ON THE INHIBITION OF MESOCOTYL GROWTH BY ETHYLENE

Abstract

SummaryOat seedlings have been treated with ethylene‐generating substances, (2‐chloroethyl)phos‐phonic acid (ethrel) and β‐hydroxyethylhydrazine (B‐OH), as well as with gaseous ethylene in an attempt to confirm the claim that mesocotyl growth can be stimulated by ethylene. The factorially arranged experiments included a standard exposure to light to permit evaluation of the light × ethylene interaction.Ethrel always inhibited growth and caused the malformations associated with ethylene treatment. In contrast, B‐OH brought about the ‘CO2 effect’; that is, mesocotyl growth was retarded at first but subsequently enhanced due to an increased number of cells having an unchanged final length, while the growth of the coleoptile was reduced. These plants showed no ethylene‐type distortions, however. As ethylene gas itself was invariably inhibitory it cannot be assigned any stimulatory properties at the concentrations used.One treatment combination (B‐OH with CO2) caused the death, selectively, of the tip cells of the coleoptile. Even without these cells, allegedly an essential part of the growth‐regulatory system of the seedling, a promotion of mesocotyl growth was observed.In the discussion support is deduced for the view that mesocotyl growth is not controlled by the tip of the coleoptile.