The concentration of plant photosynthetic pigments (i.e., chlorophylls a and b, and carotenoids) and chlorophyll degradation enzyme (i.e., chlorophyllase, oxidative bleaching, and Mg-dechelatase) activities on aphid-damaged and non-damaged regions of infested leaves were etermined. Diuraphis noxia (Mordvilko) feeding caused significant losses of chlorophylls a and b and carotenoids in the damaged regions. However, Rhopalosiphum padi (L.) feeding did not cause any significant losses of plant pigments between the damaged and non-damaged regions, except a significantly lower level of carotenoids was observed from the 6-d sample. Interestingly, the non-damaged regions of D. noxia-infested leaves on both sampling dates showed a significant increase of chlorophylls a and b and carotenoid concentrations when compared with uninfested leaves. The 12-d leaf samples showed that D. noxia feeding caused significant changes in the chlorophyll a/b ratio, but not chlorophyll (a+b)/carotenoid ratio between the damaged and non-damaged regions. However, neither of the ratios was significantly different from the 6-d samples. Further assays of chlorophyllase and oxidative bleaching activities showed no significant differences between the damaged and non-damaged regions. However, Mg-dechelatase activity was significantly higher in D. noxia-damaged than non-damaged leaf regions on d 6, while no differences were detected on d 12. Mg-dechelatase activity in D. noxia-infested leaves was significantly higher than in either uninfested or R. padi-infested leaves on both sampling dates. Furthermore, Mg-dechelatase activity from D. noxia-infested leaves increased significantly between 6 and 12 d. We infer that non-damaged regions of D. noxia-infested leaves compensate for the pigment losses in the damaged regions, and that Mg-dechelatase activity changed dynamically from a localized response on d 6 to a systemic response on d 12.
Species 1: Hemiptera Aphididae Diuraphis noxia (Russian wheat aphid)
Species 2: Hemiptera Aphididae Rhopalosiphum padi (bird cherry-oat aphid)
Keywords: chlorosis, Mg-dechelatase
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA