Plant movement; kinetics and hormonal regulation of hyponastic growth and petiole elongation

The experiments described in this thesis have shown that the plant hormones ethylene, auxin, abscisic acid (ABA) and gibberellins (GAs) play roles in the regulation of hyponastic growth of R. palustris petioles under water (Chapter 3). This same set of hormones is also important for non-differential stimulated elongation of the petiole upon submergence (Chapter 4). These two submergence-induced growth processes are linked; petiole elongation can only start to take place when the petiole has reached a certain threshold angle via the process of hyponastic growth (Chapter 2). A model is proposed that describes the hormonal regulation of both growth processes, and the interaction between hyponastic growth and stimulated elongation of R. palustris petioles under water. We have also shown that A. thaliana is a good model species to study the hormonal regulation of hyponastic growth in more detail (Chapter 5, 6). The hyponastic response in this species seems to be very similar to that of R. palustris, and the availability of a large number of hormone mutants in A. thaliana provides a unique opportunity to examine the involvement of plant hormone signal transduction components. These studies have shown that both R. palustris and A. thaliana possess signal transduction pathways to perform hyponastic growth and petiole elongation. However, differences exist between species and accessions in the signals that are able to switch on these growth responses