Root hair development

T. Beguiristain and F. Lapeyrie, Host plant stimulates hypaphorine accumulation in Pisolithus tinctorius hyphae during ectomycorrhizal infection while excreted fungal hypaphorine controls root hair development. New Phytol. 136 525 (1997). 

Affects root and root hair development and shoot growth... 

Other evidence on morphological modifications attributed to HS treatment concern root hair development. In this sense, Concheri et al. (1994) identified a strong proliferation of root hairs compared to control plants in wheat root supplemented with HS up to a concentration of lOmgC liter-1, with best results for HMS and LMS obtained with 5 and O.lmgCliter-1, respectively. 

Schmidt, W., Cesco, S., Santi, S., Pinton, R., and Varanini, Z. (2005). Water-extractable humic substances as nutrient acquisition signals for root hairs development in Arabidopsis. In Rizosphere 2004—Perspectives and Challenges,Hartmann, A., Schmid, M., Wenzel, W., and Hinnsinger, P., eds., GSF-Berich, Neuherberg, p. 71. 

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.

Through screening of high and low mutant oil lines of Arabidopsis, Shen et al. (2006) discovered that a knockout of homeobox gene GLABRA2 resulted in a high-oil phenotype. GLABRA2 encodes a transcription factor required for normal trichome and root hair development. The mechanism by which this transcription factor affects seed oil accumulation is not known. 

Yang, X. et al. (2004) Manipulation of root hair development and sorgoleone production in sorghum seedlings. J. Chem. Ecol. 30, 199-213... 

Wymer, C. L., Bibikova, T. N. and Gilroy, S. (1997). Cytoplasmic free calcium distributions during the development of root hairs of Arabidopsis thaliana. Plant J. 12, 427-39. 

Studies on the white clover -Rhizobium trifolii interaction are the most advanced. Trifoliin A, a lectin present in clover-seedling roots, binds hapten reversibly to carbohydrate antigens cross-reactive on the capsular polysaccharide of R. trifolii and clover epidermal-cells.244 A specific hapten that inhibits binding of trifoliin A to both surfaces is 2-deoxy-D-arabino-hexose.245 It has also been shown that levels of trifoliin A on root hairs decline with increasing concentrations of nitrate, in parallel to root-nodule development,246 and that lectin receptors are transient on R. trifolii, in a way coinciding with its capacity to be adsorbed to clover roots.247... 

In the last 40 years of research on HS biological activity, several aspects have been elucidated. The favorable morphological effects of HS on plants regarding growth enhancement have been demonstrated on several plant species under different study conditions. Besides these observations, effects on morphogenesis have also been demonstrated in terms of (a) the induction of lateral root formation and (b) root hair initiation and development in intact plants and stimulation of root and shoot development in treated cell calluses. 

One of the most important features in the soil-plant relationship is the rhizosphere extent. This factor is highly variable, ranging from <1 mm to several millimeters and strongly dependent on the gradients that develop in the rhizosphere as a consequence of different processes. In these processes a crucial role is played by the root hairs, tubular outgrowths of root epidermal cells the development of root hairs is dependent on the genotype and is affected by the environmental conditions (e.g. nutrient availability, abiotic stresses and hormones). 

The Rhizobium occurs in specialized nodules on the roots of the legumes. These are developed when the soildwelling Rhizobium invades a root hair, stimulating the plant to form a nodule. Nodule development is inhibited in acidic soils and if the concentrations of nitrate in soil are large. To protect the nitrogenase enzyme, the interior... 

Developing trees contain two major types of meristems (1) terminal or apical meristems and (2) lateral meristems. Apical meristems are located at the tips of all stems and branches (both termed shoots) where they are contained within terminal buds they are also located within the tip regions of all roots. In the tip regions, the meristematic zone is usually protected by another zone of cells called the root cap. Root hairs, or microscopic roots, have no apical meristems, but these minute structures are lateral projections of roots that do have apical meristems. 

Certain bacteria have developed methods for fixing nitrogen. These bacteria live on the root hairs of plants. They take nittogen out of air dissolved in the ground and convert it to compounds, such as nitrates. Those nitrates are used to make protein molecules, compounds vital to the building and growth of cells. 

Gossypol and its methyl ethers (Fig. 1) also are formed in the epidermis and root hairs of the developing seedling root (9) and later are infused throughout the periderm of the root bark of older plants. Terpenoids also are exuded by roots, and exudation is increased by microbial infections (10, 11). Only the root tip is devoid of terpenoids, which may explain wRy this is the only area of the root penetrated by root-knot nematode or fungal wilt pathogens. 

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