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Gating of aqùaporins by light and reactive oxygen species in leaf parenchyma cells of the midrib of Zea mays.

Kim YX, Steudle E - J. Exp. Bot. (2008)

Bottom Line: The effects of HL on T(1/2) were similar to those caused by H(2)O(2) treatment in the presence of Fe(2+), which produced *OH (Fenton reaction; reversible oxidative gating of aquaporins).The results provide evidence that the varying light climate adjusts water flow at the cell level; that is, water flow is maximized at a certain light intensity and then reduced again by HL.Light effects are discussed in terms of an oxidative gating of aquaporins by ROS.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Ecology, Bayreuth University, D-95440 Bayreuth, Germany.

ABSTRACT
Changes of the water permeability aqùaporin (AQP) activity of leaf cells were investigated in response to different light regimes (low versus high). Using a cell pressure probe, hydraulic properties (half-time of water exchange, T(1/2) infinity 1/water permeability) of parenchyma cells in the midrib tissue of maize (Zea mays L.) leaves have been measured. A new perfusion technique was applied to excised leaves to keep turgor constant and to modify the environment around cells by perfusing solutions using a pressure chamber. In response to low light (LL) of 200 micromol m(-2) s(-1), T(1/2) decreased during the perfusion of a control solution of 0.5 mM CaCl(2) by a factor of two. This was in line with earlier results from leaf cells of intact maize plants at a constant turgor. In contrast, high light (HL) at intensities of 800 micromol m(-2) s(-1) and 1800 micromol m(-2) s(-1) increased the T(1/2) in two-thirds of cells by factors of 14 and 35, respectively. The effects of HL on T(1/2) were similar to those caused by H(2)O(2) treatment in the presence of Fe(2+), which produced *OH (Fenton reaction; reversible oxidative gating of aquaporins). Treatments with 20 mM H(2)O(2) following Fe(2+) pre-treatments increased the T(1/2) by a factor of 30. Those increased T(1/2) values could be partly recovered, either when the perfusion solution was changed back to the control solution or when LL was applied. 3mM of the antioxidant glutathione also reversed the effects of HL. The data suggest that HL could induce reactive oxygen species (ROS) such as *OH, and they affected water relations. The results provide evidence that the varying light climate adjusts water flow at the cell level; that is, water flow is maximized at a certain light intensity and then reduced again by HL. Light effects are discussed in terms of an oxidative gating of aquaporins by ROS.

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Experimental set-up used. A pressure chamber was used to perfuse a leaf tissue at constant turgor pressure during illumination and to provide a particular ionic apoplastic environment. The chamber was provided with different solutions, which were infiltrated at a pressure of 0.1–0.2 MPa above atmospheric. When pressurizing the basal cut end of the xylem, guttation droplets appeared at the leaf margin and at the cut surface of the leaf outside the pressure chamber. During perfusion, water flow across the tissue was substantial, tending to exchange the solution of the apoplast within 5–20 min (see Materials and methods). A cell pressure probe was used to measure turgor and hydraulic conductivity of a cell (cell Lp). The meniscus between the cell sap and silicone oil in the probe was controlled while observing it with a stereo microscope.
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fig1: Experimental set-up used. A pressure chamber was used to perfuse a leaf tissue at constant turgor pressure during illumination and to provide a particular ionic apoplastic environment. The chamber was provided with different solutions, which were infiltrated at a pressure of 0.1–0.2 MPa above atmospheric. When pressurizing the basal cut end of the xylem, guttation droplets appeared at the leaf margin and at the cut surface of the leaf outside the pressure chamber. During perfusion, water flow across the tissue was substantial, tending to exchange the solution of the apoplast within 5–20 min (see Materials and methods). A cell pressure probe was used to measure turgor and hydraulic conductivity of a cell (cell Lp). The meniscus between the cell sap and silicone oil in the probe was controlled while observing it with a stereo microscope.

Mentions: The parenchyma cells used in the pressure probe experiments were located in the midrib region 100–200 mm behind the tip of leaves. Cells measured were located at a distance of 100–200 μm from the abaxial surface of the midrib, i.e. in the same range as those used by Kim and Steudle (2007). They usually contained no chlorophyll, but they were close to photosynthetically active cells (∼50 μm away; see cross-section in Fig. 1 of Kim and Steudle, 2007). Third or fourth leaves from the plants were used for experiments. Leaf blades were cut to a length of ∼0.3–0.4 m. About 40 mm of the leaf tip was cut and removed to enhance transport through xylem vessels by perfusion.


