This lecture is about specific effects of two groups of plant hormones: cytokinins, and ethylene. The main effects of cytokinins are stimulation of cell proliferation, and stimulation of growth of shoots from undifferentiated tissue (callus) in plant tissue culture. Together with auxins, cytokinins regulate apical dominance which determines the growth pattern of plants. Ethylene is a gas and as such diffuses very easily and quickly. In climacteric fruits like banana or tomato ethylene accelerates the ripening process, and promotes leaf fall and fruit fall (abscission). We also have a look at a couple of mutations called SNORKEL in rice that cause very rapid and extreme elongation of the stem internodes. Copyright 2012 La Trobe University, all rights reserved. Contact for permissions.