of the impact of two mealybug species infestation on Phalaenopsis and should be useful in developing pest management strategies.

Selenium biofortification enhances the growth and alters the physiological response of lamb's lettuce grown under high temperature stress

We examined the possibility to enhance the growth and the physiological tolerance of lambs lettuce (Valerianella locusta L.) grown under heat stress (HS) by biofortification with selenium (Se). The plants were grown at optimal (22/19 °C; day/night) or high (35/22 °C; day/night) temperature and Se was applied via foliar or soil treatment. The HS reduced plant biomass and photosynthetic pigment concentration and impaired some parameters of chlorophyll a fluorescence. The lambs lettuce grown under HS accumulated large amounts of H2O2 in the leaves, especially in younger ones. The Se fertilization (both foliar and soil) at HS was beneficial to plant growth, whilst the concentration of photosynthetic pigments and the analysed parameters of chlorophyll a fluorescence were unaffected by the Se supply. The application of Se enhanced the thermo-tolerance of plants through cooperative action of antioxidant enzymes, such as guaiacol peroxidase (GPOX; EC 1.11.1.7) and catalase (CAT; EC 1.11.1.6), and reduced glutathione (GSH) among low-molecular-weight non-enzymatic antioxidants, in removal of excess of H2O2. Although under HS the content of different phenolic compounds in the leaves was higher than under normal temperature (NT), the application of Se did not affect their concentration at stress conditions. On the other hand, at NT the Se-biofortified plants accumulated significantly more phenolic compounds with health-promoting properties than Se-untreated plants. Therefore, biofortification of lambs lettuce with Se can be beneficial in terms of plants yield and their nutritional value under both NT and HS.

The effect of galling aphids feeding on photosynthesis photochemistry of elm trees (Ulmus sp.)

Changes of chlorophyll (Chl) a fluorescence and photosynthetic pigment contents were analysed in galled leaves (visibly damaged and undamaged parts) and intact leaves. The values of minimal fluorescence of the dark-adapted state, maximal quantum yield of PSII photochemistry, effective quantum yield of PSII photochemical conversion, and photochemical quenching coefficient decreased in Ulmus pumila L. leaves galled by Tetraneura ulmi (L.) and in U. glabra Huds. galled by Eriosoma ulmi (L.). Colopha compressa (Koch.) feeding affected these parameters only in damaged parts of U. laevis Pall. galled leaves. The increasing number of T. ulmi galls progressively decreased photosynthetic performance. In gall tissues of all analysed aphid species, the lowest photosynthetic pigment content was found, indicating that the photosynthetic capacity must have been low in galls. Significant reduction of Chl and carotenoid contents were observed in damaged and undamaged portions of galled leaves only in the case of T. ulmi feeding.

Tetraneura ulmi (Hemiptera: Eriosomatinae) Induces Oxidative Stress and Alters Antioxidant Enzyme Activities in Elm Leaves

Abstract Gall formation is induced by an insect, which changes normal plant development and results in the formation of a new organ, following distinct stages of metabolic and developmental alterations. Research on mechanisms of recognition and responses to biotic stress may help to understand the interactions between galling aphids and their host plants. In this study, Tetraneura ulmi L. (Hemiptera: Eriosomatinae) galls and Ulmus pumila L. (Rosales: Ulmaceae) leaves were used as a model. Concentrations of hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances, electrolyte leakage, as well as the activity of ascorbate peroxidase, guaiacol peroxidase, and catalase (CAT) were determined in galls and two parts of galled leaves (with and without visible damage). Biochemical analyses were performed at three stages of gall development: initial, fully developed, and mature galls. A slight increment in H2O2 content with a strong enhancement of ascorbate peroxidase and CAT activities were observed in galls and galled leaves in the first stage. In subsequent stages of gall development, a progressing increase in H2O2 production and cell membrane damage was associated with declining antioxidant enzyme activities, especially in gall tissues. The stages of gall development are likely to be part of cell death triggered by aphid feeding. It seems that the gall is the result of a biochemical struggle between the host plant and the gall inducer.