- Water permeability of plant cells measured by pressure probes: effects of light and turgor, and the role of unstirred layers (2008)
- The dissertation focuses (i) on an analysis of effects of unstirred layers (USLs) during measurements of water permeability (hydraulic conductivity) at the level of single cells, during measurements with the cell pressure probe (CPP) and (ii) on the use of the latter technique to investigate changes in water permeability of leaf cells in response to light. Internodes of the giant green alga Chara corallina and parenchyma cells of corn leaves were used in the studies. Besides the water, the CPP has been employed to study solute flows across cell membranes. This allowed evaluating the role of different types of USLs. In response to claims, recently raised by Tyree et al. (2005) that USLs play a significant or even dominating role in measurements of transport coefficients with the cell pressure probe, a rigorous re-examination of effects of USLs with Chara internodes has been performed indicating a minor role of USLs. For the first time, responses of cell water relations to light have been worked in some detail. Light effects have been separated from those of turgor in intact tissue cells by compensating for transpiration. At low light (LL) intensity (100 to 650 micromol m-2 s-1), hydraulic conductivity of a cell (cell Lp) increased with increasing light intensity by a factor of 2 to 6 in 10 min. However, at high light (HL) intensities of 800 and 1800 micromol m-2 s-1, there was a decline of cell Lp with increasing light intensity at constant cell turgor by factors of 14 and 35, respectively. The effects of LL refer to literature data of overall measurements of the leaf conductances (Kleaf). Decreases of Kleaf at HL have not yet been separated for effects of turgor or light intensity, respectively (as done here). The responses to HL were most likely caused by an oxidative gating of water channels (aquaporins; AQPs), as indicated by the fact that (i) application of reactive oxygen species (ROS) resulted in responses similar to those of HL and (ii) HL effects could be reversed in the presence of the antioxidant glutathione. For the first time, the data indicate an interaction between water relations and light intensity/photosynthesis, which is most likely related to changes in the redox status of leaves.