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Using a different shoot of T. usneoides, a layer of Vaseline was applied as a hydrophobic barrier to prevent external water flow on the stem, without, however, affecting any potential internal flow of water via the xylem or mesophyll (Figure 5). After immersing the cut end of the shoot into water, water was transported on the stem's surface toward the border of the Vaseline-treated area, but not beyond (Figure 5b). This indicated that water was only transported externally on the stem and not inside the stem/leaf. Pos 3 sod yaseline Pos 2 1 mm (a) Pos 1

Using a different shoot of T. usneoides, a layer of Vaseline was applied as a hydrophobic barrier to prevent external water flow on the stem, without, however, affecting any potential internal flow of water via the xylem or mesophyll (Figure 5). After immersing the cut end of the shoot into water, water was transported on the stem's surface toward the border of the Vaseline-treated area, but not beyond (Figure 5b). This indicated that water was only transported externally on the stem and not inside the stem/leaf. Pos 3 sod yaseline Pos 2 1 mm (a) Pos 1

BIOLOGY:CONCEPTS+APPL.(LOOSELEAF)
BIOLOGY:CONCEPTS+APPL.(LOOSELEAF)
10th Edition
ISBN:9781305967359
Author:STARR
Publisher:STARR
Chapter25: Plant Tissues
Section: Chapter Questions
Problem 11SA
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Based on the information explain the figure
Using a different shoot of T. usneoides, a layer of Vaseline was applied as a hydrophobic barrier to prevent external water flow on the stem, without, however, affecting any potential internal flow of water via the xylem or mesophyll (Figure 5). After immersing the cut end of the shoot into water, water was transported on the stem's surface toward the border of the Vaseline-treated area, but not beyond (Figure 5b). This indicated that water was only transported externally on the stem and not inside the stem/leaf. Pos Pos 4 Vaseline Pos 2 mm (a) Pos 1 70 Pos 1 Pos 2 Pos 3 Pos 4 50 60- (d) (c) Pos3 Pos 4 200 600 800 1000 Distance, mm Time. s Figure 5 Open in figure viewer +PowerPoint Application of Vaseline to block external water flow on shoots of Tillandsia usneoides. (a) The part of the shoot Change o (water thickness, um)
Transcribed Image Text:Using a different shoot of T. usneoides, a layer of Vaseline was applied as a hydrophobic barrier to prevent external water flow on the stem, without, however, affecting any potential internal flow of water via the xylem or mesophyll (Figure 5). After immersing the cut end of the shoot into water, water was transported on the stem's surface toward the border of the Vaseline-treated area, but not beyond (Figure 5b). This indicated that water was only transported externally on the stem and not inside the stem/leaf. Pos Pos 4 Vaseline Pos 2 mm (a) Pos 1 70 Pos 1 Pos 2 Pos 3 Pos 4 50 60- (d) (c) Pos3 Pos 4 200 600 800 1000 Distance, mm Time. s Figure 5 Open in figure viewer +PowerPoint Application of Vaseline to block external water flow on shoots of Tillandsia usneoides. (a) The part of the shoot Change o (water thickness, um)
The observation that water was exclusively transported on the stem surface was, furthermore, corroborated by transmission profiles across the shoot (Figure 5c) that are in line with the transmission pattern calculated by the simplified film transport model (c.f. Figure 2b). The water front occurred at the respective position 90 s (Pos 1), 250 s (Pos 2), and 500 s (Pos 3) after immersing the cut end of the shoot into water. At Pos 4, however, past the area where the stem was covered with Vaseline, transmission did not change, indicating that water moved exclusively on the exterior surface but not through the vascular system inside the stem. Furthermore, according to Equation 2, a water-filled tracheid with a diameter of 6.4 µm would attenuate the incident neutron beam by about 0.3%. Quotient imaging as used in these studies iŞ very sensitive to changes in water thickness and, consequently, should have been able to detect even small changes due to water transported by a few very small tracheids. Indeed, mean tracheid diameter in this species is quite narrow (e.g., Cheadle, 1955; Males, 2016). Moreover, on its way through the sample, the beam traversed several tracheids. The detected attenuation signal is then the sum of individual attenuation by the tracheids aligned in beam directions. If a significant amount of water was transported via the xylem, this would have been clearly detected by the technique applied. The restriction of the spread of water to the stem surface was also documented by the evolution of neutron transmission observed at different positions of the shoot (Figure 5d). The onset of transmission decrease indicated the arrival of the water front at each respective position. About 10 min after immersing the cut end into water, the water front arrived at Position 3 on the shoot indicating that the rate of liquid water movement by capillarity between the undersurfaces of the trichome wings, and the outer epidermis of the shoots was approximately 0.03 mm s-1. Although this value is lower than xylem flow velocities typically reported in the literature (0.05 mm s-1 and 280 mm s1, depending on species, growth form, and environmental conditions; e.g., Peuke, Rokitta, Zimmermann, Schreiber, & Haase, 2001), it compares with xylem water movement of tomato plants (0.01 mm s-1; Matsushima et al., 2008) or plants of different rose cultivars (ranging between 0.005 and 0.02 mm s-1; Matsushima, Herppich, et al., 2009; Matsushima, Graf, et al., 2009) also measured at low light and free convection, that is, under similar low-transpiration
Transcribed Image Text:The observation that water was exclusively transported on the stem surface was, furthermore, corroborated by transmission profiles across the shoot (Figure 5c) that are in line with the transmission pattern calculated by the simplified film transport model (c.f. Figure 2b). The water front occurred at the respective position 90 s (Pos 1), 250 s (Pos 2), and 500 s (Pos 3) after immersing the cut end of the shoot into water. At Pos 4, however, past the area where the stem was covered with Vaseline, transmission did not change, indicating that water moved exclusively on the exterior surface but not through the vascular system inside the stem. Furthermore, according to Equation 2, a water-filled tracheid with a diameter of 6.4 µm would attenuate the incident neutron beam by about 0.3%. Quotient imaging as used in these studies iŞ very sensitive to changes in water thickness and, consequently, should have been able to detect even small changes due to water transported by a few very small tracheids. Indeed, mean tracheid diameter in this species is quite narrow (e.g., Cheadle, 1955; Males, 2016). Moreover, on its way through the sample, the beam traversed several tracheids. The detected attenuation signal is then the sum of individual attenuation by the tracheids aligned in beam directions. If a significant amount of water was transported via the xylem, this would have been clearly detected by the technique applied. The restriction of the spread of water to the stem surface was also documented by the evolution of neutron transmission observed at different positions of the shoot (Figure 5d). The onset of transmission decrease indicated the arrival of the water front at each respective position. About 10 min after immersing the cut end into water, the water front arrived at Position 3 on the shoot indicating that the rate of liquid water movement by capillarity between the undersurfaces of the trichome wings, and the outer epidermis of the shoots was approximately 0.03 mm s-1. Although this value is lower than xylem flow velocities typically reported in the literature (0.05 mm s-1 and 280 mm s1, depending on species, growth form, and environmental conditions; e.g., Peuke, Rokitta, Zimmermann, Schreiber, & Haase, 2001), it compares with xylem water movement of tomato plants (0.01 mm s-1; Matsushima et al., 2008) or plants of different rose cultivars (ranging between 0.005 and 0.02 mm s-1; Matsushima, Herppich, et al., 2009; Matsushima, Graf, et al., 2009) also measured at low light and free convection, that is, under similar low-transpiration
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