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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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Low light (LL) treatment of 200 μmol m−2 s−1 reduced T1/2, at constant turgor, as in the whole-plant experiments of Kim and Steudle (2007). (A) Cells having a T1/2 <2 s at the ambient light (AL) intensity of 50 μmol m−2 s−1 were manipulated to have a T1/2 >2 s by H2O2/Fe2+ treatment as shown in Fig. 3. The increased T1/2 was reduced by 30 min LL treatment by a factor of 7 (different letters indicate significant difference j t-test at P <0.05, n=3 cells). (B) Cells originally having a T1/2 >2 s at AL in CaCl2 solution showed a significant reduction in T1/2 during 30 min LL by a factor of 2 (P <0.05, t-test, n=4 cells). Values are means ±SD and are shown as fold changes. The absolute values of T1/2 are shown in the inset.
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fig5: Low light (LL) treatment of 200 μmol m−2 s−1 reduced T1/2, at constant turgor, as in the whole-plant experiments of Kim and Steudle (2007). (A) Cells having a T1/2 <2 s at the ambient light (AL) intensity of 50 μmol m−2 s−1 were manipulated to have a T1/2 >2 s by H2O2/Fe2+ treatment as shown in Fig. 3. The increased T1/2 was reduced by 30 min LL treatment by a factor of 7 (different letters indicate significant difference j t-test at P <0.05, n=3 cells). (B) Cells originally having a T1/2 >2 s at AL in CaCl2 solution showed a significant reduction in T1/2 during 30 min LL by a factor of 2 (P <0.05, t-test, n=4 cells). Values are means ±SD and are shown as fold changes. The absolute values of T1/2 are shown in the inset.

Mentions: When adding 20 mM H2O2 to the reference solution (0.5 mM CaCl2) at a light intensity of 50 μmol m−2 s−1, there was no effect on T1/2 (four cells tested). Most probably, this means that Fe2+ in apoplasts was not adequate to produce a sufficiently high level of ·OH (Fenton reaction; H2O2+Fe2+=Fe3++OH–+·OH). However, when the concentration of H2O2 was raised to 70 mM, T1/2 increased by a factor of 4. When perfusing with 3 mM FeSO4+0.5 mM CaCl2, T1/2s were similar to those when using only 0.5 mM CaCl2 (see above). There was a marked increase in T1/2 when 20 mM H2O2 solutions were perfused following 2 h treatments with Fe2+ (Fig. 3C). It can be seen from the figure that T1/2 increased by a factor of as much as 14 most likley due to the action of ·OH (Fig. 3C). Changing back to 0.5 mM CaCl2 again reduced T1/2 by 50% within 30 min, to a value of 700% of the original (Fig. 3D). Recovery was observed for only up to 30 min, because long-term measurements following oxidative responses and recovery in individual cells were demanding; however, there could have been further recovery during long-term measurements. It were stressed that, during measurements, turgor pressure was kept constant. Similar experiments showing inhibition by H2O2/Fe2+ treatment and partial recovery were repeated in three different cells. Overall, T1/2 increased due to the treatment by a factor of 30, and recovered to 600% of the original value within 30 min after changing back to the control perfusion solution (Fig. 4). More data showing substantial increases in T1/2 due to H2O2/FeSO4 treatment are shown for other cells in Fig. 5A (see below).


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)

Low light (LL) treatment of 200 μmol m−2 s−1 reduced T1/2, at constant turgor, as in the whole-plant experiments of Kim and Steudle (2007). (A) Cells having a T1/2 <2 s at the ambient light (AL) intensity of 50 μmol m−2 s−1 were manipulated to have a T1/2 >2 s by H2O2/Fe2+ treatment as shown in Fig. 3. The increased T1/2 was reduced by 30 min LL treatment by a factor of 7 (different letters indicate significant difference j t-test at P <0.05, n=3 cells). (B) Cells originally having a T1/2 >2 s at AL in CaCl2 solution showed a significant reduction in T1/2 during 30 min LL by a factor of 2 (P <0.05, t-test, n=4 cells). Values are means ±SD and are shown as fold changes. The absolute values of T1/2 are shown in the inset.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Low light (LL) treatment of 200 μmol m−2 s−1 reduced T1/2, at constant turgor, as in the whole-plant experiments of Kim and Steudle (2007). (A) Cells having a T1/2 <2 s at the ambient light (AL) intensity of 50 μmol m−2 s−1 were manipulated to have a T1/2 >2 s by H2O2/Fe2+ treatment as shown in Fig. 3. The increased T1/2 was reduced by 30 min LL treatment by a factor of 7 (different letters indicate significant difference j t-test at P <0.05, n=3 cells). (B) Cells originally having a T1/2 >2 s at AL in CaCl2 solution showed a significant reduction in T1/2 during 30 min LL by a factor of 2 (P <0.05, t-test, n=4 cells). Values are means ±SD and are shown as fold changes. The absolute values of T1/2 are shown in the inset.
Mentions: When adding 20 mM H2O2 to the reference solution (0.5 mM CaCl2) at a light intensity of 50 μmol m−2 s−1, there was no effect on T1/2 (four cells tested). Most probably, this means that Fe2+ in apoplasts was not adequate to produce a sufficiently high level of ·OH (Fenton reaction; H2O2+Fe2+=Fe3++OH–+·OH). However, when the concentration of H2O2 was raised to 70 mM, T1/2 increased by a factor of 4. When perfusing with 3 mM FeSO4+0.5 mM CaCl2, T1/2s were similar to those when using only 0.5 mM CaCl2 (see above). There was a marked increase in T1/2 when 20 mM H2O2 solutions were perfused following 2 h treatments with Fe2+ (Fig. 3C). It can be seen from the figure that T1/2 increased by a factor of as much as 14 most likley due to the action of ·OH (Fig. 3C). Changing back to 0.5 mM CaCl2 again reduced T1/2 by 50% within 30 min, to a value of 700% of the original (Fig. 3D). Recovery was observed for only up to 30 min, because long-term measurements following oxidative responses and recovery in individual cells were demanding; however, there could have been further recovery during long-term measurements. It were stressed that, during measurements, turgor pressure was kept constant. Similar experiments showing inhibition by H2O2/Fe2+ treatment and partial recovery were repeated in three different cells. Overall, T1/2 increased due to the treatment by a factor of 30, and recovered to 600% of the original value within 30 min after changing back to the control perfusion solution (Fig. 4). More data showing substantial increases in T1/2 due to H2O2/FeSO4 treatment are shown for other cells in Fig. 5A (see below).

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