Stimulation of Root Growth of Several Vegetables by Extracts from a Commercial Preparation of Agar

Abstract

Commercial preparations of agar, agarose, cellulose, gellan gum, pectin, sodium alginate, and starch were immersed in water and assayed for root growth-promoting activity. Agar greatly stimulated root growth of cucumber (Cucumis sativus L.), Japanese radish (Raphanus sativus L.), lettuce (Lactuca sativa L.), rice (Oryza sativa L.), spinach (Spinacia oleracea L.), tomato (Lycopersicon esculentum Mill.), and Welsh onion (Allium fistulosum L.). Cellulose, gellan gum, and starch also stimulated root growth to a lesser degree. The most consistent results were obtained with lettuce; thus it was chosen for further experimentations. Water extract of agar stimulated root growth of lettuce whereas an inorganic ion solution whose composition was equivalent to the agar extract was less stimulating. Thus, the stimulating activity of the agar extract is not attributable to inorganic ions in the extract. To examine properties of root growth-stimulating substances in the agar extract, the extract was fractionated on columns of Sephadex G-25, Bio-Gel P-2 and Shodex C18. Activities were found in several low molecular weight fractions isolated with Bio-Gel P-2. When the active fractions separated by Bio-Gel P-2 were subjected to Shodex C18, an active fraction was concentrated in a single major peak, which eluted faster than glucose. These results indicate that commercial preparations of agar contain several root growth-stimulating, highly hydrophilic substances of low molecular weight.