Hatching stimulation activity of steroidal glycoalkaloids toward the potato cyst nematode, Globodera rostochiensis

Cyst nematodes (Globodera spp. and Heterodera spp.) are highly evolved sedentary endoparasites that are considered as harmful pests worldwide. The hatching of the dormant eggs of cyst nematodes occurs in response to hatching factors (HFs), which are compounds that arc secreted from the roots of host plants. Solanocclepin A (SEA), a triterpene compound, has been isolated as HF for potato cyst nematode (PCN) eggs, whereas other compounds, such as steroidal glycoalkaloids (SGAs), arc also known to show weak hatching stimulation (HS) activity. However, the structures of both compounds are different and the HF-mediated hatching mechanism is still largely unknown. In the present study, we observed specific hatching of PCN eggs stimulated by the hairy root culture media of potato and tomato, revealing the biosynthesis and secretion of HFs. SGAs > such as alpha-solanine, alpha-chaconine, and alpha-tomatine, showed significant HS activity, despite being remarkably less activities than that of SEA. Then, we evaluated the contribution of SGAs on the HS activities of the hairy root culture media. The estimated SGAs content in the hairy root culture media were low and nonconcordant with the HS activity of those, suggesting that the HS activity of SGAs did not contribute much. The analysis of structure-activity relationship revealed that the structural requirements of the HS activity of SGAs are dependent on the sugar moieties attached at the C3 hydoroxyl group and the alkaloid property of their aglycones. The stereochemistry in the EF rings of their aglycone also affected the strength of the HS activity.