Specificity of Nicotinic Acid as a Growth Factor for Isolated Pea Roots.

It is known that nicotinic acid is essential to the growth of numerous species of isolated roots (ADDICOTT and BONNER, 1, BONNER and DEVIRIAN, 4). The present paper is concerned with the chemical specificity of nicotinic acid as a root growth factor. Methods The pea roots (variety Perfection) which were used exclusively in the present experiments were cultured according to the methods outlined in earlier papers (BONNER and ADDICOTT, 3; BONNER and DEVIRIAN, 4). Fourmm. tips were cut from the roots of aseptic pea seedlings and transferred to nutrient medium containing per liter of redistilled water 236 mg. Ca (NO3)2 4H20; 36 mg. MgSO4 7H20; 81 mg. KNO3; 65 mg. KCl; 20 mg. KH2P04; 1.5 mg. ferric tartrate; and 40 gm. of sucrose. After the tips had remained in the medium for one week at 250 C., and had grown into roots several cm. long, they were subcultured by tranferring 1-cm. tips to fresh nutrient solution. This process of subculture was repeated weekly. Vitamin B1, which is essential to the continued growth of isolated pea roots, was added at the rate of 0.1 mg. per liter to all of the nutrient solution for transfers later than the first. Nicotinic acid, or related substance to be tested for ability to replace nicotinic acid, was added at the rate of 0.5 mg. per liter, sinee this concentration has been found to be approximately optimal for pea roots (ADDICOTT and DEVIRIAN, 2). A rigid selection for uniformity in root growth rate was carried out at the end of the first week of culture in order to assure the greatest possible uniformity in the roots actually used in each experiment. In a single experiment 400-500 roots were cultured and 20-50 roots were used for testing the activity of each substance reported below. In each experiment the roots were maintained through 5 or more weekly transfers.