Members of the genus Cuscuta are generally considered to be non-photosynthetic, stem-holoparasitic flowering plants. Under certain circumstances, at least some members of the genus are capable of limited photosynthesis. The galls of the Smicronyx weevils formed on Cuscuta campestris are particularly rich in chlorophylls compared to the stem of the parasitic plant. In the present study, we aimed to characterize the photosynthetic activity in the inner and outer gall cortices in comparison to the non-photosynthetic stems and a reference plant (Arabidopsis thaliana). The recorded prompt chlorophyll fluorescence transients were analyzed using JIP test. Detailed analysis of the chlorophyll fluorescence confirmed the presence of actively functioning photosynthetic machinery, especially in the inner cortex of the galls. This photosynthesis, induced by the insect larvae, did not reach the levels of the photosynthetic activity in Arabidopsis thaliana plants. Thylakoid protein complexes were identified by separation with two-dimensional Blue Native/SDS PAGE. It appeared that some of the complexes presented in A. thaliana are missing in C. campestris. We hypothesize that the insect-triggered transition from non-photosynthetic to photosynthetic tissue in the gall is driven by the increased requirements for nutrients related to the larval nutrition.
Parasitic flowering plants represent a diverse group of angiosperms, ranging from exotic species with limited distribution to prominent weeds, causing significant yield losses in agricultural crops. The major damage caused by them is related to the extraction of water and nutrients from the host, thus decreasing vegetative growth, flowering, and seed production. Members of the root parasites of the Orobanchaceae family and stem parasites of the genus Cuscuta are among the most aggressive and damaging weeds, affecting both monocotyledonous and dicotyledonous crops worldwide. Their control and eradication are hampered by the extreme seed longevity and persistence in soil, as well as their taxonomic position, which makes it difficult to apply selective herbicides not damaging to the hosts. The selection of resistant cultivars is among the most promising approaches to deal with this matter, although still not widely employed due to limited knowledge of the molecular mechanisms of host resistance and inheritance. The current review aims to summarize the available information on host resistance with a focus on agriculturally important parasitic plants and to outline the future perspectives of resistant crop cultivar selection to battle the global threat of parasitic plants.
The weevil gall contains two distinct regions, differing in hydrolytic and antioxidant enzymes activity and profiles, which is also functionally distinct from the non-infected Cuscuta stems. Weevils of the genus Smicronyx are gall-forming insects, widely distributed on parasitic flowering plants of the genus Cuscuta. Thus, they are considered epiparasites and potential method for biological control of their agriculturally harmful hosts. Although several reports on gall formation in Cuscuta spp. exist, the metabolic and functional changes, occurring in the gall, remained largely unknown. Smicronyx sp. galls, collected from a wild Cuscuta campestris population, were dissected into two distinct regions, inner and outer cortex, defined by the higher chlorophyll content of the inner cortex. Based on hydrolytic and antioxidant enzymes activity and isoenzymatic profiles as analyzed after electrophoretic separation, we suggested that the gall differs in its metabolic activity from the non-infected plant tissue. While the outer cortex serves as a region of nutrient storage and mobilization, the inner cortex is directly involved in larvae nutrition. The increase in metabolic activity resulted in significantly increased superoxide dismutase activity in the gall, while several other antioxidant enzymes diminished. The present research offers new insights into the functionally differing regions of Smicronyx galls and the metabolic changes, induced in C. campestris in result of the gall formation.
Plants are continuously subjected to changing environmental factors, often growing in suboptimal conditions. Due to the negative impact on agricultural yield numerous researches are published every year, studying the stress response and adaptation in plants to stress factors. Most of the studies, however, are dedicated to a single stress factor. In the present study, we examined the effect of a different combination of stresses on the chitinase profile of Arabidopsis plants. First, soil salinity (abiotic stress) was applied by irrigation with 150 mM NaCl. The plants were either infected or not with the parasitic flowering plant Cuscuta campestris Yunck. (dodder) and further challenged with the herbivorous attack – the larvae of either the sciarid fly Lycoriella ingenua (Dufour, 1839) or the citrus flatid planthopper Metcalfa pruinosa (Say, 1830). It was found that salinity and Cuscuta parasitism suppressed the response of Arabidopsis to sciarid flies, simultaneously with induction of chitinases in terms of the number of isoforms and relative activity in the parasite itself. Meanwhile, in the presence of Cuscuta, M. pruinosa tend to feed predominantly on the parasitic plant, completely ignoring the host. This was accompanied by the appearance of new chitinases, also suppressed by salinity. These results suggest complicated, antagonistic interactions between abiotic and different biotic stresses. It was also shown that the parasite is sensing the herbivore attack indirectly (in the case of L. ingenua) and transferring the stress signal to the host (in the case of M. pruinosa).
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