Journal of Experimental Botany, Vol. 51, No. 345, pp. 769-776,
April 2000
© 2000 Oxford University Press
Fluid ionic composition influences hydraulic conductance of xylem conduits
Department of Plant Sciences, Horticultural Production Chains group, Wageningen University, Marijkeweg 22, 6709 PG, Wageningen, The Netherlands
Received 23 July 1999; Accepted 22 December 1999
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Abstract |
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The direct effect of fluid composition on xylem hydraulic conductance is investigated in excised stem segments of chrysanthemum (Dendranthemax grandiflorum Tzvelev cv. Cassa) plants. Dynamic changes in hydraulic conductance are accurately measured at 30 s intervals before and after modifications of the composition of the standard fluid (deionized water). It is investigated whether osmotic properties of the flowing solution influence overall hydraulic conductance by affecting the hydraulic conductance of vessel-to-vessel pit membranes, as has previously been suggested. Various iso-osmotic salt solutions (20 mOsm kg-1) of different composition raised the hydraulic conductance of 20 cm long stem segments approximately 5–8% compared to deionized water. In contrast, carbohydrate solutions with similar osmotic strength and pH did not cause any change in hydraulic conductance. KCl solutions that greatly differed in osmotic strength all increased hydraulic conductance, but the response was not correlated with the osmotic strength of the solution. Increasing the number of vessels that were open from one cut end to the other by shortening the stem segments greatly increased the hydraulic conductance response. Changing from deionized water to a salt solution caused an immediate increase in hydraulic conductance, while a shift back to deionized water resulted in a slow decline. This decline lasted longer when the salt solution contained divalent cations compared to monovalent cations. It is concluded that the presence of cations and not the osmotic strength in the flowing solution influenced the hydraulic conductance. The phenomenon is not caused by the vessel-to-vessel pit membranes, which in fact suppressed the effect, due to their large contribution to the overall resistance to water flow.
Key words: Xylem vessel, resistance, water flow, salts.
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Introduction |
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In vascular plants, xylem conduits form the major path for water transport from roots to leaves. Therefore, their functioning has been of interest for more than a century (Dixon and Joly, 1894
). Currently, it is generally thought that fluid flow through xylem conduits is pressure driven and respects Hagen–Poiseuille's law. Analogous with this law, the hydraulic conductance of the xylem is assumed to be mainly dependent on the geometry of the xylem conduits (Dimond, 1966; Pickard, 1981; Zimmermann, 1983). Attempts to verify this analogue with Hagen–Poiseuille by measuring the hydraulic conductance of a stem segment and comparing this with an estimated hydraulic conductance based on diameters of xylem vessels have shown variable results (Dimond, 1966; Zimmermann, 1983). Serious deviations were observed even when the measurements were done on single vessels (Giordano et al., 1978). Through the years, various explanations for these discrepancies have been proposed which roughly can be separated into two groups. The first group tries to explain deviations within the Hagen–Poiseuille analogue and concentrates on short-term variation in vessel diameters, the role of scalariform perforation plates (Schulte and Castle, 1993; Ellerby and Ennos, 1998) and vessel ends (Chiu and Ewers, 1993; Zimmermann, 1978), or the existence of air-embolisms or other physical blockages in xylem vessels (Sperry et al., 1988). The second group focuses on the shortcomings of the Hagen–Poiseulle analogue due to the implicit assumptions (Giordano et al., 1978) or even questions the underlying cohesion–tension theory of sap flow in plants (reviewed by Tyree, 1997; Canny, 1995; Milburn, 1996; Zimmermann et al., 1993).
Besides the anatomy of the conducting xylem, properties of the conducted fluid may also influence xylem hydraulic conductance. According to Hagen–Poiseuille, hydraulic conductance also depends on viscosity of the fluid, which is affected by temperature and concentration of solutes (Pickard, 1981). The concentration of solutes in xylem sap is normally low (Liang and Zhang, 1997) and therefore hardly influences viscosity of the xylem sap (Pickard, 1981). The temperature response on fluid flow rate is limited to approximately 2.3% °C-1, between 10 °C and 30 °C (Nobel, 1983) and is usually taken into account when xylem hydraulic conductance is determined (Sperry et al., 1988).
