Stem - Plant Growth Substances

The role of auxins, cytokinins, ethylene and abscisic acid in controlling the apical bud dominance and lateral bud dormancy (Apical Dominance) are discussed earlier. Auxins also play a role in phototropism, geotropism and other responses of stems. Auxin-cytokinin interaction regulates the differentiation and growth of shoots from callus. Gibberellins stimulate cell division and cell elongation in shoot apices. Gibberellins abolish the dwarfism (rossette conditions) in plants and promote stem elongation.