Journal of Experimental Botany, Vol. 51, No. 350, pp. 1531-1542,
September 2000
© 2000 Oxford University Press
Water uptake by roots: effects of water deficit
Lehrstuhl für Pflanzenökologie, Universität Bayreuth, D-95440 Bayreuth, Germany
The variable hydraulic conductivity of roots (Lpr) is explained in terms of a composite transport model. It is shown how the complex, composite anatomical structure of roots results in a composite transport of both water and solutes. In the model, the parallel apoplastic and cell-to-cell (symplastic and transcellular) pathways play an important role as well as the different tissues and structures arranged in series within the root cylinder (epidermis, exodermis, cortex, endodermis, stelar parenchyma). The roles of Casparian bands and suberin lamellae in the root's endo- and exodermis are discussed. Depending on the developmental state of these apoplastic barriers, the overall hydraulic resistance of roots is either more evenly distributed across the root cylinder (young unstressed roots) or is concentrated in certain layers (exo- and endodermis in older stressed roots). The reason for the variability of root Lpr, is that hydraulic forces cause a dominating apoplastic flow of water around protoplasts, even in the endodermis and exodermis. In the absence of transpiration, water flow is osmotic in nature which causes a high resistance as water passes across many membranes on its passage across the root cylinder. The model allows for a high capability of roots to take up water in the presence of high rates of transpiration (high demands for water from the shoot). By contrast, the hydraulic conductance is low, when transpiration is switched off. Overall, this results in a non-linear relationship between water flow and forces (gradients of hydrostatic and osmotic pressure) which is otherwise hard to explain. The model allows for special root characteristics such as a high hydraulic conductivity (water permeability) in the presence of a low permeability of nutrient ions once taken up into the stele by active processes. Low root reflection coefficients are in line with the idea of some apoplastic bypasses for water within the root cylinder. According to the composite transport model, the switch from the hydraulic to the osmotic mode is purely physical. In the presence of heavily suberized roots, the apoplastic component of water flow may be too small. Under these conditions, a regulation of radial water flow by water channels dominates. Since water channels are under metabolic control, this component represents an ‘active’ element of regulation. Composite transport allows for an optimization of the water balance of the shoot in addition to the well-known phenomena involved in the regulation of water flow (gas exchange) across stomata. The model is employed to explain the responses of plants to water deficit and other stresses. During water deficit, the cohesion–tension mechanism of the ascent of sap in the xylem plays an important role. Results are summarized which prove the validity of the coehesion/tension theory. Effects of the stress hormone abscisic acid (ABA) are presented. They show that there is an apoplastic component of the flow of ABA in the root which contributes to the ABA signal in the xylem. On the other hand, (+)-cis-trans-ABA specifically affects both the cell level (water channel activity) and water flow driven by gradients in osmotic pressure at the root level which is in agreement with the composite transport model. Hydraulic water flow in the presence of gradients in hydrostatic pressure remains unchanged. The results agree with the composite transport model and resemble earlier findings of high salinity obtained for the cell (Lp) and root (Lpr) level. They are in line with known effects of nutrient deprivation on root Lpr and the diurnal rhythm of root Lpr recently found in roots of Lotus.
Key words: Composite transport, hydraulic conductivity, regulation, root, stress, water deficit, water uptake.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  M. Mahdieh, A. Mostajeran, T. Horie, and M. Katsuhara Drought Stress Alters Water Relations and Expression of PIP-Type Aquaporin Genes in Nicotiana tabacum Plants Plant Cell Physiol., May 1, 2008; 49(5): 801 - 813. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. X. Kim and E. Steudle Light and turgor affect the water permeability (aquaporins) of parenchyma cells in the midrib of leaves of Zea mays J. Exp. Bot., December 7, 2007; (2007) erm270v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. de Lorenzo, F. Merchan, S. Blanchet, M. Megias, F. Frugier, M. Crespi, and C. Sousa Differential Expression of the TFIIIA Regulatory Pathway in Response to Salt Stress between Medicago truncatula Genotypes Plant Physiology, December 1, 2007; 145(4): 1521 - 1532. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Jiang, B. Yang, N. S. Harris, and M. K. Deyholos Comparative proteomic analysis of NaCl stress-responsive proteins in Arabidopsis roots J. Exp. Bot., October 4, 2007; (2007) erm207v1. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Kanai, K. Ohkura, J. J. Adu-Gyamfi, P. K. Mohapatra, N. T. Nguyen, H. Saneoka, and K. Fujita Depression of sink activity precedes the inhibition of biomass production in tomato plants subjected to potassium deficiency stress J. Exp. Bot., August 1, 2007; 58(11): 2917 - 2928. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Teakle, T. Flowers, D Real, and T. Colmer Lotus tenuis tolerates the interactive effects of salinity and waterlogging by 'excluding' Na+ and Cl- from the xylem J. Exp. Bot., June 1, 2007; 58(8): 2169 - 2180. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Pierret, C. Doussan, Y. Capowiez, F. Bastardie, and L. Pages Root Functional Architecture: A Framework for Modeling the Interplay between Roots and Soil Vadose Zone J., May 17, 2007; 6(2): 269 - 281. