JXB Advance Access published online on December 16, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern299
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© 2009 The Author(s).
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RESEARCH PAPER |
Gating of aqùaporins by light and reactive oxygen species in leaf parenchyma cells of the midrib of Zea mays
Department of Plant Ecology, Bayreuth University, D-95440 Bayreuth, Germany
* To whom correspondence should be addressed. E-mail: ernst.steudle{at}uni-bayreuth.de
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, T1/2 
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 µmol m–2 s–1, T1/2 decreased during the perfusion of a control solution of 0.5 mM CaCl2 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 µmol m–2 s–1 and 1800 µmol m–2 s–1 increased the T1/2 in two-thirds of cells by factors of 14 and 35, respectively. The effects of HL on T1/2 were similar to those caused by H2O2 treatment in the presence of Fe2+, which produced ·OH (Fenton reaction; reversible oxidative gating of aquaporins). Treatments with 20 mM H2O2 following Fe2+ pre-treatments increased the T1/2 by a factor of 30. Those increased T1/2 values could be partly recovered, either when the perfusion solution was changed back to the control solutuion 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.
Key words: Aquaporin, cell pressure probe, glutathione, hydraulic conductivity, hydrogen peroxide, light, oxidative gating, reactive oxygen species, Zea mays
Received 15 July 2008; Revised 29 October 2008 Accepted 31 October 2008
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