It is known that properties of the fluid may also influence the long-term decrease of xylem hydraulic conductance over time, which often occurs during hydraulic conductance determinations on excised stem segments. It has been claimed that dilute KCl solutions (0.01–0.1 M) prevented this long-term decline in stem segments of sugar maple (Acer saccharum Marsh.) (Zimmermann, 1978). However, other experiments on sugar maple did not confirm these observations (Sperry et al., 1988). It was observed that dilute fixatives (e.g. 0.05% formaldehyde) and acid solutions (pH<3) prevented or delayed this long-term decline. This was explained by the inhibitory effect of these fluid properties on microbial growth, which otherwise increasingly obstructs fluid flow during long-term hydraulic conductance measurements on excised plant material (Sperry et al., 1988). It has also been reported that the decrease in hydraulic conductance of stem segments of chrysanthemum cut flowers (Dendranthemaxgrandiflorum Tzvelev) during vase life was much higher when deionized water was used instead of tap water (Van Meeteren et al., 1999).
This paper focuses on another phenomenon related to the effect of fluid properties on xylem hydraulic resistance. Fluid properties do not only influence xylem hydraulic conductance in the long term. A large increase in hydraulic conductance (
20%) in sugar maple stem segments has been observed (Zimmermann, 1978), immediately after the fluid was changed from distilled water to tap water. Zimmermann attributed this phenomenon to swelling and shrinking of the vessel-to-vessel pit membranes due to variation in osmotic strength of the flowing solution. However, he did not include the experimental evidence for this explanation. Nevertheless, based on these findings the use of solutions with some osmotic strength (20–100 mOsm kg-1) became common in hydraulic conductance determinations. Further investigation of this phenomenon may add valuable information to the discussion about the Hagen–Poiseuille analogue for xylem hydraulic conductance.
The aim of the present research was to investigate whether measurements of the xylem hydraulic conductance of the herbaceous perennial Dendranthemax grandiflorum Tzvelev (chrysanthemum) are also directly influenced by fluid composition as previously observed in branches of the sugar maple tree. Furthermore, it was investigated whether observed short-term effects of fluid composition on xylem hydraulic conductance could be attributed to the osmotic properties of the fluid by affecting the hydraulic conductance of vessel-to-vessel pit membranes. Therefore, dynamic changes in xylem hydraulic conductance were accurately measured on stem segments of chrysanthemum plants, while varying fluid composition. The role of vessel-to-vessel pit membranes was investigated using stem segments of different length, thus varying the number of continuous open vessels in the stem segments (Chiu and Ewers, 1993).
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Plant material and preparation of samples
Chrysanthemum (Dendranthemaxgrandiflorum Tzvelev cv. Cassa) plants were grown in a greenhouse in pots until commercial maturity (Van Meeteren and Van Gelder, 1999
). Stem segments of fully turgid plants were cut under deionized water and re-cut with a new razor blade to a length of approximately 20 cm. Unless otherwise mentioned, the basal cut end was located at 15 cm height, measured from the base of the plant. According to the vessel length distribution, previously determined on stem segments of similary grown chrysanthemum plants of the same cultivar using the latex particle method (Zimmermann and Jeje, 1981), the 20 cm length ensured that few if any vessels were open from the base cut end to the top. A piece of silicon tubing was wrapped over the upper cut end of the stem segment (the cut end closest to the apex in the intact plant) to enable connection to the apparatus for hydraulic conductivity measurements (described below). The stem segment sample was continuously kept under deionized water until attachment to the apparatus. The time between cutting and start of a conductivity measurement did not exceed 20 min.
Apparatus to measure hydraulic conductance
A schematic representation of the apparatus to measure hydraulic conductance is given in Fig. 1. A digital peristaltic pump (505DI Watsom-Marlow Limited, Falmouth, England) in combination with a vacuum sensor (VAP 5/DVR5; Vacuubrand, Gmbh & Co, Wertheim, Germany) and personal computer were used to control the below-atmospheric pressure at the top of the stem segment. In most experiments an absolute pressure difference of 40.0±0.01 kPa was induced along the stem segments. This pulling pressure was the driving force for flow of fluid from the lower to the upper cut end of the stem segments (natural direction). Fluid flow rate was measured by recording weight loss of containers filled with solution on high precision balances (LP3200D, Sartorius AG, Goettingen, Germany) at intervals of 30 s. Specially developed software running on a personal computer which was connected to the balances provided on-line graphs of measured fluid flow rate. Corrections were made for direct evaporation from the containers on the balances, which was measured immediately before and after each experiment. Measurements were done at constant temperature of ambient air and fluid (20±0.5 °C).
