Stomata closure under adverse conditions leads to reduced CO2 assimilation and yield penalty. This review focuses on advances in stomata research especially for crops growing at hyperosmotic saline environments. Possible new aspects of nutritional imbalances under saline hyperosmotic conditions on guard cell metabolism which were deduced from the recent literature were focused. In particular possible effects of high Na+ concentration on GABA shunt which may regulate tonoplast anion channel activity and thus stomatal aperture were discussed. The extent to which stress-induced GABA production influences stomatal behavior in interaction with other signaling pathways remains an interesting topic that requires further research. Another example is magnesium and its role in stomata regulation. Up to date understanding about the relevance of a salinity-induced reduction of magnesium for stomatal opening is rudimentary. Few reports have linked the magnesium-nutritional status to transpiration, doing so by contemplating a role of mesophyll-derived CO2- or sugar-signals. Further research is needed to test whether stomatal opening is delayed when photosynthetic electron transport or the ability to extrude protons are impaired due to salinity-induced deficiency of magnesium. Furthermore, we discuss an opinion that sulfur might be involved in guard cell regulation in crop plants. Our article may provoke further research to broaden the knowledge of the underlying guard cell physiology.

Background and Aims Viticulture will be particularly affected by increasing drought and heat waves in the future. It is of interest to find traits that indicate stress before symptoms become apparent. We investigated whether the commonly used traits, proline and abscisic acid (ABA) biosynthesis, are suitable markers for heat, drought or combined stress and whether gene expression of key enzymes of ABA biosynthesis is regulated in grapevine leaves under these stress conditions. Methods and Results Plant growth and gas exchange were measured to evaluate plant reactions to increased temperature and water deficit. Proline and ABA concentration in leaf material was measured, respectively, photometrically and with GC/MS. Gene expression analysis of NCED1, NCED2 and P5CS was done by real-time quantitative reverse transcription-polymerase chain reaction. Drought stress had a stronger effect on growth, gas exchange, proline, and ABA biosynthesis than heat stress. An interaction between heat and drought stress was observed for gas exchange and for proline biosynthesis. Conclusions Proline concentration and gene expression of P5CS are good markers for combined stress. The concentration of ABA is a suitable marker for drought stress and might be a suitable marker for combined stress. Gene expression of NCED1 in leaves was a good marker for drought stress and might be a suitable marker for combined stress, whereas NCED2 was not suitable. Significance of the Study These results provide insight into the response of grapevines to heat, drought and combined stress and show the suitability of ABA and proline as stress markers.

Training systems are an option to handle the pronounced apical dominance of grapevines and to influence diverse traits of the corresponding wine. However, it is still unclear if different training systems generate signatures in the metabolome of the wine. By an untargeted metabolomics approach using (SPME) GC-MS wine (volatiles) and leaves were evaluated. Different training directions such as vertical shoot positioning systems, hanging shoot systems, and minimal pruning systems were distinguishable in wine. It was shown, that different training systems generate a metabolomic signature in the wine which was more pronounced than in leaves. Moreover, the sensory analysis showed some changes in the aroma of the different training systems. Thus, the influence of the training system ranges from the leaf metabolome to the wine metabolome.