Argemone mexicana contiene metabolitos secundarios que controlan hongos fitopatógenos

Las enfermedades en plantas ocasionadas por hongos fitopatógenos limitan la producción de cultivos a nivel mundial, hasta ahora el principal método de control han sido los fungicidas sintéticos, pero su uso descontrolado ocasiona severos problemas a la salud y al medio ambiente. Actualmente se buscan alternativas amigables con el medio ambiente; los biofungidas elaborados a base de extractos vegetales son una alternativa promisora para el control de fitopatógenos. Algunos extractos obtenidos de Argemone mexicana contienen metabolitos secundarios como: alcaloides, terpenoides, flavonoides y compuestos fenólicos, entre otros, los cuales reportan actividad biológica contra hongos que infectan cultivos de interés comercial.

Alkaloid Biosynthesis in the Early Stages of the Germination of Argemone mexicana L. (Papaveraceae)

The synthesis of the benzylisoquinoline alkaloids, sanguinarine and berberine, was monitored in Argemone mexicana L. (Papaveracea) throughout the early stages of its hypocotyl and seedling development. Sanguinarine was detected in the cotyledons right after hypocotyl emergence, and it increased continuously until the apical hook unbent, prior to the cotyledonary leaves unfolding, when it abruptly fell. In the cotyledonary leaves, it also remained at low levels. Throughout development, berberine accumulation required the formation of cotyledonary leaves, whereas it was quickly detected in the hypocotyl from the time it emerged. Interestingly, the alkaloids detected in the cotyledons could have been imported from hypocotyls, because no transcriptional activity was detected in there. However, after turning into cotyledonary leaves, important levels of gene expression were noted. Taken together, these results suggest that the patterns of alkaloid tissue distribution are established from very early development, and might require transport systems.

Alkaloid Distribution in Seeds of Argemone mexicana L. (Papaveraceae)

Seeds of Argemone mexicana L. accumulate significative amounts of sanguinarine. The analysis of the distribution of this alkaloid through the tissues of mature seeds revealed that up to 60 % of its contents was found tightly fixed to the different components of the seed external covers where it persisted during seedling germination. Contrastingly, sanguinarine contents in cotyledon accounted for the remaining 40 % and it could have been, at least partially, mobilized to the newly formed hypocotyls during emergence from seeds. Berberine was only detected in immature seeds and in seedlings once cotyledons were totally displayed. These results are discussed as a possible sanguinarine role in the chemical protection during seedlings germination. Resumen. Semillas de Argemone mexicana L. acumulan cantidades elevadas de sanguinarina. Un análisis de la distribución de alcaloides en los diferentes tejidos que componen la semilla reveló que hasta un 60 % del contenido se encontraba fuertemente unido en las capas que forman la cubierta exterior, donde se retuvieron durante la emergencia del hipocótilo. En contraste, los cotiledones presentaron el 40 % restante y parte de ello pudo haber sido movilizado al hipocótilo al emerger. Berberina sólo se observó en semillas inmaduras y en plántulas en desarrollo con los cotiledones desplegados. Estos resultados se discuten en función del posible papel defensivo de la sanguinarina durante la germinación.

Seedbank persistence and emergence pattern of Argemone mexicana, Rapistrum rugosum and Sonchus oleraceus in the eastern grain region of Australia

A thorough understanding of the emergence pattern and persistence of weed seeds is a prerequisite in framing appropriate weed management options for noxious weeds. In a study conducted at the University of Queensland, Australia, the emergence and seed persistence behavior of three major weeds Sonchus oleraceous, Rapistrum rugosum, and Argemone mexicana were explored with seeds collected from Gatton and St George, Queensland, Australia, with an average annual rainfall of 760 and 470 mm, respectively. Seed persistence was evaluated by placing seeds at the surface layer (0 cm) or buried at 2 and 10 cm depths enclosed in nylon mesh bags and examined their viability for 42 months. In another study, the emergence pattern of four populations, each from these two locations, was evaluated under a rainfed environment in trays. In the mesh-bag study, rapid depletion of seed viability of S. oleraceous from the surface layer (within 18 months) and lack of seed persistence beyond two years from 2 and 10 cm depths were observed. In trays, S. oleraceous germinated 3 months after seeding in response to summer rains and there was progressive germination throughout the winter season reaching cumulative germination ranging from 22 to 29% for all the populations. In the mesh-bag study, it took about 30 months for the viability of seeds of R. rugosum to deplete at the surface layer and a proportion of seeds (5 to 13%) remained viable at 2 and 10 cm depths even at 42 months. Although fresh seeds of R. rugosum exhibit dormancy imposed due to the hard seed coat, a proportion of seeds germinated during the summer months in response to summer rains. Rapid loss of seed viability was observed for A. mexicana from the surface layer; however, more than 30% of the seeds were persistent at 2 and 10 cm depths at 42 months. Notably, poor emergence was observed for A. mexicana in trays and that was mostly confined to the winter season.