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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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In the presence of the antioxidant glutathione (GSH), the effects of HL treatment at 1800 μmol m−2 s−1 could be reversed. Cells pre-treated with 3 mM GSH+0.5 mM CaCl2 for 0.5–1.0 h (black bars, n=4 cells) had an increased T1/2 due to HL as in the absence of GSH (as in Fig. 5). In the presence of GSH, in contrast, there was a recovery within 15 min after the light was switched off. Cells pre-treated with GSH for 24 h (grey bars, n=5 cells) did not show an increase in T1/2 by HL (P <0.05, t-test). 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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fig7: In the presence of the antioxidant glutathione (GSH), the effects of HL treatment at 1800 μmol m−2 s−1 could be reversed. Cells pre-treated with 3 mM GSH+0.5 mM CaCl2 for 0.5–1.0 h (black bars, n=4 cells) had an increased T1/2 due to HL as in the absence of GSH (as in Fig. 5). In the presence of GSH, in contrast, there was a recovery within 15 min after the light was switched off. Cells pre-treated with GSH for 24 h (grey bars, n=5 cells) did not show an increase in T1/2 by HL (P <0.05, t-test). Values are means ±SD and are shown as fold changes. The absolute values of T1/2 are shown in the inset.

Mentions: Cells pre-treated with the antioxidant GSH were exposed to a 15 min period of illumination at the intensity of 1800 μmol m−2 s−1. As seen in Fig. 7, a cell which had been perfused with 3 mM GSH+0.5 mM CaCl2 for 0.5–1.0 h increased its T1/2 by a factor of 46 by HL, as in the absence of GSH. However, in the presence of GSH, T1/2 recovered back to its original level within 15 min when the light was turned off (n=5 cells). This was different from treatment in the absence of GSH. Pre-treatment with 3 mM GSH of 24 h duration had pronounced ameliorative effects. In contrast to short treatments, T1/2s showed no significant increase with HL (n=4 cells). To confirm that the lack of response was due to the presence of GSH rather than a coincidence originating from the variable responses between cells (one-third of cells did not react to HL; see above), by following one cell tests were conducted to determine whether the T1/2 in control solution increased in response to HL, and then that the addition of GSH caused recovery of the T1/2 to its original value. On the same cell, light treatment in the presence of GSH caused only a temporary increase in T1/2, which eventually recovered to the original value at the ambient light intensity (data not shown). In the reverse type of experiment using 3 mM GSH, there was no response of the T1/2 by 15 min HL treatment following treatment with 3 mM GSH solution for 3 h. On the same cell, the exchange of GSH solution by the reference solution and waiting for its complete removal (∼1 h) caused a substantial increase of T1/2 by 15 min HL treatment (data not shown). Overall, the results indicate that there was a clear ameliorative effect of GSH on cell Lp (T1/2). It is unlikely that the effect of the GSH solution is due to changes in pH (from 4.8 to 3.5), since cytosolic acidification is known to reduce water permeability by a gating of AQPs (Tournaire-Roux C et al., 2003). The effects of HL may be related to oxidative stress in the presence of HL (see Discussion).


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)

In the presence of the antioxidant glutathione (GSH), the effects of HL treatment at 1800 μmol m−2 s−1 could be reversed. Cells pre-treated with 3 mM GSH+0.5 mM CaCl2 for 0.5–1.0 h (black bars, n=4 cells) had an increased T1/2 due to HL as in the absence of GSH (as in Fig. 5). In the presence of GSH, in contrast, there was a recovery within 15 min after the light was switched off. Cells pre-treated with GSH for 24 h (grey bars, n=5 cells) did not show an increase in T1/2 by HL (P <0.05, t-test). 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

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getmorefigures.php?uid=PMC2651454&req=5

fig7: In the presence of the antioxidant glutathione (GSH), the effects of HL treatment at 1800 μmol m−2 s−1 could be reversed. Cells pre-treated with 3 mM GSH+0.5 mM CaCl2 for 0.5–1.0 h (black bars, n=4 cells) had an increased T1/2 due to HL as in the absence of GSH (as in Fig. 5). In the presence of GSH, in contrast, there was a recovery within 15 min after the light was switched off. Cells pre-treated with GSH for 24 h (grey bars, n=5 cells) did not show an increase in T1/2 by HL (P <0.05, t-test). Values are means ±SD and are shown as fold changes. The absolute values of T1/2 are shown in the inset.
Mentions: Cells pre-treated with the antioxidant GSH were exposed to a 15 min period of illumination at the intensity of 1800 μmol m−2 s−1. As seen in Fig. 7, a cell which had been perfused with 3 mM GSH+0.5 mM CaCl2 for 0.5–1.0 h increased its T1/2 by a factor of 46 by HL, as in the absence of GSH. However, in the presence of GSH, T1/2 recovered back to its original level within 15 min when the light was turned off (n=5 cells). This was different from treatment in the absence of GSH. Pre-treatment with 3 mM GSH of 24 h duration had pronounced ameliorative effects. In contrast to short treatments, T1/2s showed no significant increase with HL (n=4 cells). To confirm that the lack of response was due to the presence of GSH rather than a coincidence originating from the variable responses between cells (one-third of cells did not react to HL; see above), by following one cell tests were conducted to determine whether the T1/2 in control solution increased in response to HL, and then that the addition of GSH caused recovery of the T1/2 to its original value. On the same cell, light treatment in the presence of GSH caused only a temporary increase in T1/2, which eventually recovered to the original value at the ambient light intensity (data not shown). In the reverse type of experiment using 3 mM GSH, there was no response of the T1/2 by 15 min HL treatment following treatment with 3 mM GSH solution for 3 h. On the same cell, the exchange of GSH solution by the reference solution and waiting for its complete removal (∼1 h) caused a substantial increase of T1/2 by 15 min HL treatment (data not shown). Overall, the results indicate that there was a clear ameliorative effect of GSH on cell Lp (T1/2). It is unlikely that the effect of the GSH solution is due to changes in pH (from 4.8 to 3.5), since cytosolic acidification is known to reduce water permeability by a gating of AQPs (Tournaire-Roux C et al., 2003). The effects of HL may be related to oxidative stress in the presence of HL (see Discussion).

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
Related in: MedlinePlus