Limits...
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.

Show MeSH
Representative relaxation curves used to measure half-times of water exchange, T1/2s. (A) The half-time of cells from excised leaves which were perfused with 0.5 mM CaCl2 typically ranged between 1.0 s and 2.0 s. A reversible oxidative gating of AQPs was demonstrated by following an individual cell in B to D. (B) Half-times of cells in the presence of Fe2+ were similar to those in CaCl2 and this was used as the control. (C) On the same cell as in B, addition of 20 mM H2O2 produced OH· by the Fenton reaction and caused a substantial increase in T1/2 by a factor of 27, i.e. Lp was reduced by the same factor. (D) Subsequent exchange to 0.5 mM CaCl2 to remove radicals resulted in a partial recovery of T1/2 (Lp), i.e. the effect was reversible, at least to some extent.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig3: Representative relaxation curves used to measure half-times of water exchange, T1/2s. (A) The half-time of cells from excised leaves which were perfused with 0.5 mM CaCl2 typically ranged between 1.0 s and 2.0 s. A reversible oxidative gating of AQPs was demonstrated by following an individual cell in B to D. (B) Half-times of cells in the presence of Fe2+ were similar to those in CaCl2 and this was used as the control. (C) On the same cell as in B, addition of 20 mM H2O2 produced OH· by the Fenton reaction and caused a substantial increase in T1/2 by a factor of 27, i.e. Lp was reduced by the same factor. (D) Subsequent exchange to 0.5 mM CaCl2 to remove radicals resulted in a partial recovery of T1/2 (Lp), i.e. the effect was reversible, at least to some extent.

Mentions: From the pressure relaxations, Lp values could be worked out, when the elastic modulus (ε) was also measured. However, in most cases, T1/2s (inversely proportional to cell Lp) were taken as a measure of cell Lp because ε did not change during treatments for a given cell (Kim and Steudle, 2007). In most cases, there was no transient effect of puncturing on T1/2 (Lp) as observed with young maize roots (Wan et al., 2004). When there was such an effect, it took 10 min, which was sufficient to achieve a constant T1/2. At the ambient light intensity of 50 μmol m−2 s−1, the T1/2s of cells from leaves infiltrated with 0.5 mM CaCl2 ranged from 0.3 s to 35 s (mean±SD, 4.8±7.7 s, n=31 cells; Fig. 2). The variability of T1/2 was also known in the same tissue of intact maize plants (Kim and Steudle, 2007). However, >75% of those cells (24 out of 31 cells with 0.5 mM CaCl2) had T1/2s of <4 s, and one-third of cells had T1/2s between 1.0 s and 2.0 s (12 out of 31 cells; Figs 2, 3A). Cells infiltrated with 0.5 mM CaCl2/3 mM FeSO4 had T1/2s similar to those infiltrated with 0.5 mM CaCl2 (range=0.8–17 s; mean±SD, 3.6±3.8 s, n=24 cells; 21 out of 24 cells had a T1/2 <4 s; Figs 2, 3B). Usually, cells probed from one leaf had similar T1/2s. For example, six cells probed from the same leaf had T1/2s ranging from 0.9 s to 2.3 s. The large T1/2s occasionally measured were observed in a few leaves and they were probably caused by a closure of AQPs, even in the absence of inhibitors or HL. Those T1/2s could be reduced by light treatment of up to 650 μmol m−2 s−1, according to the earlier results of Kim and Steudle (2007).


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)

Representative relaxation curves used to measure half-times of water exchange, T1/2s. (A) The half-time of cells from excised leaves which were perfused with 0.5 mM CaCl2 typically ranged between 1.0 s and 2.0 s. A reversible oxidative gating of AQPs was demonstrated by following an individual cell in B to D. (B) Half-times of cells in the presence of Fe2+ were similar to those in CaCl2 and this was used as the control. (C) On the same cell as in B, addition of 20 mM H2O2 produced OH· by the Fenton reaction and caused a substantial increase in T1/2 by a factor of 27, i.e. Lp was reduced by the same factor. (D) Subsequent exchange to 0.5 mM CaCl2 to remove radicals resulted in a partial recovery of T1/2 (Lp), i.e. the effect was reversible, at least to some extent.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig3: Representative relaxation curves used to measure half-times of water exchange, T1/2s. (A) The half-time of cells from excised leaves which were perfused with 0.5 mM CaCl2 typically ranged between 1.0 s and 2.0 s. A reversible oxidative gating of AQPs was demonstrated by following an individual cell in B to D. (B) Half-times of cells in the presence of Fe2+ were similar to those in CaCl2 and this was used as the control. (C) On the same cell as in B, addition of 20 mM H2O2 produced OH· by the Fenton reaction and caused a substantial increase in T1/2 by a factor of 27, i.e. Lp was reduced by the same factor. (D) Subsequent exchange to 0.5 mM CaCl2 to remove radicals resulted in a partial recovery of T1/2 (Lp), i.e. the effect was reversible, at least to some extent.
Mentions: From the pressure relaxations, Lp values could be worked out, when the elastic modulus (ε) was also measured. However, in most cases, T1/2s (inversely proportional to cell Lp) were taken as a measure of cell Lp because ε did not change during treatments for a given cell (Kim and Steudle, 2007). In most cases, there was no transient effect of puncturing on T1/2 (Lp) as observed with young maize roots (Wan et al., 2004). When there was such an effect, it took 10 min, which was sufficient to achieve a constant T1/2. At the ambient light intensity of 50 μmol m−2 s−1, the T1/2s of cells from leaves infiltrated with 0.5 mM CaCl2 ranged from 0.3 s to 35 s (mean±SD, 4.8±7.7 s, n=31 cells; Fig. 2). The variability of T1/2 was also known in the same tissue of intact maize plants (Kim and Steudle, 2007). However, >75% of those cells (24 out of 31 cells with 0.5 mM CaCl2) had T1/2s of <4 s, and one-third of cells had T1/2s between 1.0 s and 2.0 s (12 out of 31 cells; Figs 2, 3A). Cells infiltrated with 0.5 mM CaCl2/3 mM FeSO4 had T1/2s similar to those infiltrated with 0.5 mM CaCl2 (range=0.8–17 s; mean±SD, 3.6±3.8 s, n=24 cells; 21 out of 24 cells had a T1/2 <4 s; Figs 2, 3B). Usually, cells probed from one leaf had similar T1/2s. For example, six cells probed from the same leaf had T1/2s ranging from 0.9 s to 2.3 s. The large T1/2s occasionally measured were observed in a few leaves and they were probably caused by a closure of AQPs, even in the absence of inhibitors or HL. Those T1/2s could be reduced by light treatment of up to 650 μmol m−2 s−1, according to the earlier results of Kim and Steudle (2007).

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