A Novel Approach to the Water Uptake Dynamics in Roots of Maize, Wheat and Barley Under Salt Stress

doi:10.1016/S1671-2927(00)8577

摘要/Abstract

摘要： The water uptake dynamics in maize, wheat, and barley under salt stress were investigated with a xylem pressure probe. The average xylem pressure responses to salt stress in the three plants were 36, 93, and 89% of the osmotic stresses for maize, wheat, and barley, respectively, which are significantly smaller than the magnitude of the osmotic stresses being applied. In order to explain the thermodynamic discrepancies among the water potential changes in the root xylem of the three plants, a novel approach, tentatively named the “symplastic flow dilution model” was proposed in this paper. The model was presented in an attempt to give answers to the problem of how the roots under salt stress could absorb water when the water potential of the xylem sap is considerably higher than that of the solution in the root ambient. According to the model, the salt solution in the microenvironment of the endodermis of a root was diluted to some extent by the efflux from cells so the central stele of the root is not exposed to the same solution bathing the root with the same salt concentration. In contrast, we also presented another approach, the “reflection coefficient progression approach”, which was less likely to be true because it requires a considerable amount of solute to be transported into the root xylem when the salt stress is severe.

关键词: maize, wheat, barley, salt stress, xylem pressure, water transport

Abstract: The water uptake dynamics in maize, wheat, and barley under salt stress were investigated with a xylem pressure probe. The average xylem pressure responses to salt stress in the three plants were 36, 93, and 89% of the osmotic stresses for maize, wheat, and barley, respectively, which are significantly smaller than the magnitude of the osmotic stresses being applied. In order to explain the thermodynamic discrepancies among the water potential changes in the root xylem of the three plants, a novel approach, tentatively named the “symplastic flow dilution model” was proposed in this paper. The model was presented in an attempt to give answers to the problem of how the roots under salt stress could absorb water when the water potential of the xylem sap is considerably higher than that of the solution in the root ambient. According to the model, the salt solution in the microenvironment of the endodermis of a root was diluted to some extent by the efflux from cells so the central stele of the root is not exposed to the same solution bathing the root with the same salt concentration. In contrast, we also presented another approach, the “reflection coefficient progression approach”, which was less likely to be true because it requires a considerable amount of solute to be transported into the root xylem when the salt stress is severe.

Key words: maize, wheat, barley, salt stress, xylem pressure, water transport

BU Qing-mei, BIAN Dian-xia, LIU Lin-de , ZHU Jian-jun. A Novel Approach to the Water Uptake Dynamics in Roots of Maize, Wheat and Barley Under Salt Stress[J]. Journal of Integrative Agriculture, 2012, 12(4): 576-584.

参考文献

[1]Bai X F, Zhu J J, Zhang P, Wang Y H, Yang L Q, Zhang L. 2007. Na+ and water uptake in relation to the radial reflection coefficient of root in arrowleaf saltbush under salt stress. Journal of Integrative Plant Biology, 49, 1334-1340.

[2]Balling A, Zimmermann U. 1990. Comparative measurements of the xylem pressure of Nicotiana plants by means of the pressure bomb and pressure probe. Planta, 182, 325-338.

[3]Canny M J. 1995. A new theory for the ascent of sap: cohesion supported by tissue pressure. Annuals of Botany, 75, 343-357.

[4]Canny M J. 1998. Transporting water in plants. American Scientist, 86, 152-159.

[5]Dainty J, Ginzburg B Z. 1964. The reflection of coefficient of plant cell membranes for certain solutes. Biochimica et Biophysica Acta (Specialized Section on Biophysical Subjects), 79, 129-137.

[6]Enns L C, Canny M J, McCully M E. 2000. An investigation of the role of solutes in the xylem sap and in the xylem parenchyma as the source of root pressure. Protoplasma, 211, 183-197.

[7]Enns L C, McCully M E, Canny M J. 1998. Solute concentrations in xylem sap along vessels of maize primary roots at high root pressure. Journal of Experimental Botany, 29, 1539-1544.

[8]Fiscus E L. 1977. Determination of hydraulic and osmotic properties of soybean root systems. Plant Physiology, 59, 1013-1020.

[9]Ginsburg H, Ginsburg B Z. 1970. Radial water and solute flows in roots of Zea mays. Journal of Experimental Botany, 21, 580-592.

[10]Hanson P J, Sucoff E I, Markhart A H. 1985. Quantifying apoplastic flux through red pine root systems using trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate. Plant Physiology, 77, 21-24.

[11]Hose E, Clarkson D T, Steudle E, Schreiber L, Hartung W. 2001. The exodermis -a variable apoplastic barrier. Journal of Experimental Botany, 52, 2245-2264.

