Elongation Growth of Setae of Pellia (Bryophyta): Effects of Auxin and Inhibitors

Abstract

Summary Growth of setae of the liverwort, Pellia epiphylla, was monitored with intact plants and with excised stalks in aqueous solutions. Growth of sporangiophores of intact plants was linear for nearly 48 hours at an average rate of about 0.6 mm/h. Excised setae in the presence of a near optimal concentration of 0.1 mM indole-3-acetic acid (auxin) grew at a steady-state rate of 0.7-1.2 mm/h, greater than that of the sporangiophores of the intact plant. Elongation was not a simple passive phenomenon since growth of excised setae was inhibited by cycloheximide, puromycin, fluorophenylalanine, anti auxins, coumarin, and heavy water as well as ionophores. Colchicine inhibited auxin-induced but not basal elongation as did the cellulose synthesis inhibitor dichlobenil. Both basal and auxin-induced elongation were sensitive to cytochalasin B. The inhibitory effects of cytochalasin B are obvious only in short pieces of setae. As shown by the application of radioactive cytochalasin B, this is due to its poor penetration. The results are significant in that they demonstrate an example of auxin-promoted elongation where the rate of growth of excised setae equals or exceeds that of the intact plant and is clearly not an example of a passive thinning of auxin-loosened walls. Rather growth is dependent upon maintenance of organized structure and macromolecule synthesis.