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General measurement procedure
A typical measurement procedure consisted of two or three phases. It started with an initial period of 15–45 min of measuring fluid flow rate of deionized water at a pressure difference of 40.0 kPa between the two ends of the stem segment until the measured flow rate was constant for at least 10 min. Then the container with deionized water was exchanged for a container of the solution of interest. To prevent air entering open vessels at the lower cut end of the stem segments during this exchange of solutions, the pulling pressure on the top of the stem segment was reversed to a small gravity induced above-atmospheric pressure (1–2 kPa). After the exchange of solutions the pulling pressure was restored and a 10–30 min period of fluid flow rate measurements followed. In some, but not all, experiments this second phase was followed by a third, starting with a shift back to deionized water (while preventing air entry), and followed by a 30–90 min period of continuous fluid flow rate measurements.
Tests were done to find out whether absolute fluid flow rate influenced the percentage increase in hydraulic conductance after changes from deionized water to 0.1 M KCl solution. Therefore, hydraulic conductance was measured before and after the change in solution at several pressure differences (5, 10, 20, 30, 40, and 50 kPa) over two 20 cm long stem segments.
Changes in fluid osmotic strength and xylem hydraulic conductance
To investigate the role of the osmotic strength of the fluid and the effect of some specific solutes on xylem hydraulic conductance, short-term changes (<1 h) in fluid flow rate were measured while the pressure difference over the stem segment (40.0 kPa) was kept constant. Effects of iso-osmotic (20 mOsm kg-1) saline and non-saline solutions were investigated. Solutions containing various combinations of monovalent and divalent cations and anions (KCl, K2SO4, NaCl, CaCl2, MgSO4) in appropriate concentrations were tested and compared with mannitol and melizitose solutions of the same osmotic strength. Secondly, the effect of a range of KCl solutions of different concentration (1x10-5–2x10-1 M) and hence different osmotic strength (0–400 mOsm kg-1) were tested. Before use, osmolality of all applied solutions was measured by cryoscopy (micro-osmometer Model 3B, Roebling, Berlin)
Role of vessel-to-vessel pit membranes
To investigate whether changes in hydraulic conductance of vessel-to-vessel pit membranes are involved in the short-term response to changes in solution, measurements were done on long (20 cm), short (3 cm) and very short (1.5 cm) stem segments. According to the vessel length distribution, previously measured with the latex particle method (Zimmermann and Jeje, 1981) on similarly grown chrysanthemum plants of the same cultivar, almost no vessels (<1%) are open from bottom to top in 20 cm long stem segments. Approximately 50% and 75% of the vessels are open in 3 and 1.5 cm long stem segments, respectively.
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Results |
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General
The hydraulic conductance pattern of 20 cm long stem segments during a typical experiment in which the solution was changed is shown in Fig. 2
. Hydraulic conductance at the start of a measurement cycle (at deionized water) is set to 100% to normalize the results, which differ slightly between individual samples due to small length differences and natural variation between samples. After a change in flowing solution from deionized water to a solution containing salts, hydraulic conductance generally increased to a higher steady level. This response was immediate as far as could be measured (approximately 2–5 min of flow rate measurements were missed while exchanging solutions). After changing back to deionized water a decrease in hydraulic conductance was observed, which could endure from 20 min up to more than an hour. The final constant hydraulic conductance using deionized water was generally lower than the initially measured hydraulic conductance using deionized water.
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At the start of a measurement cycle sometimes a small transient increase in fluid flow rate was measured. If present, this period of increase usually did not exceed 30 min and appeared in all samples of the same lot of plants. No transient responses were observed after suddenly releasing and re-applying the pulling pressure during a hydraulic conductance determination. Only a few samples showed a prolonged increase in fluid flow rate after 30 min, possibly due to initial presence and recovery from air-embolism in the xylem (Sperry et al., 1988
). Results from these samples are excluded.
