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Excretion and folding of plasmalemma function to accommodate alterations in guard cell volume during stomatal closure in Vicia faba L.

Li B, Liu G, Deng Y, Xie M, Feng Z, Sun M, Zhao Y, Liang L, Ding N, Jia W - J. Exp. Bot. (2010)

Bottom Line: Stomatal movement results in large and repetitive changes in cell volume and consequently surface area.Additionally, an unknown structure was found at the interface between the plasmalemma and cell walls, especially in those areas of the cell where extensive folding occurred, suggesting that plasmalemma turnover is possibly associated with an interaction between the plasmalemma and cell walls.Collectively, the results strongly indicate that excretion and folding of the plasmalemma are critical for the accommodation of the cell volume alterations during stomatal movement.

View Article: PubMed Central - PubMed

Affiliation: College of Agronomy and Biotechnology, China Agricultural University, Beijing, China.

ABSTRACT
Stomatal movement results in large and repetitive changes in cell volume and consequently surface area. While endocytosis has been extensively studied and is thought to be a major mechanism for accommodating the volume changes as evidenced mainly by fluorescent labelling and confocal imaging, studies at the ultrastructural level in intact guard cells of stomata regulated by natural factors have never been reported. Here, it is reported that excretion and folding of the plasmalemma are critical for accommodating the volume alterations in intact guard cells in Vicia faba L. Using transmission electron microscopy in combination with laser confocal microscopy, it was observed that in fully opened stomata the plasmalemma was smooth and tightly adhered to the cell walls while a whole large vacuole appeared in the cell. In the closed stomata, besides vacuole fragmentation, endocytosis of the tonoplast rather than the plasmalemma commonly occurred. Importantly, in stomata where pore closure was induced by circadian rhythm or CO(2), numerous tiny vesicles were found outside the plasmalemma and, moreover, extensive folding of the plasmalemma could also be found in some regions of the cells. Additionally, an unknown structure was found at the interface between the plasmalemma and cell walls, especially in those areas of the cell where extensive folding occurred, suggesting that plasmalemma turnover is possibly associated with an interaction between the plasmalemma and cell walls. Collectively, the results strongly indicate that excretion and folding of the plasmalemma are critical for the accommodation of the cell volume alterations during stomatal movement.

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Related in: MedlinePlus

Sections of closed stomata. The stomatal closure was induced by CO2 as described in the Materials and methods. (A) A paradermal section showing a whole view of a closed stoma. Note the vacuolar fragmentation and plasmolysis (*). Bar=2 μm. (B) Magnified image of the heavily plasmolysed area. Note the small (large filled arrows) and large vesicles (large open arrows) outside the plasmalemma. The image with a large frame in the upper right corner is a enlarged view of the region with a small frame showing endocytosis. Bar=0.25 μm. (C) A paradermal section with a much higher magnification near the ventral wall showing a large number of vesicles outside the plasmalemma (large filled arrows). Bar=0.05 μm. (D) A cross-section near the central line (see Fig. 1) showing a whole view of a closed stoma. Note the plasmolysis (*). Bar=2 μm. (E) Magnified image of the framed region in D showing the relationship among plasmalemma, osmiophilic bodies, and the cell wall. Bar=0.15 μm. (F) A cross-section in the position between the central line and stomatal ledge (see Fig. 1) showing that no serious plasmolysis occurred around the cell walls. Bar=2 μm. V, vacuole; N, nucleus; SP, stomatal pore; CW, cell wall; NM, nuclear membrane; PM, plasmalemma. Bar=0.25.
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fig3: Sections of closed stomata. The stomatal closure was induced by CO2 as described in the Materials and methods. (A) A paradermal section showing a whole view of a closed stoma. Note the vacuolar fragmentation and plasmolysis (*). Bar=2 μm. (B) Magnified image of the heavily plasmolysed area. Note the small (large filled arrows) and large vesicles (large open arrows) outside the plasmalemma. The image with a large frame in the upper right corner is a enlarged view of the region with a small frame showing endocytosis. Bar=0.25 μm. (C) A paradermal section with a much higher magnification near the ventral wall showing a large number of vesicles outside the plasmalemma (large filled arrows). Bar=0.05 μm. (D) A cross-section near the central line (see Fig. 1) showing a whole view of a closed stoma. Note the plasmolysis (*). Bar=2 μm. (E) Magnified image of the framed region in D showing the relationship among plasmalemma, osmiophilic bodies, and the cell wall. Bar=0.15 μm. (F) A cross-section in the position between the central line and stomatal ledge (see Fig. 1) showing that no serious plasmolysis occurred around the cell walls. Bar=2 μm. V, vacuole; N, nucleus; SP, stomatal pore; CW, cell wall; NM, nuclear membrane; PM, plasmalemma. Bar=0.25.

