Glutamate dehydrogenase (GDH) may be a stress-responsive enzyme, as GDH exhibits considerable thermal stability, and de novo synthesis of the α-GDH subunit is induced by exogenous ammonium and senescence. NaCl treatment induces reactive oxygen species (ROS), intracellular ammonia, expression of tobacco (Nicotiana tabacum cv Xanthi) gdh-NAD;A1 encoding the α-subunit of GDH, increase in immunoreactive α-polypeptide, assembly of the anionic isoenzymes, and in vitro GDH aminating activity in tissues from hypergeous plant organs. In vivo aminating GDH activity was confirmed by gas chromatorgraphy–mass spectrometry monitoring of ¹⁵N-Glu, ¹⁵N-Gln, and ¹⁵N-Pro in the presence of methionine sulfoximine and amino oxyacetic acid, inhibitors of Gln synthetase and transaminases, respectively. Along with upregulation of α-GDH by NaCl, isocitrate dehydrogenase genes, which provide 2-oxoglutarate, are also induced. Treatment with menadione also elicits a severalfold increase in ROS and immunoreactive α-polypeptide and GDH activity. This suggests that ROS participate in the signaling pathway for GDH expression and protease activation, which contribute to intracellular hyperammonia. Ammonium ions also mimic the effects of salinity in induction of gdh-NAD;A1 expression. These results, confirmed in tobacco and grape (Vitis vinifera cv Sultanina) tissues, support the hypothesis that the salinity-generated ROS signal induces α-GDH subunit expression, and the anionic iso-GDHs assimilate ammonia, acting as antistress enzymes in ammonia detoxification and production of Glu for Pro synthesis.

This paper provides an overview of the Special Issue on water supply and water scarcity. The papers selected for publication include review papers on water history, on water management issues under water scarcity regimes, on rainwater harvesting, on water quality and degradation, and on climatic variability impacts on water resources. Overall, the issue underscores the need for a revised water management, especially in areas with demographic change and climate vulnerability towards sustainable and secure water supply. Moreover, general guidelines and possible solutions, such as the adoption of advanced technological solutions and practices that improve water use efficiency and the use of alternative (non-conventional) water resources are highlighted and discussed to address growing environmental and health issues and to reduce the emerging conflicts among water users.

Water quality criteria are an indispensable part of water reuse projects aiming to ensure the protection of public health and the environment. In addition, criteria can affect the development, public acceptance, and economic viability of water reuse projects. Currently no uniform criteria exist, but they diverge, often greatly, between countries and states. The authors briefly present the evolution of reuse criteria worldwide and discuss emerging issues related to ecological and public health risks that have not addressed adequately in existing criteria. They specifically focus on European Union (EU) countries and present their water reuse status based on the published data and the existing (or nonexisting) reuse frameworks. Data gathered from public agencies reveal a high potential for water reuse in the EU that could potentially contribute to ensuring that fresh water is available for all sectors and to protect the environment, but it has not expanded at the expected rates. The lack of water reuse criteria was thought as the most important cause for this delay. lasting recent years, however, several countries, particularly those located in the Mediterranean basin, established water reuse criteria. Similarities and differences as well as potential benefits and drawbacks of these criteria are discussed and interpreted with these of the other world. An important conclusion is that the criteria enacted in Greece, Italy, and Spain will probably prevent the development of water reuse projects and increase the costs. Moreover, major challenges, the future views, and the necessity for establishing common regulations for water reuse at an EU level are considered.