ABSTRACT
Plant growth and development are coordinated by chemicals known as phytohormones. Anton Nicolyovitch Nelubjov (1901) first proposed that ethylene had the capacity to influence plant behavior a century ago, and since that time it has been shown to be responsible for profoundly affecting growth and development, even at concentrations as low as 0.1 µL L−1 (Osborne, 1989). However, unlike the other phytohormones, ethylene is a simple volatile hydrocarbon (C2H4) that is active in the gaseous form. A diverse range of physiological processes are influenced by ethylene. These include the senescence and abscission of leaves and flowers, the ripening of fruit, and the germination of seeds (Abeles et al., 1992). Moreover, dicotyledonous seedlings exposed to ethylene display a characteristic syndrome of responses that are known collectively as the triple response. This diagnostic phenomenon comprises a reduction in stem elongation, an increase in the radial expansion of the stem, and a diagravitropic orientation of the aerial tissues. However, ethylene also plays a fundamental role in coordinating the growth and development of roots. In this chapter the importance of ethylene in the development of root morphology is described, and the role of the gas in the regulation of plant responses to the rooting environment is evaluated. Finally, the exciting opportunities of generating desirable root characteristics by the manipulation of ethylene biosynthesis and/or perception are discussed.
