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Allelopathy of fruits in sunflower (Helianthus annuus L) and Mexican sunflower (Tithonia diversifolia (Hemsl.) A. Gray)

Takako Kato1, Kaori Tomita-Yokotani1, Seiji Kosemura2 and Koji Hasegawa1

1 University of Tsukuba, Japan Email kaboka@sakura.cc.tsukuba.ac.jp
2
Keio University, Japan

Abstract

Allelopathy of fruits of compositae, sunflower (Helianthus annuus L) and Mexican sunflower (Tithonia diversifolia (Hemsl) A. Gray), was studied. In this study, exudates of Mexican sunflower seeds were obtained and applied to plant growth test and a fungal germination test. The ethyl acetate-soluble fraction of exudates from seeds inhibited a fungal germination. Seeds (fruits) in Mexican sunflower had allelopathic activity as in the case of sunflower fruits. Sundiversifolide (4, 15-dinor-3-hydroxy-1(5)-xanthene-12, 8-olide) was isolated in the active fraction from exudates of Mexican sunflower seeds (fruits). These results indicate that the sundiversifolide may have been related to the allelopathic activity as allelochemical in Mexican sunflower seeds (fruits).

Media summary

Allelopathy of fruits in Mexican sunflower (Tithonia diversifolia (Hemsl) A. Gray) and sunflower (Helianthus annuus L) were investigated.

Key Words

Allelopathy, compositae, Mexican sunflower, Sundiversifolide, sunflower.

Introduction

It is well known that a lot of mature compositae plants have allelopathic activity, but allelopathy in seeds (fruits) of those plants has been little known. We have reported that germinating sunflower seeds have species-selective allelopathic function. We have already isolated and identified a substance, 4,15-dinor-3-hydroxy-1(5)-xanthene-12,8-olide (sundiversifolide), as an allelochemical from the exudates of germinating sunflower seeds (fruits) (Ohono et al. 2001). Sundiversifolide is a stereoisomer of diversifolide, which was isolated from the extracts of mature Mexican sunflower leaves (Kuo and Lini 1999). Allelopathy of fruits in Mexican sunflower has not yet been investigated, although it has already reported that Mexican sunflower released allelochemicals in soil and these released substances inhibited the growth of other plants. In this study, exudates of Mexican sunflower seeds were obtained and applied to plant growth test and a fungal germination test. Furthermore, the existence of Sundiversifolide in the exudates of Mexican sunflower seeds (fruits) was analysed.

Methods

Plant and microbe materials

Sunflower (Heliathus annuus L cv. Taiyo) fruits were used as plant materials. Wild type strain of Neurospora crassa 74A obtained from Fungal Genetics Stock Center, University of Kansas Medical Center, Kansas City, was used as test fungus.

Extraction and isolation of sundiversifolide

Exudates from Mexican sunflower seeds incubated for one day were corrected. A part of the exudates were evaporated to dryness in vacuo at 38oC. The concentrates were fractionated into ethyl acetate-soluble and -insoluble fractions. The acetate-soluble fraction was purified by a silica gel Sep-pak cartridge (waters) with n-hexane-ethyl acetate solvent system by increasing the ethyl acetate concentration. The 40-100% fraction was further purified by C18 Sep-pak cartridge (waters) with a water-methanol solvent system by increasing the methanol concentration. The 10-60 % fraction was analysed by HPLC and LC- ESI+ /MS and finally established the presence of sundiversifolide by HPLC retention time and mass spectral fragmentation.

Bioassay

The methods of plant and microbe bioassay were the same as described previously (Ohno 2001, Tomita-Yokkotani 2003)

Results

Allelopathic activity was investigated on the exudate of Mexican sunflower (Tithonia diversifolia (Hemsl) A. Gray) (Figure 2 and 3). The ethyl acetate soluble fraction of exudates from seeds inhibited a fungal germination. Sundiversifolide was identified in the active fraction by LC-ESI+/MS analysis (Figure 4). These results indicate that the sundiversifolide may have been related to the allelopathic activity as allelochemical in Mexican sunflower seeds (fruits).

Figure 1. Chemical structure of sundiversifolide.

Figure 2. Effects of exudates, water soluble and ethylacetate soluble fraction from Mexican sunflower fruits on the growth of cat’s eyes seedlings. Bar indicates average ▒SE.

Figure 3. Effects of exudates, water soluble and ethylacetate soluble fraction from Mexican sunflower on the conidial germination of Neurospora crassa. Bar indicates average ▒SE.

Figure 4. LC-ESI+/MS chromatogram and its mass spectral fragmentation. A: Sundiversifolide and B: Fraction of Sundiversifolide from exudates of Mexican sunflower fruits.

Conclusion

Allelopathy of fruits of sunflower (Helianthus annuus L) and Mexican sunflower (Tithonia diversifolia (Hemsl) A. Gray), was studied. Sundiversifolide (4,15-dinor-3-hydroxy-1 (5)-xanthene-12,8-olide) was isolated in the active fraction from exudates of Mexican sunflower seeds (fruits). Allelopathic activity on the exudate of Mexican sunflower (Tithonia diversifolia (Hemsl) A. Gray). Seeds (fruits) in Mexican sunflower had allelopathic activity as in the case of sunflower fruits.

References

Kuo Y-H and Lini B Y. (1999) A new dinorxanthane and chromne from the root of Tithonia diversifolia. Chem.Pharm. Bull. 47, 428-429.

Ohno S, Tomita-Yokotani K, Suzuki T, Node M, Kosemura S, Yamamura S, and Hasegawa K. (2001) A new species-selective allelopathic substance from germinating sunflower (Helianthus annuus L.) seeds. Phytochemistry 56, 577-581.

Tomita-Yokotani K., Kato T, Parvez M M, Mori Y, Goto N and Hasegawa K. (2003) Approach of allelopathy study with Arabidopsis thaliana (L.) Heynh. and Neurospora crassa. Weed Biol. Manag. 3, 93-97.

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