Water transport across biological membranes

Haines, Thomas H.

doi:10.1016/0014-5793(94)00470-6

Cited by 102 publications

(71 citation statements)

References 48 publications

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“…Additionally, stomata would be expected to take several minutes to close, while the increase in R leaf with chilling occurred smoothly over time and ceased when temperature was held constant at any chilling temperature. The greater-than viscosity temperature response of R leaf is consistent with the flow path including a transcellular component (Haines, 1994). This temperature response is the first to be reported for steady-state water flow through individual leaves; previously, milder effects (but still greater than those expected for viscosity) have been reported for leafy shoots (Fredeen and Sage, 1999;Cochard et al, 2000;Matzner and Comstock, 2001).…”

Section: Partitioning Of Leaf Hydraulic Resistance: Water Flow Througsupporting

confidence: 82%

“…We combined these measurements with an analog circuit model to determine whether these component resistances, set in reticulate hierarchical venation with water leaking to the mesophyll and eventually to the sites of evaporation, can be considered as resistors additive in series. Temperature responses were used to diagnose whether water moving through the leaf crosses cell membranes into the symplast, as opposed to taking place entirely in the apoplast (Haines, 1994;Martre et al, 2002).…”

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confidence: 99%

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Hydraulic Analysis of Water Flow through Leaves of Sugar Maple and Red Oak

2004

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Leaves constitute a substantial fraction of the total resistance to water flow through plants. A key question is how hydraulic resistance within the leaf is distributed among petiole, major veins, minor veins, and the pathways downstream of the veins. We partitioned the leaf hydraulic resistance (R leaf ) for sugar maple (Acer saccharum) and red oak (Quercus rubra) by measuring the resistance to water flow through leaves before and after cutting specific vein orders. Simulations using an electronic circuit analog with resistors arranged in a hierarchical reticulate network justified the partitioning of total R leaf into component additive resistances. On average 64% and 74% of the R leaf was situated within the leaf xylem for sugar maple and red oak, respectively. Substantial resistance-32% and 49%-was in the minor venation, 18% and 21% in the major venation, and 14% and 4% in the petiole. The large number of parallel paths (i.e. a large transfer surface) for water leaving the minor veins through the bundle sheath and out of the leaf resulted in the pathways outside the venation comprising only 36% and 26% of R leaf . Changing leaf temperature during measurement of R leaf for intact leaves resulted in a temperature response beyond that expected from changes in viscosity. The extra response was not found for leaves with veins cut, indicating that water crosses cell membranes after it leaves the xylem. The large proportion of resistance in the venation can explain why stomata respond to leaf xylem damage and cavitation. The hydraulic importance of the leaf vein system suggests that the diversity of vein system architectures observed in angiosperms may reflect variation in whole-leaf hydraulic capacity.Water flow through the leaf is one of the most important but least understood components of the whole-plant hydraulic system. The leaf hydraulic resistance (R leaf ) constitutes a significant hydraulic bottleneck, correlates with leaf structure, and apparently constrains gas exchange (Tyree and Zimmermann, 2002;Sack et al., 2003b;Sack and Tyree, 2004). R leaf is an aggregate measure; once past the petiole, water flows through a reticulate network of veins, across the bundle sheath cells, and through or around mesophyll cells before evaporation and diffusion from the stomata (Esau, 1965). Recent work has focused primarily on measurement of R leaf and its functional correlates. Few studies have attempted to determine quantitatively how the various components of the water flow pathway through the leaf contribute to its total resistance.Partitioning of R leaf is a crucial step for understanding leaf hydraulic design. Cavitation in the leaf vein xylem can substantially increase R leaf , as can physical damage to major veins; both drive reductions of leaf water potential and gas exchange Nardini et al., 2001Cochard et al., 2002;Huve et al., 2002;Sack et al., 2003a). These observations suggest that a large proportion of R leaf is situated in the veins. However, a number of studies have reported that most of the leaf resista...

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Section: Partitioning Of Leaf Hydraulic Resistance: Water Flow Througsupporting

confidence: 82%

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confidence: 99%

Hydraulic Analysis of Water Flow through Leaves of Sugar Maple and Red Oak

2004

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“…Despite the fact that biological membranes are generally impermeable to ionic compounds, the small size of water molecules allows them to diffuse passively across cellular membranes, moving through the defects or vacancies of the bilayer as the lipids diffuse laterally through the membrane (18)(19)(20).…”

Section: Discussionmentioning

confidence: 99%

“…We calibrate laboratory standards to the international standards and then include the laboratory standards as internal standards in every run. Stable isotope contents are expressed in ''delta'' notation as ␦ values in parts per thousand (‰), where ␦‰ ϭ (R A ͞R Std Ϫ 1)⅐1,000‰, and R A and R Std are the molar ratios of the rare to abundant isotope (e.g., 18 O͞ 16 O) in the sample and the standard. The standard used for both oxygen and hydrogen is Vienna standard mean ocean water (11).…”

Section: Methodsmentioning

confidence: 99%

Oxygen isotopes indicate most intracellular water in log-phase Escherichia coli is derived from metabolism

Kreuzer-Martin

Ehleringer

Hegg

2005

Proc. Natl. Acad. Sci. U.S.A.

