Root hair uptake

Polyvinyl chloride cylinders -1- nylon gauze -1- device for continuous water supply Soil slices at measurable distance from soil-root interface. High bulk density of soil sampled. Nutrient uptake through an induced root hairs surface. Study of rhizosphere effect over a time and distance gradient from the soil-root interface. 47, 67, 127-129... 

The classic Barber-Cushman model treats the root surface as a smooth solid cylinder. Yet many experimental studies have shown that root hairs are important for the uptake of some nutrients, e.g., P (25,26). Various mathematical models for root hairs have been used (5,27,28), which all differ slightly in the way in which root hairs are modeled. Most authors conclude that root hairs make a substantial contribution to uptake, particularly for relatively immobile nutrients. 

T. S. Gahoonia and N. E. Nielsen, Variation in root hairs of barley cultivars doubled soil phosphorus uptake. Euphytica 98 11 (1997). 

S. Itoh and S. A. Barber. A numerical solution of whole plant uptake for soil-root uptake including root hairs. Plant Soil 70 403 (1983). 

J. S. Gcelhoed. L. J. M. Sipko, and G. R. Findernegg, Modelling zero sink nutrient uptake by roots with root hairs from. soil compari.son of two models. Soil Sci. 162 544 (1997). 

Also, Schmidt et al. (2005) found a significant increase in root hair density by working with Arabidopsis thaliana, which were treated with water extractable humic substances (WEHS), suggesting that these substances induce a nutrient acquisition response that favors the uptake of nutrients via an increase in the absorptive surface area. Furthermore, a phenotypical analysis of an array of mutants harbouring defects in root epidermal patterning revealed that root hair density of the ttg and gl2 mutants, defective in cell specification, was significantly modified, indicating an effect at/or downstream of the determination of the cells. 

Figure 9.3. Model for the action of humic substances (HS) on plasma membrane-bound targets of a root hair cell. Besides the well-known effects on plasma membrane H+-ATPase (P) and carriers (C) of mineral nutrients, the envisaged alteration of membrane lipid environment and the possible interaction with an hypothetical membrane receptor (R) for humic molecules which allows transduction of the signal for induction and expression of genes involved in nutrient uptake and root hair development are also presented.

Transverse section of a typical root. ° The complex features of the root hair surface that regulate reductase and other activities in metal uptake are only beginning to be understood. 

Ma JF, Goto S, Tamai K and Ighii M (2001a) Role of root hairs and lateral roots in silicon uptake by rice. Plant Physiol 127 1773-1780. 

The mycelia of the ectotrophic mycorrhiza often largely replace the root hairs and seem to act as their substitute in nutrient uptake. Our knowledge of how mycorrhiza function is inadequate, and the exact mechanisms by which the fungi benefit their host are largely unknown (see Chapter 5 and 28). 

Among the first to consider root hairs in their model were Bhat et al. (1976) and Itoh and Barber (1983), while attempting to explain experimentally obtained P uptake values exceeding those calculated by one of the previously available models. Three principal approaches to integrate root hairs into a rhizosphere model are found in the literature (1) The boundary where exudation and uptake occurs is extended by the length of the root hairs (e.g. Kirk, 1999) (2) The continuity equation for root uptake is extended with a separate sink term (e.g. Geelhoed et al., 1997) and (3) The transport equation is solved in a three-dimensional model with cylindrical coordinates (Geelhoed et al., 1997). 

Uptake properties as for the root itself. The uptake hy root hairs was introduced hy the addition of a sink term into Model 1. The resulting set of equations is presented in Table 3. 

Transport parameters, sorption parameters, including the composite Freundlich sorption isotherm, initial pool sizes, root uptake kinetics as well as root hair parameters were measured for the experimental conditions of the... 

Geelhoed, J.S., Mous, S.L.J., Findenegg, G.R., 1997. Modehng zero sink nutrient uptake by roots with root hairs from soil comparison of two models. Sod Sci. 162, 544—553. 

Itoh, S., Barber, S.A., 1983. Phosphorus uptake by six plant species as related to root hairs. Agron. J. 75, 457 61. 

Acid rain dams es trees in several ways. It disturbs the stomata (openings) in tree leaves and causes increased transpiration and a water deficit in the tree. The surface structures of the bark and the leaves can also be destroyed by the acid. Acid rainfall can acidify the soil, damaging fine root hairs and thus diminishing nutrient and water uptake. In addition, acid rain dissolves minerals that are insoluble in groundwater and surface waters of normal pH, and many of these minerals contain metal ions toxic to plant life. For example, acid rain dissolves aluminum hydroxide in the soil, allowing aluminum ions (Al ) to be taken up by the roots of plants, where they have toxic effects. 

Root hairs (Fig. 1.4) are very small white, hair-like structures that are found near the tips of all roots. As the root grows, the hairs on the older parts die off and others develop on the younger parts of the root. They play a very important part in the nutrition and water uptake of a plant. 

Fig. 5.8. Distributions of different elements in a human hair strand (with root) obtained with the PIXE microbeain technique. The beard hair belonged to the famous astronomer Tycho Brahe (1546-1601), and was retreaved at a tomb opening. Note the uptake of mercury shortly before the death of the bearer [5.14]...

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