Iridoid Glycosides Isolated from Bellardia trixago Identified as Inhibitors of Orobanche cumana Radicle Growth

Abstract

Orobanche cumana is an obligate holoparasitic plant with noxious effects in sunflower crops. Bellardia trixago is a facultative hemiparasitic plant that infects ruderal plants without noxious significance in agriculture and is known to produce a wide spectrum of bioactive metabolites. The objective of this study was to evaluate the allelopathic effects of B. trixago on the growth of O. cumana seedlings. Three different extracts using solvents of increasing polarity (n-hexane, dichloromethane and ethyl acetate) were prepared from the flowers, aerial green organs and roots of two populations, a white-flowered and a yellow-flowered population of B. trixago, both collected in southern Spain. Each extract was studied using allelopathic screenings on O. cumana which resulted in the identification of allelopathic activity of the ethyl acetate extracts against Orobanche radicles. Five iridoid glycosides were isolated together with benzoic acid from the ethyl acetate extract of aerial green organs by bio-guided purification. These compounds were identified as bartsioside, melampyroside, mussaenoside, gardoside methyl ester and aucubin. Among them, melampyroside was found to be the most abundant constituent in the extract (44.3% w/w), as well as the most phytotoxic iridoid on O. cumana radicle, showing a 72.6% inhibition of radicle growth. This activity of melampyroside was significantly high when compared with the inhibitory activity of benzoic acid (25.9%), a phenolic acid with known allelopathic activity against weeds. The ecotoxicological profile of melampyroside was evaluated using organisms representing different trophic levels of the aquatic and terrestrial ecosystems, namely producers (green freshwater algae Raphidocelis subcapitata and macrophyte Lepidium sativum), consumers (water flea Daphnia magna and nematode Caenorhabditis elegans) and decomposers (bacterium Aliivibrio fischeri). The ecotoxicity of melampyroside differed significantly depending on the test organism showing the highest toxicity to daphnia, nematodes and bacteria, and a lower toxicity to algae and macrophytes. The findings of the present study may provide useful information for the generation of green alternatives to synthetic herbicides for the control of O. cumana.

Identification of Allelochemicals with Differential Modes of Phytotoxicity against Cuscuta campestris

“…As reported above (Table 1), CLogP values were positive for almost all the compounds tested, except in the case of compounds 1 and 4, the negative CLogP values of which hint at a preference for the aqueous media, instead of the organic. As stated previously [24], high aqueous solubility may have a positive effect on bioactivity; however, this was not the case, since negligible activity was obtained for these compounds. A broad range of CLogP (higher than 0 and up to 2.445) was obtained for compounds 2, 3, 8, 9, 14 and 17, also with negligible activity, all of them being polar compounds (with amine, hydroxyl and carboxyl groups).…”

“…Thus, this level of activity might be related to interaction in the active site with specific parts of the molecules. Closer structurally-related compounds to 5, namely, 24-27, showed CLogP disparity after the addition of hydroxyl (24), benzyloxy (25), chloroacetyl (26) and halogen bromide (27). The growth inhibition activity of these derivatives dropped drastically (Figure 4).…”

“…Only compound 27, with a CLogP closest to that of compound 5 (2.021), preserved the activity level (around 80%) at the highest tested concentration (1 mM), while the rest of compounds, with disparate CLogP values, saw their bioactivities reduced to levels closer to 30%. Though this change in lipophilicity might explain the loss of bioactivity, the effect on the substitution position cannot be dismissed [24]. Derivatization of position 5 might be safer in terms of preserving the bioactivity than position 6, which might be required to be free in order to fit in the active site.…”

Characterization of Conyza bonariensis Allelochemicals against Broomrape Weeds

“…A total of 240 g of Conyza bonariensis shoots were extracted, following a previously reported protocol often used for the extraction of plant material [ 38 ]. In particular, the shoots were ground and extracted by 1.7 L H 2 O/MeOH (1/1, v/v ), under stirred conditions at room temperature for 24 h. The hydroalcoholic suspensions were centrifuged at 7000 rpm and extracted with n -hexane (3 × 800 mL), CHCl 3 (3 × 800 mL) after removing methanol under reduced pressure, with EtOAc (3 × 500 mL).…”

Production of (10S,11S)-(—)-epi-Pyriculol and Its HPLC Quantification in Liquid Cultures of Pyricularia grisea, a Potential Mycoherbicide for the Control of Buffelgrass (Cenchrus ciliaris)

“…Thus, there is an interest in improving production of EPYR to allow new, larger-scale studies, ideally under greenhouse and field conditions. The availability of good quantities of EPYR will also allow us to perform ecotoxicological studies using organisms representing different trophic levels of aquatic and terrestrial ecosystems, namely, producers (e.g., the green freshwater alga Raphidocelis subcapitata and the macrophyte Lepidium sativum ), consumers (e.g., the water flea Daphnia magna and nematode Caenorhabditis elegans ), and decomposers (e.g., the bacterium Aliivibrio fischeri ) [ 16 ]. The development of rapid and sensitive methods for the quantification of EPYR in complex mixtures is needed for these purposes, as are the requirements for modern analysis, identification, and quantification of compounds in natural samples in general [ 17 , 18 ].…”