Responses of Elodea densa to Growth-Regulating Substances

Abstract

Studies were made of the responses of excised bud-nodes and apical segments of Elodea densa plants to treatment with some 16 growth substances and related compounds at cones, generally from 1 to 5 ppm. These segments were grown directly in solutions of the growth substances in 250 ml. glass tumblers[long dash]the source of light being the daylight type fluorescent for 13 hrs. each day. The principal responses included shoot growth, the number of roots emerging, the time and order of their appearance, their lengths, and root hair development. The bud node of the primary axis was shown to have 4 root primordia in several specific regions. These primordia remain latent until the bud nodes are excised or other injury occurs. The roots can readily be measured since the roots are unbranched, and 4 is the max. number developing for each bud node. In the control cultures root hairs were rarely formed on the free-growing roots. Root-hair development did occur upon treatment with certain types of compounds[long dash]those with the indole or naphthalene ring system containing side chains with actual or potential acid groups. The root-hair forming substances included indoleacetic, indolepropionic, indolebutyric, naphthalene-acetic, naphthalene acetamide, and 1-tryptophane. In cultures of indolepropionic at 5 ppm. structural abnormalities developed in the terminal portions of the root-hair cells. In view of the specificity of the root-hair test it may be useful in establishing diagnostic characters for the classification of certain of the growth-regulating substances. Under suitable growing conditions these bud-nodes were capable of developing into complete new plants[long dash]a reasonably good growth being maintained at an intensity of about 400 f.c. At the low intensity of 200 f.c. responses to indolepropionic were noted at a cone, of 104 g./l. Increased growth was also associated with histidine and indolebutyric acid in cultures at low light intensities. The association of the growth substances with the enzymatic processes, with the synthesis of total solids, and with salt absorption and water regulation were considered in relation to this stimulation.