Short-term effects of fluid osmotic strength on hydraulic conductance
All tested iso-osmotic salt solutions (20 mOsm kg-1, pH 6.0) increased hydraulic conductance in 20 cm long stem segments approximately 7–8% compared to deionized water (Table 1). No difference in percentage increase in hydraulic conductance was measured between salt solutions composed of different combinations of monovalent or divalent cations and anions. In contrast, solutions containing the carbohydrates mannitol or melizitose did not cause any change in hydraulic conductance, although their osmotic strength and pH were similar to those of the applied salt solutions (20 mOsm kg-1, pH 6.0; (Table 1).
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KH) after changing from deionized water to differently composed solutions of approximately similar osmotic strengthKCl solutions ranging in concentration between 1x10-5 and 2x10-1 M caused increases in hydraulic conductance (relative to deionized water) between 2.5% and 15% (Fig. 3
). No clear relationship was found between the increments in hydraulic conductance and the concentration of the applied KCl solutions. Even at negligible osmotic strength (not measurable using cryoscopy) hydraulic conductance was substantially increased.
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Indicative tests on two stem segments revealed that the percentage increase in hydraulic conductance after changes from deionized water to 0.1 M KCl solution was not influenced by the absolute fluid flow rate.
Effect of stem segment length
Hydraulic conductivity (hydraulic conductance normalized for length) was clearly larger in 3 cm (short) stem segments than in 20 cm (long) stem segments (Table 2). Hydraulic conductivity determined in 1.5 cm stem segments should be interpreted with care because continuously increasing fluid flow rates were observed in all these stem segments, which made reliable hydraulic conductance and conductivity determinations hazardous. In order to determine an indication of the solution effect on hydraulic conductivity in these very short stem segments, flow measurements just before and just after the change in solution were used for hydraulic conductivity determinations. The change in hydraulic conductivity clearly decreased with stem segment length (72%, 12% and 5% in 1.5, 3 and 20 cm long stem segments, respectively; (Table 2).
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Dynamics of hydraulic conductance responses
Hydraulic conductance responses after changes from deionized water to solutions containing dissolved salts were always immediate (Figs 2
, 4). Transient responses after changes back to deionized water differed between salt solutions (Figs 2, 4). Solutions containing monovalent cations (K+, Na+) generally decayed to a new stable hydraulic conductance within 30 min after the change back to deionized water. Solution containing divalent cations (Mg2+ and Ca2+) decayed much more slowly and generally did not reach a new stable hydraulic conductance within the measurement period of 1–1.5 h (Fig. 4). This new stable hydraulic conductance was also not very different from the initial measured hydraulic conductance. Dynamics responses seem not to be related to the anions (Cl- and 
) in the salt solutions. Repeated shifts between deionized water and 0.1 M KCl solution in 20 cm long stem segments resulted in alternating hydraulic conductances between ±93% and 110% of the initial flow rate (see for an example Fig. 2).
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: 0.01 M NaCl; 
: 0.0067 M CaCl2; O: 0.01 M MgSO4) and vice versa. Measurements were done on 20 cm long stem segments at a constant pressure difference of 40.0 kPa over the stem segments. |
Discussion |
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The immediate increase in hydraulic conductance due to changes in fluid composition, as previously reported in stem segments of the tree sugar maple (Zimmermann, 1978
), was also consistently observed in stem segments of the herbaceous perennial chrysanthemum in the present experiments.
