Evidence for the Uptake of Non-Essential Ions and Essential Nutrient Ions by Root Hairs and Their Effect on Root Hair Development

Abstract

Root hairs are tubular extensions of epidermal cells found on roots of most vascular plant species (Cormack 1962; Hofer 1991; Peterson and Farquhar 1996). There has been considerable debate as to the role of root hairs in nutrient uptake and observations of the normal growth of shoots of two of three root hair mutant lines of Zea mays L. (maize) suggest that they may not always play a significant role (Wen and Schnable 1994). Root hairs when present, however, extend the absorbing surface of roots and therefore presumably affect the uptake of nutrients in the vicinity of the root cylinder (Jungk 1991). Clarkson (1991) argues that if the density of root hairs is great enough, the depletion zones of adjacent hairs will overlap thus most available ions in the soil nutrient solution between adjacent root hairs will be available for uptake. The distance away from the depletion zone surrounding the root cylinder to which root hairs elongate extends the region of the rhizosphere from which nutrients can be absorbed (Nye 1966; and Fig. 1). There has been some interest, therefore, in using genotypes of agricultural species with long root hairs to enhance nutrient uptake. This characteristic, as well as the ability of root hairs to grow into small soil pores and into soil particles, could positively affect nutrient uptake. This would be of particular importance in terms of ions such as phosphate that are bound to soil fractions and are essentially immobile (Jungk 1991).