Article Figures & Data
Figures
- Figure 1.
P. nigra PLC in relation to stem water potential. Data were fitted with a dose-response curve (solid line) in the form of PLC = minPLC + (maxPLC − minPLC)/(1 + (Ψ/EC50)slope), where minPLC is minimum PLC in nonstressed plants (49.1%), maxPLC is 100%, EC50 represents 50% loss of initial functionality [minPLC + (maxPLC − minPLC)/2], and slope is the rate of PLC increase at EC50. The dashed lines represent the 95% confidence interval for the fit. PLC of plants recovering from stress was not used in the fitting procedure. [See online article for color version of this figure.]
- Figure 2.
Analysis of water volume in functional and nonfunctional vessels of P. nigra in relation to water stress level.
- Figure 3.
Changes in the osmotic potential of liquid collected from functional (A) and nonfunctional (B) vessels in relation to stem water potential (balancing pressure at the time of sample collection). Total osmotic potential (π) was determined using isopiestic psychrometric measurements. Estimation of π from sugar was calculated as the equivalent of Glc content and that of π from ions as the equivalent of K+ ion concentration. The dashed line represents a 1:1 relation between balancing pressure and osmotic potential of liquid.
- Figure 4.
Osmotic potential of liquid collected from functional and nonfunctional vessels of plants recovering from moderate stress (−2.0 < Ψ < 1.0 MPa). Total osmotic potential (π) of liquid collected from nonfunctional vessels was significantly higher than that collected from functional vessels (Student’s t test, P < 0.001). The composition of the osmoticum also differed between two water sources, with ions being a major component in functional vessels and an equal importance of sugars and ions in nonfunctional vessels. [See online article for color version of this figure.]
- Figure 5.
Relationship between xylem sap pH and stem water potential. Sap from functional vessels was fitted with a dose-response curve: pH = minpH + (maxpH − minpH)/(1 + (Ψ/EC50)slope), where maxpH = 6.26, minpH = 3.42, EC50 = −1.43, and slope = 10 (r2 = 0.71). The volume of liquid collected from nonfunctional vessels of severely stressed plants was not enough to measure pH. No obvious relationship between pH and plant water stress was found for liquid from nonfunctional vessels from a linear fit (r2 = 0.01).
- Figure 6.
Schematic illustration of the membrane-level physiology of refilling. See text for explanation. Red arrows represent fluxes. Blue arrows represent action/influence. Green stars represent information available from previous studies. Red stars represent new information from our analysis. [See online article for color version of this figure.]
- Figure 7.
Schematics present the technical steps involved in collecting sap from nonfunctional vessels. 1, An intact plant with functional vessels under tension (a and c) and a nonfunctional vessel partially filled with water (b). 2, Collection starts with the first cut made in the air. This would allow water under tension to be sucked toward the leaves in vessels a and c but not the water present in vessel b. In vessel c, water would only be sucked to the nearest border pit field. 3, Within several seconds following the first cut, a second cut is made and a portion of stem (3–4 cm) long is removed. It presumably contains some water under tension stuck on the bordered pit field (c) and water in nonfunctional vessels. 4, The section is then inverted and both ends are fitted to flexible tubes. 5, The upper tube is then filled with low-viscosity silicon oil and the lower end is fitted to a vacuum system. 6, A vacuum is generated that sucks oil through the empty vessels (a) and vessels that are open across the stem but filled with water droplets (b). However, the vacuum is not adequate to break water away from the border pit field (c). Oil containing small volumes of water from nonfunctional vessels is collected in centrifuge tubes and protects small droplets from evaporation in vacuum conditions. After several collection cycles, centrifuge tubes are spun and water is separated from oil at the bottom of the tube. Arrows and flat-ended lines represent the movement of water in vessels during the procedure of water collection.
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Supplemental Data
Supplemental Figure
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