Three different types of experiments were carried out to investigate the previously suggested explanation for this short-term increase in hydraulic conductance (Zimmermann, 1978). Zimmermann suggested that the phenomenon was due to a variable hydraulic resistance of vessel-to-vessel pit membranes resulting from changes in osmotic properties of the flowing solution. None of present experiments supported this explanation. In the first experiment, in which the change in hydraulic conductance was induced by differently composed solutions of similar osmotic strength, only solutions containing dissolved salts increased hydraulic conductance. No changes in hydraulic conductance were observed after changing from deionized water to solutions containing mannitol or melizitose (Table 1). This shows that the osmotic strength of the flowing solution was not the primary factor that caused the change in hydraulic conductance. This conclusion is supported by a second experiment, in which a wide range of KCl concentrations was used to induced changes in hydraulic conductance. KCl solutions with a very low osmotic strength (0.001 M KCl 2 mOsm kg-1) and KCl solutions with substantial osmotic strength (0.2 M KCl 400 mOsm kg-1) caused approximately similar changes in hydraulic conductance (Fig. 3). Even very dilute KCl solutions (1x10-5 M), with negligible osmotic strength, caused an increase in hydraulic conductance. These results show that the presence of a small amount of dissolved salts, rather than the overall osmotic strength of the solution caused an increase in xylem hydraulic conductance compared to deionized water. In the third experiment, shortening the stem segment from 20 cm to 3 cm reduced the number of vessel-to-vessel pit membranes in the flow path. This should have decreased the magnitude of the change in hydraulic conductance, providing the pit membrane hypothesis is true. However, instead of a decreasing change in hydraulic conductance with stem segment length, a progressively increasing change in hydraulic conductance was observed after changes from deionized water to salt solutions. With approximately 50% cut open vessels, hydraulic conductance in stem segments of 3 cm length increased by 12% when salt solutions were used compared to 5% in stem segments of 20 cm length with almost no continuous open vessels. The effect was even larger in stem segments of 1.5 cm length with 75% open vessels. However, the latter results must be interpreted with care because the measured flow rate through these very short stem segments did not stabilize within 30 min (Table 2). It is concluded that changes in hydraulic conductance after changing the solution from deionized water to a salt solution were not due to swelling and shrinking of vessel-to-vessel-pit membranes caused by the change in osmotic properties of the fluids. This raises the question, what else might have caused the clearly observed short-term changes in hydraulic conductance?
Changing osmotic gradients between the upper and lower end of the stem segments are not a likely explanation for the observed effects on hydraulic conductance: no effects were measured with osmotically active mannitol and melizitose solutions, while a clear effect was measured with a very low concentration of KCl solution. Moreover, the initial increase in hydraulic conductance after changing from deionized water to salt solution is not facilitated but hampered by an osmotic potential difference between the solutions at the lower and upper cut ends of the stem segments.
Shortening the stem segments from 20 cm to 3 cm greatly increased the hydraulic conductivity of stem segments (Table 2). This indicates that in chrysanthemum stems, pit membrane resistances greatly contribute to the total resistance to water flow, which is in agreement with observations in many other plants (Schulte and Gibson, 1988; Gibson et al., 1985), although not in all (Chiu and Ewers, 1993). Actual prediction of the percentage of overall hydraulic resistance caused by the pit membranes based on the present results is difficult. This is due to a number of reasons, including the non-normal distribution of vessel lengths and diameters, the imperfect correlation between lengths and diameters of vessels and the inhomogeneous conductance distribution along the length of the stem segments (Chiu and Ewers, 1993). The difficulties with determining hydraulic conductance in very short stem segments, which arose when measuring 1.5 cm long stem segments, have been reported in Lonicera fragrantissima (Chiu and Ewers, 1993). These authors also observed a decrease in hydraulic conductivity in stem segments shorter than 2 cm and suggested that this might have been due to an end effect in segments with a high percentage of cut open vessels caused by local turbulence. The increasing effect of solution composition on hydraulic conductivity with decreasing segment length might have been due to a large contribution of the hydraulic resistances of the pit membranes to the total resistance to water flow. If the resistance of the pit membranes is not affected by solution composition and it contributes greatly to the overall resistance of the xylem, which seems to be the case in the present results, then it reduces the change in overall xylem hydraulic conductance due to solution composition. This explains why the observed effect was much larger (up to 70%) in stem segments with fewer pit membranes in the flow path. The main constituents of overall resistance to water flow are the resistance of pit membranes and the lumen resistance (Chiu and Ewers, 1993; Schulte et al., 1993). It seems therefore reasonable to conclude that the observed increasing effect of dissolved salts on hydraulic conductance is caused by considerable modification of the resistance of the lumen walls.