[12]House C R. 1974. Water Transport in Cells and Tissues. Edward Arnold, London. Miller D M. 1985a. Studies of root function in Zea mays. III. Xylem sap composition at maximum root pressure provides evidence of active transport into the xylem and a measurement of the reflection coefficient of the root. Plant Physiology, 77, 162-167.

[13]Miller D M. 1985b. Studies of root function in Zea mays. IV. Effects of applied pressure on the hydraulic conductivity and volume flow through the excised root. Plant Physiology, 77, 168-174.

[14]Miyamoto N, Steudle E, Hirasawa T, Lafitte R. 2001. Hydraulic conductivity of rice roots. Journal of Experimental Botany, 52, 1835-1846.

[15]Munns R, Passioura J B. 1984. Effect of prolonged exposure to NaCl on the osmotic pressure of leaf xylem sap from intact, transpiting barley plants. Australian Journal of Plant Physiology, 11, 497-507.

[16]Ranathunge K, Kotula L, Steudle E, Lafitte R. 2004. 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. Journal of Experimental Botany, 55, 433-447.

[17]Rygol J, Zimmermann U. 1990. Radial and axial turgor pressure measurements in individual root cells of Mesembryanthemum crystallinum grown under various saline conditions. Plant, Cell and Environment, 13, 15-26.

[18]Rygol J, Pritchard J, Zhu J J, Tomos A D, Zimmermann U. 1993. Transpiration induces radial turgor pressure gradients in wheat and maize roots. Plant Physiology, 103, 493-500.

[19]Schneider H, Zhu J J, Zimmermann U. 1997. Xylem and cell turgor pressure probe measurements in intact roots of glycophytes: transpiration induces a change in the radial and cellular reflection coefficients. Plant Cell Environment, 20, 221-229.

[20]Shabala S, Shabala S, Cuin T A, Pang J, Percey W, Chen Z, Conn S, Eing C, Wegner L H. 2010. Xylem ionic relations and salinity tolerance in barley. The Plant Journal, 61, 839-853.

[21]Steudle E. 2002. Transport of water in plants. Environment Control in Biology, 40, 29-37.

[22]Steudle E, Murrmann M, Peterson C A. 1993. Transport of water and solutes across maize roots modified by puncturing the endodermis: further evidence of the composite transport model of the root. Plant Physiology, 103, 335-349.

[23]Steudle E, Peterson C A. 1998. How does water get through roots? Journal of Experimental Botany, 49, 775-788.

[24]Varney G T, McCully M E, Canny M J. 1993. Sites of entry of water into the symplast of maize roots. New Phytologist, 125, 733-741.

[25]Weatherley P E. 1982. Water uptake and flow in roots. In: Lange O L, Nobel P S, Osmond C B, Ziegler H, eds., Encyclopedia of Plant Physiology, New Series, vol. 12B. Water Relations and Carbon Assimilation, Springer-Verlag, Berlin. pp. 79-109.

[26]Wei C, Tyree M T, Steudle E. 1999. Direct measurement of xylem pressure in leaves of intact maize plants. A test of the cohesion-tension theory taking hydraulic architecture into consideration. Plant Physiology, 121, 1191-1205.

[27]Zholkevich V N, Chugunova T V, Kordev A V. 1990. New data on the nature of root pressure. Studia Biophysica, 130, 209-216.

[28]Zhu J J, Bai X F, Zhang P, Bu Q M. 2005. Self-regulation of xylem pressure in barley roots under salt stress. Journal of Plant Physiology and Molecular Biology, 31, 97-102. (in Chinese)

[29]Zhu J J, Zimmermann U, Thürmer F, Haase A. 1995. Xylem pressure in maize roots subjected to osmotic stress: determination of radial reflection coefficients by using the xylem pressure probe. Plant Cell and Environment, 18, 906-912.

[30]Zimmermann U, Haase A, Langbein D, Meinzer F. 1993. Mechanism of long-distance water transport in plants: a re-examination of some paradigms in the light of new evidence. Philosophical Transactions of the Royal Society London, 341, 19-31.

[31]Zimmermann U, Rygol J, Balling A, Klock G, Metzler A, Haase A. 1992. Radial turgor and osmotic pressure profiles in intact and excised roots of Aster tripolium. Pressure probe measurements and nuclear magnetic resonance-imaging analysis. Plant Physiology, 99, 186-196.

[32]Zimmermann U, Zhu J J, Meinzer F C, Goldstein G, Schneider H, Zimmermann G, Benkert R, Thurmer F, Melcher P, Webb D, et al. 1994. High molecular weight organic compounds in the xylem sap of mangroves: implications for long-distance water transport. Botanica Acta, 107, 218-229.