Gibberellin function in root growth and development

While early research gave ambiguous results as to the requirement of root growth for the growth hormone gibberellin, there is now clear evidence that gibberellin signalling is necessary for root extension by determining the rate of cell division in the meristem and cell expansion in the elongation zone. Furthermore, root growth is autonomous for gibberellins, which are synthesised in the growing tip. Roots require lower gibberellin concentrations for normal growth than do shoots, and the concentration is often saturating. Thus, a general reduction in gibberellin content, for example, under stress, impacts shoot growth more strongly, resulting in growth redistribution. This chapter describes the current information on gibberellin biosynthesis and signal transduction in roots and their regulation by developmental and environmental signals, as well as the root developmental processes to which gibberellins contribute. There have been considerable advances in understanding the involvement of the gibberellin downstream signalling component DELLA in determining root architecture and in mapping the sites of gibberellin biosynthesis and signalling at the cellular level. The involvement of gibberellins in the interaction of roots with the external environment and soil micro-organisms is also discussed.