Diego Castellano

Potential allelopathic sesquiterpene lactones from sunflower leaves

Abstract Isolation, structure elucidation and allelopathic bioassays of 13 sesquiterpene lactones, four of them new, from the sunflower cultivar VYP ® are described. Structures of the lactone assigned as 1,2-anhydrido-4,5-dihydroniveusin A, previously isolated from capitate glandular trichomes of Helianthus annuus and of annuithrin are corrected. The effect of a series of aqueous solutions at 10 −4 –10 −9 M of the sesquiterpene lactones was studied on the root and shoot lengths of Lactuca sativa var. nigra, Lepidium sativum, Lycopersicon esculentum , seedlings (dicotyledons) and Hordeum vulgare and Triticum estivum (monocotyledons). The guaianolides generally had no effect on the germination and growth of L. sativum and L. esculentum , except for C-10 epimers 8β-angeloyloxycumambranolide and annoulide G where inhibitory effects were found on the shoot length of L. esculentum . Both exhibit similar activity profiles, the most persistenty active compound on dilution was 8β-angeloyloxycumambranolide with an α-orientated hydroxyl group at C-10. The conformational changes due to functionalization within germacranolides influence principally root and shoot growth. Heliangolides have greater effect on root and shoot length of dicotyledon species, presumably due to conformational flexibility and the presence of electrophylic groups.

Bioactive flavonoids from Helianthus annuus cultivars

Abstract Isolation, structure elucidation and allelopathic bioassay of five flavonoids (the flavonol tambulin, the chalcones kukulcanin B and heliannone A, and the flavanones heliannones B and C) from the sunflower cultivar VYP® are described. Heliannones A–C are reported in the literature as natural products, for the first time. The effects of a series of aqueous solutions at 10−4–10−9 M of the flavonoids on the root and shoot length of Lycopersicon esculentum and Hordeum vulgare has been studied. They influence, principally, the shoot growth of seedlings, but germination and radical length can be affected by chalcones. The effects of very similar compounds, kukulcanin B and heliannone A, varied. The reason for this variation could be related to the number and position of free hydroxy groups.

Dehydrozaluzanin C: a potent plant growth regulator with potential use as a natural herbicide template.

The natural product dehydrozaluzanin C (former DHZ) is a sesquiterpene lactone obtained from different weeds of the Compositae family. Its potential as a plant growth regulator has been evaluated by using a phytotoxic allelopathic bioassay, where the commercial herbicide Logran is used as internal reference. The evaluation is made based on their effects on germination and growth over several dicotyledon and monocotyledon species. The activity was tested in the range of 1000-0.001 microM. In almost all cases, DHZ was more active than the internal reference at 1000 microM, and its activity fell below the level of the internal reference at 100 microM. These results confirm DHZ as a potent plant growth regulator and a good candidate for the development of new herbicide models.

Evidence for an Allelopathic Interaction Between Rye and Wild Oats

Allelopathy is a biological phenomenon in which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. Allelopathy has been the subject of a great deal of research in chemical ecology since the 1930s. The characterization of the factors that influence this phenomenon has barely been explored, mainly due to the complexity of this area. The main aim of the research carried out to date has been to shed light on the importance of these interactions in agroecosystems, especially in relation to the interactions between crops and weeds. Herein we report the characterization of a complete allelochemical pathway involving benzoxazinones, which are known to participate in allelopathic plant defense interactions of several plants of high agronomic interest. The production of the defense chemicals by a donor plant (crop), the route and transformations of the chemicals released into the environment, and the uptake and phytotoxic effects on a target plant (weed) were all monitored. The results of this study, which is the first of its kind, allowed a complete dynamic characterization of the allelopathic phenomenon for benzoxazinones.

Developing new herbicide models from allelochemicals

Plants contain allelochemicals which are their own defence systems and can act as herbicides. Selected examples of guaianolides and heliannuols, which are sesquiterpenes, are discussed in the context of their potential use as natural herbicide templates.