Dynamic change in photosynthetic pigments and chlorophyll degradation elicited by cereal aphid feeding

The concentration of 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 the infested leaves were determined with two infestation periods (6 and 12 days). Russian wheat aphid [Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae)] feeding caused significant losses of chlorophylls a and b and carotenoids in the damaged regions. However, bird cherry‐oat aphid [Rhopalosiphum padi (L.) (Hemiptera: Aphididae)] feeding did not, except a significantly lower level of carotenoids was observed in the damaged regions from the short‐infestation (6‐day) samples. Interestingly, the non‐damaged regions of D. noxia‐infested leaves on both sampling dates had a significant increase of chlorophylls a and b and carotenoid concentrations when compared with the uninfested leaves. Although D. noxia feeding did not cause any changes in either chlorophyll a/b or chlorophyll (a+b)/carotenoid ratio between the damaged and non‐damaged leaf regions on short‐infestation (6‐day) samples, a significantly lower chlorophyll a/b ratio was detected in long‐infestation (12‐day) samples. The assays of chlorophyllase and oxidative bleaching activities showed no significant differences between the damaged and non‐damaged regions of the infested leaves on either sampling date. Mg‐dechelatase activity, however, was significantly higher in D. noxia‐damaged than non‐damaged leaf regions from the short‐infestation samples, while no differences were detected from the long‐infestation samples. Furthermore, the long‐infestation samples showed that Mg‐dechelatase activity from both D. noxia‐damaged and non‐damaged regions increased significantly in comparison with the respective regions of either uninfested or R. padi‐infested leaves. 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 to a systemic response as infestation duration extends. The findings from this study on cereal aphid‐elicited chlorosis (or desistance) would help us to elucidate plant resistance mechanisms, in particular plant tolerance to non‐defoliating herbivory.