Angelicin as the principal allelochemical in Heracleum sosnowskyi fruit.

Distribution patterns of furocoumarins in fruits of the invasive species Heracleum sosnowskyi Manden. (Sosnowskyi's hogweed) during a cold stratification period were investigated. Angelicin, bergapten, methoxalen and imperatorin were mainly localized in the fruit coats and their content varied depending on the fruit source. Cold stratification treatment (90 days, 2-3 degrees C) reduced the content of furocoumarins in the fruit coats by more than two times, compared with those before stratification. The specific activity of the detected furocoumarins and total activity of crude extracts were evaluated using Lactuca sativa, as acceptor plant. Crude extracts obtained from fruit coats and seeds of H. sosnowskyi suppressed 50% of radicle and hypocotyl growth of lettuce seedlings at the concentration range of 1.0-1.7 mg/mL. The inhibitory activity of angelicin was proved to be the highest compared with the other tested furocoumarins, and the inhibitory activity of crude extracts could be explained mainly by the presence of angelicin. Both, monocots (Lolium multiflorum, Phleum pratensis, Festuca pratesis, Lolium perenne) and dicots (Tripholium repens, Trifolium pretense) were found to be sensitive to the exudates of whole H. sosnowskyi fruits. Thus, we assume, that high inhibitory potential of furocoumarins, especially angelicin, at high seed productivity of H. sosnowskyi might have an ecological significance in plant-plant interaction.

Identification of octanal as plant growth inhibitory volatile compound released from Heracleum sosnowskyi fruit.

Heracleum sosnowskyi Manden of the Apiaceae family is a malignant invasive plant in Eastern Europe, Belarus and Russia. The species is known for its prolific seed production, which has been linked to the plant's invasive success. The fruit also has a strong aroma, but the contribution of the fruit's volatile constituent to out-compete neighboring plants has not been fully established. In this study, fruit volatiles of H. sosnowskyi and conspecifics (i.e. H. asperum, H. lescovii, H. dissectum, H. hirtum) were identified by headspace gas chromatography-mass spectrometry (HS-GC-MS). Octyl acetate, octanol, octanal, hexyl isobutyrate, and hexyl-2-methyl butyrate were found to be the principal volatiles. Using authentic standards, the growth-inhibitory property of the individual compounds was assayed by the novel Cotton swab method. Assay results with lettuce (Lactuca sativa) showed that octanal strongly inhibited seed germination and radicle elongation of seedlings. The results suggest that octanal may be the main contributor to the allelopathic activity of H. sosnowksyi fruits. Furthermore, the mixture of fruit volatiles from the invasive H. sosnowskyi more strongly delayed lettuce seedling elongation than the volatiles from fruits of the non-invasive H. asperum, H. lescovii, H. dissectum and H. hirtum. Thus, the present study is the first to demonstrate the possible involvement of fruit volatiles of Heracleum species in plant-plant interaction.