Aquaporin gene expression and apoplastic water flow in bur oak (Quercus macrocarpa) leaves in relation to the light response of leaf hydraulic conductance

It has previously been shown that hydraulic conductance in bur oak leaves (Quercus macrocarpa Michx.), measured with the high pressure flow meter technique (HPFM), can significantly increase within 30 min following exposure to high irradiance. The present study investigated whether this increase could be explained by an increase in the cell-to-cell pathway and whether the response is linked to changes in the transcript level corresponding to aquaporin genes. Four cDNA sequences showing high similarity to members of the aquaporin gene family from other plant species were characterized from bur oak leaves and the expression levels of these cDNA sequences were examined in leaves by quantitative real-time PCR (QRT-PCR). No change was found in the relative transcript abundance corresponding to these four putative aquaporin genes in leaves with light-induced high hydraulic conductance (exposed to high irradiance) compared to leaves with low hydraulic conductance (exposed to low irradiance). However, in sun leaves that were exposed to different light levels prior to leaf collection (full sunlight, shade, and covered with aluminium foil for 16 h), the relative transcript levels of two of the putative aquaporin genes increased several-fold in shaded leaves compared to the sun-exposed or covered leaves. When the leaves were pressure-infiltrated with the apoplastic tracer dye trisodium 3-hydroxy-5,8,10-pyrenetrisulphonate (PTS3, 0.02%), there was no change in the PTS3 concentration of leaf exudates collected in ambient light or in high irradiance, but there was a small apoplastic acidification. There was also no change in PTS3 concentration between the leaves infiltrated under high irradiance with 0.02% PTS3 or with 0.1 mM HgCl2 in 0.02% PTS3. The results suggest that the putative aquaporin genes that were identified in the present study probably do not play a role in the light responses of hydraulic conductance at the transcript level, but they may function in regulating water homeostasis in leaves adapted to different light conditions. In addition, it is shown that high irradiance induced changes in the pH of the apoplast and that there does not appear to be a significant shift to the cell-to-cell mediated water transport in bur oak leaves exposed to high irradiance as measured by the apoplastic tracer dye

From Negative to Positive Integration. European State Aid Control through Soft and Hard Law

European state aid control, a part of competition policy, typically follows the logic of negative integration. It constrains the potential for Member States to distort competition by reducing their ability to subsidize industry. In addition, this paper argues, ambiguous Treaty rules and heterogeneous Member States' preferences have enabled the European Commission to act as a supranational entrepreneur, not only enforcing the prohibition of distortive state aid, but also developing its own vision of “good” state aid policy. In order to prevent or to settle political conflict about individual decisions, the Commission has sought to establish more general criteria for the state aid which it still deems admissible. These criteria have been codified into a complex system of soft law and, more recently, hard state aid law. The Commission has thus created positive integration “from above” and increasingly influences the objectives of national state aid policies