Mentions: Circadian rhythm-regulated stomatal closure is a relatively slow process, which usually takes several hours or even longer. Fast stomatal closure can be induced by many natural factors such as CO2 and ABA, which may take <1 h or even several minutes when induced by high concentrations of CO2 or ABA. It was of interest to determine whether the membrane turnover in a slowly closing process may be somewhat different from that in a fast closing process. Figure 3A is a paradermal section of a stoma whose closure was induced by CO2. Surprisingly, unlike that observed in Fig. 2A, the large central vacuole fragmented into small vacuoles and, simultaneously, plasmolysis occurred more extensively, especially in the middle region of the dorsal walls (Fig. 3A). Figure 3B is a paradermal section with a higher resolution, in which it can be seen that plasmolysis occurred in the middle parts of the dorsal wall. Extensive examinations indicated that incipient plasmolysis always occurred in this place. Additionally, endocytosis can be found, but only occasionally (see the framed image). Figure 3C is a paradermal section in the dorsal wall area with an even higher resolution. Numerous tiny vesicles can again be clearly observed outside the plasmalemma. These observations demonstrate that vesicle excretion may function as an important mechanism for plasmalemma turnover. Besides plasmolysis and vesicle excretion, in cross-sections a noteworthy feature is the relationship between the osmiophilic bodies and the plasmalemma. Figure 3E is a magnified picture of the framed region in Fig. 3D. As seen in Fig. 1E, in fully opened stomata the osmiophilic bodies have oval shapes in the plasmalemma–wall interface, but in closed stomata these osmiophilic bodies have become spindly with each end connected to plasmalemma and cell wall, respectively (Fig. 3E), which appears to suggest that these osmiophilic bodies may function to adhere the plasmalemma to the cell walls, thus regulating plasmolysis. As shown in Fig. 3D, the plasmolysis is quite extensive, but in-depth examinations suggested that such an extensive plasmolysis is only confined to the central regions of the dorsal walls and sometimes the upper and lower walls. Interestingly, extensive plasmolysis never occurs in ventral walls, suggesting that the plasmolysis is regionalized. To indicate this, a cross-section taken away from the central area has been provided as Fig. 3F, from which it can be seen that the fragmented vacuoles are full of the whole cells and the plasmalemma is basically connected to the walls, although slight plasmolysis can be seen in some areas.


Excretion and folding of plasmalemma function to accommodate alterations in guard cell volume during stomatal closure in Vicia faba L.

Li B, Liu G, Deng Y, Xie M, Feng Z, Sun M, Zhao Y, Liang L, Ding N, Jia W - J. Exp. Bot. (2010)

