Crotonic acid as a bioactive factor in carrot seeds (Daucus carota L.) Izabela Jasicka-Misiak * , Piotr P. Wieczorek, Paweł Kafarski Institute of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland Received 8 November 2004; received in revised form 1 April 2005 Available online 10 May 2005 Abstract Water extracts from the carrot seed (Daucus carota L.) var. Perfekcja exhibit plant growth inhibitory properties against cress, cucumber, onion and carrot in a dose-dependant manner. This property results from the action of low-and high-molecular compo- nents of the extract. The low-molecular component was identified as crotonic acid ((E)-2-butenoic acid). Its presence was also con- firmed in other late varieties of carrot. The determined strong herbicidal properties of crotonic acid and its availability after release to soil combined with its high level in seeds suggest that it might be considered as an allelopathic and autotoxic factor in the seeds. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Daucus carota; Umbelliferae; Allelopathy; Autotoxic activity; Herbicidal activity; Crotonic acid 1. Introduction Plants are known to produce secondary metabolites that affect germination and growth of other plants. This is one of a variety of ways in which certain plant can re- duce interspecies competition in their natural habitats. Some of these compounds may play an important role in chemical mediation of growth and development of natural plant communities (Dayan et al., 2000; Duke et al., 2000a,b, 2002; Seigler, 1996; Vyvyan, 2002). Over many years, various types of allelochemicals have been isolated and characterised from a vast num- ber of plants and their organs (Chaves et al., 2001; Hase- gawa et al., 1992; Macias et al., 1998, 1999; Ohno et al., 2001; Rice, 1984; Rizvi and Rizvi, 1992). Chemical inter- ference is one of various stresses, which plants must cope with in nature, and therefore it has been studied quite intensively. Allelochemic natural products have been implicated in the patterning of vegetation and weed growth in agricultural systems. It has been also sug- gested that the release of allelochemicals to the environ- ment may decrease crop yields. Alternatively, these allelochemicals offer a potential as natural herbicides since such compounds constitute standard chemical weapons not only of toxic plants but also common veg- etables (Casini and Olivero, 2001; De Feo et al., 1997; Vaughn and Berhow, 1998; Yu and Matsui, 1994). Carrot (Daucus carota L.) is a very popular vegetable cultivated world-wide and popularly used for culinary and cosmetic purposes. Various parts of the plant have also been therapeutically used in folk medicine; e.g. car- rot leaves are good diuretics, the seeds are also diuretic and carminative are used for treatment of hangovers, and to stimulate menstruation. The results of our preliminary study have shown that the spectrum of weeds in carrot cultivars in the rural re- gion of Opole (southwestern part of Poland) is limited to 12 species from among 100 weeds commonly observed in this area. Although carrot is accompanied by a limited number of weeds, the information about its alle- lochemicals is scarce, with exception of reports concern- ing carrot–insect interactions (Cole, 1985; Degen et al., 1999a,b; Guerin et al., 1983; Guerin and Sta ¨dler, 1984). Additionally, it is well established that too dense sowing of carrot seeds results in delay and inhibition of 0031-9422/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.phytochem.2005.04.005 * Corresponding author. Tel.: +48 77 4545841; fax: +48 77 4410740. E-mail address: izajm@uni.opole.pl (I. Jasicka-Misiak). www.elsevier.com/locate/phytochem Phytochemistry 66 (2005) 1485–1491 PHYTOCHEMISTRY