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Clearwater, P Blattmann, Z Luo, and R. Lowe Control of scion vigour by kiwifruit rootstocks is correlated with spring root pressure phenology J. Exp. Bot., May 1, 2007; 58(7): 1741 - 1751. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. AROCA, A. FERRANTE, P. VERNIERI, and M. J. CHRISPEELS Drought, Abscisic Acid and Transpiration Rate Effects on the Regulation of PIP Aquaporin Gene Expression and Abundance in Phaseolus vulgaris Plants Ann. Bot., December 1, 2006; 98(6): 1301 - 1310. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. H. Maseda and R. J. Fernandez Stay wet or else: three ways in which plants can adjust hydraulically to their environment J. Exp. Bot., December 1, 2006; 57(15): 3963 - 3977. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Ortega, S. C. Fry, and E. Taleisnik Why are Chloris gayana leaves shorter in salt-affected plants? Analyses in the elongation zone J. Exp. Bot., November 1, 2006; 57(14): 3945 - 3952. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. HUANG, Z. YE, R. W. BELL, and B. DELL Boron Nutrition and Chilling Tolerance of Warm Climate Crop Species Ann. Bot., October 1, 2005; 96(5): 755 - 767. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Boursiac, S. Chen, D.-T. Luu, M. Sorieul, N. van den Dries, and C. Maurel Early Effects of Salinity on Water Transport in Arabidopsis Roots. Molecular and Cellular Features of Aquaporin Expression Plant Physiology, October 1, 2005; 139(2): 790 - 805. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Keller Deficit Irrigation and Vine Mineral Nutrition Am. J. Enol. Vitic., September 1, 2005; 56(3): 267 - 283. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Melkonian, L.-X. Yu, and T. L. Setter Chilling responses of maize (Zea mays L.) seedlings: root hydraulic conductance, abscisic acid, and stomatal conductance J. Exp. Bot., August 1, 2004; 55(403): 1751 - 1760. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H.-L. Lian, X. Yu, Q. Ye, X.-S. Ding, Y. Kitagawa, S.-S. Kwak, W.-A. Su, and Z.-C. Tang The Role of Aquaporin RWC3 in Drought Avoidance in Rice Plant Cell Physiol., April 15, 2004; 45(4): 481 - 489. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y.-H. Peng, Y.-F. Zhu, Y.-Q. Mao, S.-M. Wang, W.-A. Su, and Z.-C. Tang Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+ J. Exp. Bot., April 1, 2004; 55(398): 939 - 949. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Wan, E. Steudle, and W. Hartung Gating of water channels (aquaporins) in cortical cells of young corn roots by mechanical stimuli (pressure pulses): effects of ABA and of HgCl2 J. Exp. Bot., February 1, 2004; 55(396): 411 - 422. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Ranathunge, L. Kotula, E. Steudle, and R. Lafitte Water permeability and reflection coefficient of the outer part of young rice roots are differently affected by closure of water channels (aquaporins) or blockage of apoplastic pores J. Exp. Bot., February 1, 2004; 55(396): 433 - 447. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Q. Ye, B. Wiera, and E. Steudle A cohesion/tension mechanism explains the gating of water channels (aquaporins) in Chara internodes by high concentration J. Exp. Bot., February 1, 2004; 55(396): 449 - 461. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Fujita, M. Okada, K. Lei, J. Ito, K. Ohkura, J. J. Adu-Gyamfi, and P. K. Mohapatra Effect of P-deficiency on photoassimilate partitioning and rhythmic changes in fruit and stem diameter of tomato (Lycopersicon esculentum) during fruit growth J. Exp. Bot., November 1, 2003; 54(392): 2519 - 2528. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. H. Lee, A. P. Singh, G. C. Chung, Y. S. Kim, and I. B. Kong Chilling root temperature causes rapid ultrastructural changes in cortical cells of cucumber (Cucumis sativus L.) root tips J. Exp. Bot., November 1, 2002; 53(378): 2225 - 2237. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. JAVOT and C. MAUREL The Role of Aquaporins in Root Water Uptake Ann. Bot., September 1, 2002; 90(3): 301 - 313. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. FRICKE Biophysical Limitation of Cell Elongation in Cereal Leaves Ann. Bot., August 1, 2002; 90(2): 157 - 167. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Fricke and W. S. Peters The Biophysics of Leaf Growth in Salt-Stressed Barley. A Study at the Cell Level Plant Physiology, May 1, 2002; 129(1): 374 - 388. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Hose, D.T. Clarkson, E. Steudle, L. Schreiber, and W. Hartung The exodermis: a variable apoplastic barrier J. Exp. Bot., December 1, 2001; 52(365): 2245 - 2264. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Miyamoto, E. Steudle, T. Hirasawa, and R. Lafitte Hydraulic conductivity of rice roots J. Exp. Bot., September 1, 2001; 52(362): 1835 - 1846. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Watson, J. Pritchard, and M. Malone Direct measurement of sodium and potassium in the transpiration stream of salt-excluding and non-excluding varieties of wheat J. Exp. Bot., September 1, 2001; 52(362): 1873 - 1881. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Génard, S. Fishman, G. Vercambre, J.-G. Huguet, C. Bussi, J. Besset, and R. Habib A Biophysical Analysis of Stem and Root Diameter Variations in Woody Plants Plant Physiology, May 1, 2001; 126(1): 188 - 202. [Abstract] [Full Text]
|
|
|
|
|
|
P. Martre, G. B. North, and P. S. Nobel Hydraulic Conductance and Mercury-Sensitive Water Transport for Roots of Opuntia acanthocarpa in Relation to Soil Drying and Rewetting Plant Physiology, May 1, 2001; 126(1): 352 - 362. [Abstract] [Full Text]
|
|
|
|
|
|
T. C. Hsiao and L.-K. Xu Sensitivity of growth of roots versus leaves to water stress: biophysical analysis and relation to water transport J. Exp. Bot., September 1, 2000; 51(350): 1595 - 1616. [Abstract] [Full Text] [PDF]
|
|