Sections of closed stomata. The stomatal closure was induced by CO2 as described in the Materials and methods. (A) A paradermal section showing a whole view of a closed stoma. Note the vacuolar fragmentation and plasmolysis (*). Bar=2 μm. (B) Magnified image of the heavily plasmolysed area. Note the small (large filled arrows) and large vesicles (large open arrows) outside the plasmalemma. The image with a large frame in the upper right corner is a enlarged view of the region with a small frame showing endocytosis. Bar=0.25 μm. (C) A paradermal section with a much higher magnification near the ventral wall showing a large number of vesicles outside the plasmalemma (large filled arrows). Bar=0.05 μm. (D) A cross-section near the central line (see Fig. 1) showing a whole view of a closed stoma. Note the plasmolysis (*). Bar=2 μm. (E) Magnified image of the framed region in D showing the relationship among plasmalemma, osmiophilic bodies, and the cell wall. Bar=0.15 μm. (F) A cross-section in the position between the central line and stomatal ledge (see Fig. 1) showing that no serious plasmolysis occurred around the cell walls. Bar=2 μm. V, vacuole; N, nucleus; SP, stomatal pore; CW, cell wall; NM, nuclear membrane; PM, plasmalemma. Bar=0.25.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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fig3: Sections of closed stomata. The stomatal closure was induced by CO2 as described in the Materials and methods. (A) A paradermal section showing a whole view of a closed stoma. Note the vacuolar fragmentation and plasmolysis (*). Bar=2 μm. (B) Magnified image of the heavily plasmolysed area. Note the small (large filled arrows) and large vesicles (large open arrows) outside the plasmalemma. The image with a large frame in the upper right corner is a enlarged view of the region with a small frame showing endocytosis. Bar=0.25 μm. (C) A paradermal section with a much higher magnification near the ventral wall showing a large number of vesicles outside the plasmalemma (large filled arrows). Bar=0.05 μm. (D) A cross-section near the central line (see Fig. 1) showing a whole view of a closed stoma. Note the plasmolysis (*). Bar=2 μm. (E) Magnified image of the framed region in D showing the relationship among plasmalemma, osmiophilic bodies, and the cell wall. Bar=0.15 μm. (F) A cross-section in the position between the central line and stomatal ledge (see Fig. 1) showing that no serious plasmolysis occurred around the cell walls. Bar=2 μm. V, vacuole; N, nucleus; SP, stomatal pore; CW, cell wall; NM, nuclear membrane; PM, plasmalemma. Bar=0.25.
Mentions: Circadian rhythm-regulated stomatal closure is a relatively slow process, which usually takes several hours or even longer. Fast stomatal closure can be induced by many natural factors such as CO2 and ABA, which may take <1 h or even several minutes when induced by high concentrations of CO2 or ABA. It was of interest to determine whether the membrane turnover in a slowly closing process may be somewhat different from that in a fast closing process. Figure 3A is a paradermal section of a stoma whose closure was induced by CO2. Surprisingly, unlike that observed in Fig. 2A, the large central vacuole fragmented into small vacuoles and, simultaneously, plasmolysis occurred more extensively, especially in the middle region of the dorsal walls (Fig. 3A). Figure 3B is a paradermal section with a higher resolution, in which it can be seen that plasmolysis occurred in the middle parts of the dorsal wall. Extensive examinations indicated that incipient plasmolysis always occurred in this place. Additionally, endocytosis can be found, but only occasionally (see the framed image). Figure 3C is a paradermal section in the dorsal wall area with an even higher resolution. Numerous tiny vesicles can again be clearly observed outside the plasmalemma. These observations demonstrate that vesicle excretion may function as an important mechanism for plasmalemma turnover. Besides plasmolysis and vesicle excretion, in cross-sections a noteworthy feature is the relationship between the osmiophilic bodies and the plasmalemma. Figure 3E is a magnified picture of the framed region in Fig. 3D. As seen in Fig. 1E, in fully opened stomata the osmiophilic bodies have oval shapes in the plasmalemma–wall interface, but in closed stomata these osmiophilic bodies have become spindly with each end connected to plasmalemma and cell wall, respectively (Fig. 3E), which appears to suggest that these osmiophilic bodies may function to adhere the plasmalemma to the cell walls, thus regulating plasmolysis. As shown in Fig. 3D, the plasmolysis is quite extensive, but in-depth examinations suggested that such an extensive plasmolysis is only confined to the central regions of the dorsal walls and sometimes the upper and lower walls. Interestingly, extensive plasmolysis never occurs in ventral walls, suggesting that the plasmolysis is regionalized. To indicate this, a cross-section taken away from the central area has been provided as Fig. 3F, from which it can be seen that the fragmented vacuoles are full of the whole cells and the plasmalemma is basically connected to the walls, although slight plasmolysis can be seen in some areas.

Bottom Line: Stomatal movement results in large and repetitive changes in cell volume and consequently surface area.Additionally, an unknown structure was found at the interface between the plasmalemma and cell walls, especially in those areas of the cell where extensive folding occurred, suggesting that plasmalemma turnover is possibly associated with an interaction between the plasmalemma and cell walls.Collectively, the results strongly indicate that excretion and folding of the plasmalemma are critical for the accommodation of the cell volume alterations during stomatal movement.

View Article: PubMed Central - PubMed

Affiliation: College of Agronomy and Biotechnology, China Agricultural University, Beijing, China.

ABSTRACT
Stomatal movement results in large and repetitive changes in cell volume and consequently surface area. While endocytosis has been extensively studied and is thought to be a major mechanism for accommodating the volume changes as evidenced mainly by fluorescent labelling and confocal imaging, studies at the ultrastructural level in intact guard cells of stomata regulated by natural factors have never been reported. Here, it is reported that excretion and folding of the plasmalemma are critical for accommodating the volume alterations in intact guard cells in Vicia faba L. Using transmission electron microscopy in combination with laser confocal microscopy, it was observed that in fully opened stomata the plasmalemma was smooth and tightly adhered to the cell walls while a whole large vacuole appeared in the cell. In the closed stomata, besides vacuole fragmentation, endocytosis of the tonoplast rather than the plasmalemma commonly occurred. Importantly, in stomata where pore closure was induced by circadian rhythm or CO(2), numerous tiny vesicles were found outside the plasmalemma and, moreover, extensive folding of the plasmalemma could also be found in some regions of the cells. Additionally, an unknown structure was found at the interface between the plasmalemma and cell walls, especially in those areas of the cell where extensive folding occurred, suggesting that plasmalemma turnover is possibly associated with an interaction between the plasmalemma and cell walls. Collectively, the results strongly indicate that excretion and folding of the plasmalemma are critical for the accommodation of the cell volume alterations during stomatal movement.

Show MeSH
Related in: MedlinePlus