A sizeable minority of taxa is successful in areas prone to submergence. Many such plants elongate with increased vigour when underwater. This helps to restore contact with the aerial environment by shortening the duration of inundation. Poorly adapted species are usually incapable of this underwater escape. | ). It encapsulates much of what was previously discovered for the overall petiole elongation response based on a similar range of experiments incorporating elements of ‘Duplication’; ‘Correlation’; ‘Deletion and re-instatement’; ‘Relevance to lower levels of organization’. They show the process is largely instigated by ethylene (although a small part of the response may have some other cause), to require a decline in endogenous ABA to unblock the ethylene response, and to incorporate an element of GA dependency, but with little evidence for the involvement of expansins. Auxin plays an important role. Removing its presumed source by excising the leaf lamina, lowers IAA concentrations in the petiole and interferes in the hyponasty. At the petiole base, IAA becomes internally redistributed towards hyponasting cells. This redistribution is probably brought about by gravity-stimulated efflux carriers because application of naphthylphtalamic acid, an inhibitor of auxin efflux, suppresses both the redistribution and the hyponastic growth (
