Figure 7.

Simple general model for the effect of elevated IAA on growth of expanding leaf blades of Arabidopsis. The results presented here suggest that IAA applied to leaf blade tissues initiates two signal transduction pathways. Binding of IAA to an undetermined receptor (or receptors) might initiate separate signal transduction events leading in one case to decreased leaf cell expansion (A) or to increased leaf blade cell expansion (B). Since decreased leaf growth results from IAA treatment when leaves either remained attached to the plant or when the leaf blade tissue is unwounded, pathway A would appear to branch through two parallel sub-pathways (A1 and A2). A1 is induced in some fashion by leaf attachment possible due to provision to the leaf of a root derived factor. A2 is inhibited in some fashion by leaf wounding possibly involving wound-induced factors. Pathway B leading to increased leaf blade expansion appears to be upregulated by wounding possibly through wound-induced factors and downregulated by leaf attachment possibly through removal of a root derived factor.