Pattern formation in cluster roots: Some developmental and evolutionary considerations

Cluster roots, also known as proteoid roots, are one of the major adaptations for nutrient acquisition in terrestrial vascular sporophytes, occurring in many important plant families, in key areas of biodiversity, and in significant ecological niches. Their development and function are closely linked and present an ideal experimental system with which to investigate the basis of pattern and its morphogenetic amplification. Both meristem function and root initiation are controlled within a spatial and temporal framework, resulting in predictive phenotypic expression. In this paper, these patterns of development are described within the context of our knowledge of lateral root initiation and development. Recent work is summarized in an attempt to highlight the issues of most importance for future research. The case of the genus Lupinus is taken as a means of exploring the phylogenetic relationships of species with cluster roots. The first evidence of cluster roots having arisen only once within the Lupinus genus is presented. (C) 2000 Annals of Botany Company.