Abstract
In some previous studies, we described the isolation of nine compounds from leaves of Derris urucu, a species found widely in the Amazon rainforest, identified as five stilbenes and four dihydroflavonols. In this work, three of these dihydroflavonols [urucuol A (1), urucuol B (2) and isotirumalin (3)] were evaluated to identify their potential as allelochemicals, and we are also reporting the isolation and structural determination of a new flavonoid [5,3'-dihydroxy-4'-methoxy-(7,6:5″,6″)-2″,2″-dimethylpyranoflavanone (4)]. We investigated the effects of the dihydroflavonols 1-3 on seed germination and radicle and hypocotyl growth of the weed Mimosa pudica, using solutions at 150 mg.L-1. Urucuol B, alone, was the substance with the greatest potential to inhibit seed germination (26%), while isotirumalin showed greater ability to reduce the development of the hypocotyl (25%), but none of the three substances showed the potential to inhibit radicle. When combined in pairs, the substances showed synergism for the development of root and hypocotyl and effects on seed germination that could be attributed to antagonism. When tested separately, the trend has become more intense effects on seed germination, while for the substances tested in pairs, the intensity of the effect was greater on development of weed.
Highlights
Over the past few decades, in order to meet a growing demand for food, the so-called modern agriculture has been increasingly dependent on agrochemicals, such as fertilizers, and specially, agri cultural defensives
Several chemical prospecting studies of this plant have been more restricted to its roots, being identified the presence of rotenoids rotenone, deguelin, tefrosin and rotenolone as major metabolites and minor compounds belonging to the flavanone, isoflavanone, chalcone, flavonol, pterocarpan, stilbene and saponin classes (Braz Filho et al 1975, Parente and Mors 1980, Fang and Casida 1999, Pereira et al 2000)
Some information is found in the literature indicating this activity for different compounds of flavonoids (Anaya et al 2003, Tseng et al 2003, Perry et al 2007, Simões et al 2008)
Summary
Over the past few decades, in order to meet a growing demand for food, the so-called modern agriculture has been increasingly dependent on agrochemicals, such as fertilizers, and specially, agri cultural defensives. In tropical regions, such as the Amazon, those needs are more present mainly due to acid soil conditions and low natural fertility, and Chemical substances produced by the plants themselves have been one of the many viable alternatives to face such issues. Like herbicides many of these substances act in the plant metabolism, a potential replacement to synthetic products available in the market (Duke et al 2002) Another favorable topic is the similarity of molecular sites of action between natural products and synthetic products (Duke and Abbas 1995). As a result, during the last few years several studies have been conducted with native plants from the Amazon which have helped to identify powerful allelochemicals for possible agricultural use (Arruda et al 2005, Souza Filho et al 2005, 2006a, 2009, Santos et al 2007, Lôbo et al 2008, Vilhena et al 2009)
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