Growth promotion of rice seedlings by allelopathic polysaccharide from Welsh onion

The underground portion of the Welsh onion (Allium fistulosum) was extracte d and separated into seven fractions to purify allelopathic compounds that were found to promote the growth of rice seedlings (Oryza sativa), The 80% (v/v) ethanol-insoluble fraction of the hot water extract showed the highes t growth-promoting effect. Purification by DEAE-cellulose chromatography ga ve four fractions, AD-1, 2, 3 and 4. AD-3 at 1000 ppm stimulated root and s hoot growth by about 2.4 and 1.5 times over the respective water and sucros e-treated controls. The molecular weight of AD-3 was roughly estimated as 6 30 kDa by gel permeation chromatography. Seventy two percent (by wt.) of AD -3 was a carbohydrate and no proteins were detected. A GC analysis of the n eutral sugar composition revealed the presence of Gal (50.1%), Man (17.9%), Ara (10.4%), Rha (8.8%), Glc (7.2%) and Xyl (5.6%). About 3% (by wt.) of t he total carbohydrate was uronic acid, which was identified as GalU by a GC analysis. The remainder of AD-3 was extracted in ethyl acetate after its h ydrolysis with 2 M HCl. The major component of the ethyl acetate-soluble fr action was identified as unsaturated linear primary alcohols, 1-tetradecano l and 1-octadecanol (16% and 84% by peak areas from GC, respectively) by me ans of NMR and GC-MS. Sole or combined treatment of these alcohols did not affect the growth of rice seedlings. After partial hydrolysis with 0.2 M tr ifluoroacetic acid or by a sodium periodate treatment, the activity of AD-3 had completely disappeared, suggesting that the sugar moiety and/or molecu lar size were important for the activity.