Gating of aqùaporins by light and reactive oxygen species in leaf parenchyma cells of the midrib of Zea mays.

Kim YX, Steudle E - J. Exp. Bot. (2008)

Experimental set-up used. A pressure chamber was used to perfuse a leaf tissue at constant turgor pressure during illumination and to provide a particular ionic apoplastic environment. The chamber was provided with different solutions, which were infiltrated at a pressure of 0.1–0.2 MPa above atmospheric. When pressurizing the basal cut end of the xylem, guttation droplets appeared at the leaf margin and at the cut surface of the leaf outside the pressure chamber. During perfusion, water flow across the tissue was substantial, tending to exchange the solution of the apoplast within 5–20 min (see Materials and methods). A cell pressure probe was used to measure turgor and hydraulic conductivity of a cell (cell Lp). The meniscus between the cell sap and silicone oil in the probe was controlled while observing it with a stereo microscope.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2651454&req=5

fig1: Experimental set-up used. A pressure chamber was used to perfuse a leaf tissue at constant turgor pressure during illumination and to provide a particular ionic apoplastic environment. The chamber was provided with different solutions, which were infiltrated at a pressure of 0.1–0.2 MPa above atmospheric. When pressurizing the basal cut end of the xylem, guttation droplets appeared at the leaf margin and at the cut surface of the leaf outside the pressure chamber. During perfusion, water flow across the tissue was substantial, tending to exchange the solution of the apoplast within 5–20 min (see Materials and methods). A cell pressure probe was used to measure turgor and hydraulic conductivity of a cell (cell Lp). The meniscus between the cell sap and silicone oil in the probe was controlled while observing it with a stereo microscope.
Mentions: The parenchyma cells used in the pressure probe experiments were located in the midrib region 100–200 mm behind the tip of leaves. Cells measured were located at a distance of 100–200 μm from the abaxial surface of the midrib, i.e. in the same range as those used by Kim and Steudle (2007). They usually contained no chlorophyll, but they were close to photosynthetically active cells (∼50 μm away; see cross-section in Fig. 1 of Kim and Steudle, 2007). Third or fourth leaves from the plants were used for experiments. Leaf blades were cut to a length of ∼0.3–0.4 m. About 40 mm of the leaf tip was cut and removed to enhance transport through xylem vessels by perfusion.

Bottom Line: The effects of HL on T(1/2) were similar to those caused by H(2)O(2) treatment in the presence of Fe(2+), which produced *OH (Fenton reaction; reversible oxidative gating of aquaporins).The results provide evidence that the varying light climate adjusts water flow at the cell level; that is, water flow is maximized at a certain light intensity and then reduced again by HL.Light effects are discussed in terms of an oxidative gating of aquaporins by ROS.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Ecology, Bayreuth University, D-95440 Bayreuth, Germany.

ABSTRACT
Changes of the water permeability aqùaporin (AQP) activity of leaf cells were investigated in response to different light regimes (low versus high). Using a cell pressure probe, hydraulic properties (half-time of water exchange, T(1/2) infinity 1/water permeability) of parenchyma cells in the midrib tissue of maize (Zea mays L.) leaves have been measured. A new perfusion technique was applied to excised leaves to keep turgor constant and to modify the environment around cells by perfusing solutions using a pressure chamber. In response to low light (LL) of 200 micromol m(-2) s(-1), T(1/2) decreased during the perfusion of a control solution of 0.5 mM CaCl(2) by a factor of two. This was in line with earlier results from leaf cells of intact maize plants at a constant turgor. In contrast, high light (HL) at intensities of 800 micromol m(-2) s(-1) and 1800 micromol m(-2) s(-1) increased the T(1/2) in two-thirds of cells by factors of 14 and 35, respectively. The effects of HL on T(1/2) were similar to those caused by H(2)O(2) treatment in the presence of Fe(2+), which produced *OH (Fenton reaction; reversible oxidative gating of aquaporins). Treatments with 20 mM H(2)O(2) following Fe(2+) pre-treatments increased the T(1/2) by a factor of 30. Those increased T(1/2) values could be partly recovered, either when the perfusion solution was changed back to the control solution or when LL was applied. 3mM of the antioxidant glutathione also reversed the effects of HL. The data suggest that HL could induce reactive oxygen species (ROS) such as *OH, and they affected water relations. The results provide evidence that the varying light climate adjusts water flow at the cell level; that is, water flow is maximized at a certain light intensity and then reduced again by HL. Light effects are discussed in terms of an oxidative gating of aquaporins by ROS.

Show MeSH