THE EFFECTS OF ETHIONINE ON SOME PLANT GROWTH SYSTEMS

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Abstract
Ethionine (CH3∙CH2∙S∙CH2∙CH2∙CH∙NH2COOH) was tested on six plant growth systems: (a) growth of lateral buds on decapitated dwarf beans, (b) rooting of excised, etiolated bean hypocotyls, (c) linear growth and final cell size of primary roots of wheat, (d) growth of hypocotyl and roots of flax seedlings, (e) growth of sections from etiolated pea shoots, and (f) expansion of leaf disks from etiolated beans. Ethionine stimulated growth in each of these systems with the possible exception of (a) and (d). The work on the rooting of etiolated bean hypocotyls includes the description of a new rooting test.Pretreatment of pea sections with manganese lowered or prevented the stimulatory effect of ethionine.Expansion of etiolated bean leaf disks was not increased by ethylenediaminetetraacetic acid, penicillin G, and the ‘antiauxins’ α (2,4-dichlorophenoxy)- isobutyric acid, α(p-chlorophenoxy)isobutyric acid, and 2,3,5-tri-iodobenzoic acid whereas maleic hydrazide, o-chlorophenoxyisobutyric acid, m-methyl phenoxyacetic acid, and 2,4,6-trichlorophenoxyacetic acid (TCPAA) stimulated expansion. TCPAA, at 10 mg/liter, completely replaced the stimulatory effect of cobalt on light-treated disks. The peculiar dose–response curve and some morphogenetic effects with TCPAA are described.Ethionine, cobalt, and TCPAA all inhibit chlorophyll synthesis in leaf disks exposed to light. TCPAA also causes a loss of yellow pigment in disks kept in the dark.Depending upon the test system, ethionine simulates the effects of auxin or ‘antiauxins’. Metabolic studies with ethionine are briefly reviewed. Some connections between the known effects of ethionine and theories of auxin action, and the possible significance of ethionine as an inhibitor of adaptive enzyme synthesis, are pointed out.