The different dynamic responses of hydraulic conductance after subsequent changes between deionized water and salt solutions and vice versa are obvious (Figs 2, 4). The maximal response in hydraulic conductance is maximal immediately after changing from deionized water to salt solution, which was already induced by a very small amount of dissolved salts (e.g. 1x10-5 M KCl). The response after the reversed change from salt solution to deionized water clearly reflects a decaying process. The duration of this decay was influenced by the valence of the cations in the salt solution, which was used before the shift back to deionized water (Fig. 4). The valence of the tested anions in the salt solutions did not influence the duration of the decay. All dynamic observations point to an explanation related to the cation exchange properties of the xylem cell walls along the transport path. Xylem cell walls contain fixed negative charges, resulting from dissociated polygalacturonic acids yielding COO- groups (Baker and Hall, 1975). Due to these fixed negative charges, cations are accumulated in the cell walls and anions are excluded (Grignon and Sentenac, 1991). Most of the cations are reversibly retained in the cell walls and are easily exchangeable. Differences in associations exist between different cations and the fixed negative charges. In general, divalent cations, such as Mg2+ and Ca2+, are more tightly associated to the negative charges in the cell walls than monovalent cations, such as K+ and Na+ (Grignon and Sentenac, 1991). Based on general principles it may be expected that, after supplying a surplus of cations to the negatively charged groups in the xylem cell walls, saturation of all fixed negatively charged groups with cations takes place almost immediately. Flushing the cations from the cell walls with deionized water takes more time and follows a decaying pattern, of which the duration depends on the binding properties between the cell walls and cations. The different levels of hydraulic conductance measured using deionized water at the start of a measurement cycle or after a period on KCl or NaCl-solution (Figs 2, 4) could have been caused by the initial presence of multivalent cations normally present in xylem sap. Deionized water is probably not able to remove all the associated divalent cations from the negatively charged groups, as is also shown in Fig. 4. A large surplus of monovalent cations in the flowing solution could possibly exchange with the remaining divalent cations in the cell walls, but may later themselves be removed by deionized water, which finally results in a larger number of unmasked negative groups.
It is remarkable that the kinetics of the fluid flow rate after changes from deionized water to salt solutions and vice versa, also follows this pattern of immediate and decaying responses. This raises the question whether the observed phenomenon of changing xylem hydraulic conductance, due to changes in solution composition, could have been due to interactions between fluid flow and the presence or absence of unmasked negatively charged groups along the cell walls of xylem vessels. If true, this would add another shortcoming to the Hagen–Poiseuille analogue for resistance in xylem vessels.
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Acknowledgments |
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This research is supported by the Technology Foundation STW, Applied Science Division of NWO.
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Notes |
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1 To whom correspondence should be addressed. Fax: +31 317 484709. E-mail: Wim.vanIeperen{at}users.tbpt.wag-ur.nl
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References |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Baker DA, Hall JL.1975. Ion transport—introduction and general principles. In: Baker DA, Hall JL, eds. Ion transport in plant cells and tissues. Amsterdam: North Holland Publishing Company, 8–37.
Canny MJ.1995. Apoplastic water and solute movement: new rules for an old space. Annual Review of Plant Physiology and Plant Molecular Biology 46, 215–236.[ISI]
Chiu ST, Ewers FW.1993. The effect of segment length on conductance measurements in Lonicera fragrantissima. Journal of Experimental Botany 44, 175–181.
Dimond AE.1966. Pressure and flow relations in vascular bundles of the tomato plant. Plant Physiology 41, 119–131.
Dixon HH, Joly J.1894. On the ascent of sap. Philosophical Transactions of the Royal Society of London, Series B 186, 563–576.
Ellerby DJ, Ennos AR.1998. Resistances to fluid flow of model xylem vessels with simple and scalariform perforation plates. Journal of Experimental Botany 49, 979–85.
Gibson AC, Calkin HW, Nobel PS.1985. Hydraulic conductance and xylem structure in tracheid-bearing plants. In: Baas P, Miller RB, eds. Functional and ecological wood anatomy. Proceedings of the Martin H. Zimmermann memorial symposium, August 12, 1985. IAWA Bulletin 6, 293–302.
Giordano R, Salleo A, Salleo S, Wanderling F.1978. Flow in xylem vessels and Poiseulle's law. Canadian Journal of Botany 56, 333–338.
