Ana Luisa Anaya

Allelopathy as a tool in the management of biotic resources in agroecosystems

In modern agriculture, natural plant communities may be replaced by a single crop species. Weeds, some microorganisms, and viruses, as well as some herbivores are organisms that should be eliminated. Pesticides and fertilizers not only affect the pests and crops, but soil, non-pest species, water, food, and humans. In traditional agriculture weeds are components with an important ecological role in the maintenance of the system. Some weeds have been used as tools to control the growth of other weeds in traditional agroecosystems. Researchers on sustainable and organic agriculture get valuable information from traditional agriculture and currently are conducting research on plant breeding, soil fertility and tillage, crop protection, and cropping systems. Allelopathy and chemical ecology are directly involved in each of these fields and can play an important role in crop productivity, conservation of genetic diversity, and maintenance of ecosystems stability. Allelopathy has been shown to be related with p...

Naphthoquinone spiroketal with allelochemical activity from the newly discovered endophytic fungus Edenia gomezpompae.

Chemical investigation of the mycelium of Edenia gomezpompae, a newly discovered endophytic fungus isolated from the leaves of Callicarpa acuminata (Verbenaceae) collected from the ecological reserve El Eden, Quintana Roo, Mexico, resulted in the isolation of four naphthoquinone spiroketals, including three new compounds and palmarumycin CP2 (4). We elucidated the structures of the metabolites by extensive NMR spectroscopy studies, including DEPT, COSY, NOESY, HSQC, HMBC, and chiroptical methods. The trivial names proposed for these compounds are preussomerin EG1 (1), preussomerin EG2 (2) and preussomerin EG3 (3). In addition, the X-ray data for 4 were obtained. The bioactivity of the mycelial organic extracts and the pure compounds was tested against three endophytic fungi (Colletotrichum sp., Phomopsis sp., and Guignardia manguifera) isolated from the same plant species (C. acuminata, Verbenaceae) and against four economically important phytopathogenic microorganisms (two fungoid oomycetes, Phythophtora capsici and Phythophtora parasitica, and the fungi Fusarium oxysporum and Alternaria solani). Spiroketals 1-3 displayed significant growth inhibition against all the phytopathogens. IC50 values for the four phytopathogens were from 20 to 170 microg/ml. Palmarumycin CP2 (4) was not bioactive against any of the fungi tested. Compound 1 showed the strongest bioactivity. The acetylated derivatives of preussomerin EG1 (1), 1a and 1b, were obtained and their biological activity was tested on endophytes and phytopathogens. Preussomerin EG1 1, 1a and 1b exhibited significant bioactivity against all microorganisms tested with the exception of Alternaria solani. This is the first report of allelochemicals with antifungal activity from the newly discovered endophytic fungus E. gomezpompae.

Effects of Allelochemical Stress Produced by Sicyos deppei on Seedling Root Ultrastructure of Phaseolus vulgaris and Cucurbita ficifolia

The allelopathic potential of the cucurbit Sicyos deppei has been reported. Aqueous leachates (1% w/v) of S. deppei significantly inhibited the radicle growth of several test plants. Root tips of treated plants were thicker, with a brownish color as compared to control roots. Light microscope observations of treated root tips of Phaseolus vulgaris showed that cells around the quiescent center appeared compressed. Tissues were disorganized and lacked evident cell differentiation. Cucurbita ficifolia did not show these differences in root morphology. Scanning and electron microscope observations showed that treated roots of both P. vulgaris and C. ficifolia had ultrastructural alterations of certain organelles, the plasma membrane, and cell walls. Root cap cells of treated roots showed amorphous and inactivated (nondividing) nuclei, mitochondria, and endoplasmic reticulum. Vacuoles in treated cells showed invaginations that may correspond to engulfing of damaged cellular components.

Phytotoxic compounds from Esenbeckia yaxhoob

Abstract Investigation of the aerial parts of Esenbeckia yaxhoob Lundell (Rutaceae) led to the isolation of a new dammarane-type of triterpene which was characterized by spectral means as (24S)-24-methyl-dammara-20,25-diene-3β-yl-acetate. In addition, 2-tridecanone, asarinin, imperatorin, lupeol and hesperidin were obtained. (24S)-24-Methyl-dammara-20,25-diene-3β-yl-acetate, 2-tridecanone, asarinin and imperatorin caused significant inhibition of the radicle growth and\or germination of seedlings of Amaranthus hypochondriacus, Echinochloa crusgalli, Lactuca sativa and Lycopersicum esculentum. Also, it has been found that imperatorin inhibited ATP synthesis and both phosphorylating and uncoupled electron flow from H2O to K3[Fe(CN)6]. On the other hand, this coumarin stimulated the basal electron flow from H2O to K3[Fe(CN)6] and the activity of the light-activated Mg2-ATPase. These effects were measured in freshly lysed illuminated spinach chloroplasts and allowed to determine that imperatorin acts as an uncoupler and as a Hill reaction inhibitor.