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The transport of water into and out of unicellular organisms is a seemingly simple process in which water diffuses either through pores or directly across the membrane. Because of the rates at which water can theoretically diffuse, it is generally accepted that intracellular water is indistinguishable from extracellular water. Using stable isotope ratio mass spectrometry, we directly tested this assumption. Here we demonstrate that under active growth, up to 70% of the intracellular water in log-phase Escherichia coli cells was actually generated during metabolism and was isotopically distinct from extracellular water. The contribution of metabolism to intracellular water was substantially less in stationaryphase or quiescent cells.stable isotope ͉ mass spectrometry ͉ water transport S table isotopes are commonly used as a tool for probing complex biological and environmental processes. For instance, at the cellular level, hydrogen, carbon, nitrogen, and oxygen isotopes are often used to dissect reaction mechanisms and as tracers to follow metabolic pathways. On a more global level, these same isotopes are used in ecological studies to probe the relationship among environmental nutrients, water, and organic molecules and biological tissues. Information from these studies can be used to deduce information about the growth environment of an organism or source of a sample from its isotope ratios (1-3). A common approach to environmental reconstruction by geochemists is the analysis of isotope ratios of biomarkers, resistant biogenic molecules, to infer the conditions under which the metabolites were formed (4). Because the hydrogen and oxygen isotope ratios of precipitation are strongly influenced by environmental variables, these elements are of particular utility in both paleoclimate and forensic studies.Studies of isotopic relationships between growth water and organic components of organisms are often carried out under laboratory conditions to determine fractionation factors between organism and environment. The results from these studies are then used to infer information about the growth environment that led to the production of the same compounds isolated from environmental samples. Two implicit assumptions are nearly always made during environmental reconstruction. The first is that intracellular water is isotopically identical to extracellular water (5, 6). This idea is based on the notion that water inside of a cell should be in rapid equilibrium with water outside of the cell. The second assumption is that the isotopic fractionations determined from cellular studies performed in the laboratory will be equivalent to those ratios measured in the natural environment.We recently questioned the validity of these two common assumptions when studying the biosynthesis of heme O. When Escherichia coli cells were grown in the laboratory in 2ϫ LB prepared with 95% H 2 18 O, Ϸ40% of the heme O molecules contained a labeled oxygen atom in the 17-hydroxyethylfarnesyl moiety (7), despite the fact that this oxygen atom ...

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“…Before dismissing an aquaporin as physiologically nonessential, careful testing of possible conditional phenotypes is , and surface area of Ϸ5 m 2 , the doubling of bacterial volume could easily be provided by the diffusional water permeability of simple lipid bilayers, P d from 2-50 m͞sec, (33), especially because the surface-to-volume ratio is much higher for bacteria than mammalian cells. Diffusional water permeability is known to have a high Arrhenius activation energy (Ϸ10 kcal͞mol), so water permeability should be maximum at the highest temperatures, suggesting that aquaporins would be less important.…”

Section: Discussionmentioning

confidence: 99%

Regulation of the Escherichia coli water channel gene aqpZ

Calamita

Kempf

Bonhivers

et al. 1998

Proc. Natl. Acad. Sci. U.S.A.

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Osmotic movement of water across bacterial cell membranes is postulated to be a homeostatic mechanism for maintaining cell turgor. The molecular water transporter remained elusive until discovery of the Escherichia coli water channel, AqpZ, however the regulation of the aqpZ gene expression and physiological function of the AqpZ protein are unknown. Northern analysis revealed a transcript of 0.7 kb, confirming the monocistronic nature of aqpZ. Regulatory studies performed with an aqpZ::lacZ low copy plasmid demonstrate enhanced expression during mid-logarithmic growth, and expression of the gene is dependent upon the extracellular osmolality, which increased in hypoosmotic environments but strongly reduced in hyperosmolar NaCl or KCl. While disruption of the chromosomal aqpZ is not lethal for E. coli, the colonies of the aqpZ knockout mutant are smaller than those of the parental wild-type strain. When cocultured with parental wild-type E. coli, the aqpZ knockout mutant exhibits markedly reduced colony formation when grown at 39°C. Similarly, the aqpZ knockout mutant also exhibits greatly reduced colony formation when grown at low osmolality, but this phenotype is reversed by overexpression of AqpZ protein. These results implicate AqpZ as a participant in the adaptive response of E. coli to hypoosmotic environments and indicate a requirement for AqpZ by rapidly growing cells.

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Water transport across biological membranes

Cited by 102 publications

References 48 publications

Hydraulic Analysis of Water Flow through Leaves of Sugar Maple and Red Oak

Hydraulic Analysis of Water Flow through Leaves of Sugar Maple and Red Oak

Oxygen isotopes indicate most intracellular water in log-phase Escherichia coli is derived from metabolism

Regulation of the Escherichia coli water channel gene aqpZ

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