Action of Individual Hormones 1. Describe the polar transport system for IAA and explain its significance to the development of the plant. One effect of auxin is to stimulate elongation of coleoptiles and dicot stems in the zone of enlargement. One way in which auxin acts is via acidification of cell walls. Be able to discuss the evidence that supports the acid growth hypothesis for IAA stimulation of wall extensibility.
Gibberellins are a second class of hormones that stimulate plant growth.
Compare auxin-induced growth to gibberellin induced growth including the type of organs stimulated, concentration dependencies, and the nature of the stimulation. Gibberellins also stimulate alpha amylase synthesis is the aleurone layer in cereal grains. How does gibberellin stimulate expression of the amlyase. Describe these hormones and the general effects that these hormones have on development. Ethylene is commerically important in fruit ripening.