Three polyacetylenes, 8-(beta-D-glucopyranosyloxy)-3-hydroxy-1,9,14-pentadecatriene-4,6-diyne, termed "helian"(1), 8-acetoxy-3-hydroxy-1,9,14-pentadecatriene-4,6-diyne (2), and 3,8-dihydroxy-1,9,14-pentadecatriene-4,6-diyne (3) were isolated from seedlings of sunflower, Helianthus annuus L. cv Russia. Compounds 1 and 2, having a beta-glucose and an acetoxy group at C-8, respectively, showed a weak effect on the growth of roots and shoots of rice (Oryza sativa L.) and cress (Lepidium sativum L.), while compound 3, having a free hydroxyl group at C-8, exhibited a growth promoting effect on the roots and shoots of rice and cress.