ABSTRACT
This chapter presents the first evidence that ethylene was not only an inhibitor of elongation in land plants, but could actually stimulate elongation growth, at least in rice. It discusses the reliability of ethylene as an internal signal for submergence in relation to fast shoot extension in habitats differing in their oxygen concentration. Plant hormones involved in stimulating shoot extension do not operate by themselves, but interact with other plant hormones and also with atmospheric gases. These interactions or their absence will be discussed in for mechanisms of shoot elongation that are driven either by ethylene or by carbon dioxide. The only example of a plant species with a submergence-induced elongation response driven by carbon dioxide and anoxia, but not ethylene, is Potamogeton pectinatus. Under certain environmental conditions, enhanced shoot elongation decreases, rather than increases plant survival.
