Abstract
Ethylene inhibited the growth of sorghum coleoptile and mesocotyl in darkness. It also inhibited the development of mesocotylar roots in darkness. However, ethylene rather stimulated the growth of mesocotyl under red light in a certain range of concentrations, 0.1-10 ppm, although it inhibited the growth of coleoptile and first leaf under the same condition. The optimum concentration of ethylene for mesocotyl growth under the light was different depending on the type of sorghum variety. Ethylene also induced the radial expansion of mesocotyl, especially at concentrations higher than 100 ppm under red light. The volume of mesocotyl increased in all ethylene concentrations tested. Development of mesocotylar roots was rather stimulated by ethylene under red light. Carbon dioxide acted antagonistically with ethylene in the growth of mesocotyl and coleoptile in darkness. Thus, sorghum mesocotyl is a unique organ in which ethylene stimulates not only longitudinal growth but also radial expansion.
