Proteoid Roots. Physiology and Development

Abstract

Nearly 100 years ago, Engler described the unusual root morphology of plants in the family Proteaceae growing in the Leipzig Botanic Gardens. They had extensively branched roots covered with long, densely grouped absorption hairs. It wasn't until 1960 that Purnell coined the term “proteoid root” to describe a root with “dense clusters of rootlets of limited growth.” She examined 44 species from 10 genera in the family Proteaceae and observed proteoid roots in all but the more primitive genus Persoonia. Subsequent surveys have documented proteoid roots in 27 genera of Proteaceae (Dinkelaker et al., 1995). Proteaceae are a major component of the Mediterranean flora of southwestern Australia and South Africa, where nutrient-impoverished soils support an amazing diversity of plant species. Purnell (1960) suggested that proteoid roots were involved in nutrient uptake because they had proliferated in a layer of blood and bone manure placed in an otherwise nutrient-poor sand. Proteoid roots have now been reported in 28 species from the Betulaceae, Casuarinaceae, Eleagnaceae, Leguminosae, Moraceae, and Myricaceae families, all of which can symbiotically fix atmospheric N2, apart from Ficus benjamina and members of the Proteaceae. Clusters of swollen, short, lateral roots occur in species of the Cyperaceae and Restionaceae, and their overall morphology is similar to proteoid roots; however, to date nothing is known of their physiology (Dinkelaker et al., 1995).