Perspectives on allelopathy in mexican traditional agroecosystems: A case study in tlaxcala.

Agroecosystems in Tlaxcala, Mexico, are surrounded by trees and water channels and have a great variety of cultivated and noncultivated plants. The main results of a study carried out on a traditional agroecosystem in Santa Inés, Tlaxcala are presented. Some ecological aspects of polycultures, plant covers (dry leaves ofAlnus firmifolia, Berula erecta, andJuncus sp.), and the allelopathic potential of crops and noncultivated plants (fresh and dry material) were analyzed. The main plants (trees, shrubs, and herbs) present in the agroecosystem were identified. The total number of weeds in plots where plant covers were added was reduced. The number of nodules ofRhizobium phaseoli and the production of bean and squash increased with plant covers. Corn, beans, and squash showed a clear allelopathic effect, as well asChenopodium murale, Tradescantia crassifolia, Melilotus indicus, andAmaranthus hybridus, among other weeds. The contribution of allelopathy in studies of traditional agroecosystems is of great importance for the management of species in space and time. Allelopathy can be the basis of biological control of pests and weeds and of the discovery of new useful substances.

Allelopathic potential of compounds isolated fromIpomoea tricolor cav. (Convolvulaceae)

The allelopathic potential ofI. tricolor, used in traditional agriculture as a weed controller, has been demonstrated by measuring the inhibitory activity of aqueous lixiviates and organic extracts of the plant material on seedling growth ofAmaranthus leucocarpus andEchinochloa crusgalli. Bioactivity-guided fractionation of the most active organic extract led to the isolation of the allelopathic principles, which turned out to be a mixture of glycosides, having jalapinolic acid as the aglycone portion glycosidically linked in the 11 position to an oligosaccharide composed of glucose, rhamnose, and fucose, which also combines with the carboxyl group of the aglycone to form a macrocyclic ester.

Effect of some sesquiterpenic lactones on the growth of certain secondary tropical species

Results of biotests carried out with several sesquiterpene lactones produced byAmbrosia cumanensis are presented. These compounds showed different effects on the germination and growth of several species of the secondary vegetation of a tropical zone of Mexico.

Allelochemical stress can trigger oxidative damage in receptor plants: mode of action of phytotoxicity.

Plants can interact with other plants through the release of chemical compounds or allelochemicals. These compounds released by donor plants influence germination, growth, development, and establishment of receptor plants; having an important role on the pattern of vegetation, i.e as invasive strategy, and on crop productivity. This phytotoxic or negative effect of the released allelochemicals (allelochemical stress) is caused by modifying or altering diverse metabolic processes, having many molecular targets in the receptor plants. Recently, using an aggressive and allelopathic plant Sicyos deppei as the donor plant, and Lycopersicon esculentum as the receptor plant, we showed that the allelochemicals released by S. deppei caused oxidative damage through an increase in reactive oxygen species (ROS) and activation or modification of antioxidant enzymes. Based on this study, we proposed that oxidative stress is one of the mechanisms, among others, by which an allelopathic plant causes phytotoxicity to other plants.

Screening for Effects of Phytochemical Variability on Cytoplasmic Protein Synthesis Pattern of Crop Plants

Crop plants have to cope with phytochemical variability along with other environmental stresses. Allelochemicals affect several cellular processes. We tested the effect of toxic aqueous leachates from Sicyos deppei, Acacia sedillense, Sebastiania adenophora, and Lantana camara on the radicle growth and cytoplasmic protein synthesis patterns of Zea mays (maize), Phaseolus vulgaris (bean), Cucurbita pepo (squash), and Lycopersicon esculentum (tomato). 2D-PAGE and gel scan densitometry analysis were used to detect differences in cytoplasmic root protein pattern expression. High-, medium-, and low-molecular-weight cytoplasmic proteins were affected by the different aqueous leachates. Crop plant responses were diverse, but in general, an increase in protein synthesis was observed in the treated roots. Maize was the least affected, but both the radicle growth and also the protein pattern of tomato were severely inhibited by all allelopathic plants. The changes observed in protein expression may indicate a biochemical alteration at the cellular level of the tested crop plants.

Phenylacetic acid as a phytotoxic compound of corn pollen.

Phenylacetic acid (PAA), one of the phytotoxic compounds in corn (Zea mays) pollen, was identified by GC-MS and by direct comparison with a pure commercial sample of PAA. Bioassays were carried out by testing whole pollen, methylene chloride extract of the pollen, and pure PAA on germination and radical growth ofAmaranthus leucocarpus andEchinochloa crusgalli. The effect of corn pollen was compared with that ofZea mexicana (Teosinte), one of the wild relatives of cultivated maize.