Influence of leaf age on responsiveness of Potamogeton nodosus to ABA-induced heterophylly

The heterophyllous aquatic angiosperm, Potamogeton nodosus, produces morphologically distinct leaves above and beneath the surface of the water. Application of abscisic acid induced entirely submerged plants to produce leaves normally formed at the water surface. A 1 µM application of abscisic acid for 4 h was effective in inducing these developmental changes. There was a window of responsiveness to ABA in that changes in leaf morphology were evident within 2 to 3 days after the treatment and continued for only 4 to 5 days. In addition, only leaves that emerged subsequent to the ABA application developed stomata. This pattern was repeated consistently in plants of different age indicating that leaf age and not plant age was the determining factor in this response to ABA.