Horacio HEINZEN, Claudia BARRA. Carlos GARCÍA, Silvina GARCÍA.
Sandra LARRAMENDI, Patrick MOYNA
Cátedra de Farmacognosia y Productos Naturales, Facultad de Química.
Gral.Flores 2124. Montevideo, Uruguay
Epicuticular waxes are the first border between plants and its enviroment. Waxes from the green parts of plants have a variable composition according to climate changes, attack of the vegetal by pests, age and other factors. However, seeds while dormant, cannot accommodate to changing environmental conditions. They must have an array of preformed possibilities to overcome different types of stress and survive. In this report we communicate our findings related to compounds having antifungal and herbicidal activities located in epicuticular waxes from seeds, discussing their ecological role:
We focused our interest in three vegetal species: barley. sunflower and bishop's weed.
5(n)alkylresorcinols are responsible for the in born resistance of barley and wheat seeds against pathogenic fungi. The accumulation of 5(n)alkylresorcinols on barley seeds is strongly dependent with the climate conditions when the seed is formed in the plant. Differences up to 20% in concentration of alkylresorcinols were found between seeds formed either in moist or dry springs.
Although sunflower seeds of three differents varieties showed no resistance against Aspergillus flavus growing over the seed or its epicuticular waxes alone, the fungi was able to biosynthese aflatoxins only over one of the cultivars considered.
Bishop's weed is well known as a phototoxic and toxic plant for cattle and the prescence of coumarins all over the plant precludes the observed alelopathic action. The presence of coumanns in the seedwax allows a slow release of these compounds in the germination media assuring the predominance of the weed.