Grignon C, Sentenac H.1991. pH and ionic conditions in the apoplast. Annual Review of Plant Physiology and Plant Molecular Biology 42, 103–128.[ISI]
Liang JS, Zhang JH.1997. Collection of xylem sap at flow rate similar to in vivo transpiration flux. Plant and Cell Physiology 38, 1375–1381.
Milburn JA.1996. Sap ascent in vascular plants: challengers to the cohesion theory ignore the significance of immature xylem and the recycling of Munch water. Annals of Botany 78, 399–407.
Nobel PS.1983. Biophysical plant physiology and ecology. New York: WH Freeman and Company.
Pickard WF.1981. The ascent of sap in plants. Progress in Biophysics and Molecular Biology 37, 181–229.[ISI]
Schulte PJ, Castle AL.1993. Water flow through vessel perforation plates—a fluid mechanical approach. Journal of Experimental Botany 44, 1135–1142.
Schulte PJ, Gibson AC.1988. Hydraulic conductance and tracheid anatomy in six species of extant seed plants. Canadian Journal of Botany 66, 1073–109.
Schulte PJ, Gibson AC, Nobel PS.1993. The measurement of hydraulic conductance in plant stems. Proceedings of the International Conference on Measurement of Soil and Plant Water Status: in commemoration of the centennial of Utah State University, July 6–10, 1987, Logan, Utah. 2, 217–219.
Sperry JS, Donnelly JR, Tyree MT.1988. Seasonal occurrence of xylem embolism in sugar maple (Acer saccharum). American Journal of Botany 75, 1212–1218.[ISI]
Tyree MT.1997. The Cohesion–Tension theory of sap ascent: current controversies. Journal of Experimental Botany 48, 1753–1765.
Van Meeteren U, Van Gelder H.1999. Effect of time since harvest and handling conditions on rehydration ability of cut chrysanthemum flowers. Postharvest Biology and Technology 16, 169–177.
Van Meeteren U, Van Gelder H, Van Ieperen W.1999. Reconsideration of the use of deionized water as vase water in post-harvest experiments on cut flowers. Postharvest Biology and Technology 17, 175–187.
Zimmermann MH.1978. Hydraulic architecture of some diffuse-porous trees. Canadian Journal of Botany 56, 2286–2295.
Zimmermann MH.1983. Xylem structure and the ascent of sap. Berlin: Springer-Verlag.
Zimmermann MH, Jeje AA.1981. Vessel-length distribution in stems of some American woody plants. Canadian Journal of Botany 59, 1882–1992.
Zimmermann U, Haase A, Langbein D, Meinzer F.1993. Mechanisms 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 of London 341, 19–31.
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W. Van Ieperen, V. S. Volkov, and U. Van Meeteren Distribution of xylem hydraulic resistance in fruiting truss of tomato influenced by water stress J. Exp. Bot., January 2, 2003; 54(381): 317 - 324. [Abstract] [Full Text] [PDF]
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 N. M. Holbrook, M. A. Zwieniecki, and P. J. Melcher The Dynamics of "Dead Wood": Maintenance of Water Transport Through Plant Stems Integr. Comp. Biol., July 1, 2002; 42(3): 492 - 496. [Abstract] [Full Text] [PDF]
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V. Stiller and J. S. Sperry Cavitation fatigue and its reversal in sunflower (Helianthus annuus L.) J. Exp. Bot., May 1, 2002; 53(371): 1155 - 1161. [Abstract] [Full Text] [PDF]
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W. Van Ieperen, J. Nijsse, C.J. Keijzer, and U. Van Meeteren Induction of air embolism in xylem conduits of pre-defined diameter J. Exp. Bot., May 1, 2001; 52(358): 981 - 991. [Abstract] [Full Text] [PDF]
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J. Nijsse, G.W.A.M. van der Heijden, W. van Ieperen, C.J. Keijzer, and U. van Meeteren Xylem hydraulic conductivity related to conduit dimensions along chrysanthemum stems J. Exp. Bot., February 1, 2001; 52(355): 319 - 327. [Abstract] [Full Text] [PDF]
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 M. A. Zwieniecki, P. J. Melcher, and N. Michele Holbrook Hydrogel Control of Xylem Hydraulic Resistance in Plants Science, February 9, 2001; 291(5506): 1059 - 1062. [Abstract] [Full Text]
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