Cell-specific analysis of spatial ion patterns of stomata under salinity in two salt sensitve crops

• Applicant: Professor Dr. Christian Zörb
• Subject Area: Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491678431

The improvement of salt tolerance of crop plants represents a task of increasing relevance. Faba bean is sensitive to high salt, in particular to chloride, leading to severe growth reductions. In comparison, maize is moderately sensitive to NaCl and Cl-. We aim to analyse the interplay between tissue tolerance and stomata related processes contributing to salt tolerance under conditions of increased salt ion concentrations in leaves. Because stomatal function is a top-down regulator of many physiological processes, dysfunctions of stomata inevitably have severe detrimental effects on plant growth and development. Therefore, maintaining guard cell functionality and thereby control of the water status of plants will result in an improved performance under salinity. The stomatal complex of maize differs to that of faba bean, because monocot guard cells are surrounded by subsidiary cells, which function as a reservoir for inorganic ions. In faba bean, the cell wall, i.e. the apoplast fulfils the corresponding function. Because guard cells have poor selectivity for K+ over other monovalent cations such as Na+ and import Cl- in dependency of its concentrations in the cell walls, harmful accumulation of Na+ and Cl- ions in guard cells, might occur under conditions of NaCl exposure. This observation received only little attention to date but is potentially of tremendous significance for growth performance under stress because stomata are openings on leaf surfaces that regulate intake of CO2 for photosynthesis and water loss through transpiration. The reduction of stomatal aperture under salt induced (water) stress is an effective adjustment to salinity that must be necessarily maintained. Effects of ionic stress on guard cells are merely studied. Most studies are based on whole leaves and, thus, do not have the basis to provide new insights into guard cell stress responses and, in particular, upon effects of salt enrichment in the guard cell walls. Our recent pilot experiments on epidermal peels suggested that some of the Na+ and Cl- is taken up into guard cells under long term NaCl stress. When Na+ and Cl- are absorbed, guard cells react sensitively and can therefore have secondary effects on the entire metabolism. The accumulation of salt ions as well as the decrease in potassium, that is well known to be a side effect of Na+ accumulation, will certainly interfere with guard cells physiology because potassium is a crucial regulator for stomatal movements. Our analysis will be done on the basis of individual guard cells to increase the spatial information about the cell type-specific physiological responses. The use of the latest high-resolution methods (EDX, SIMS) enables an analysis of the ionic composition of the individual guard cells.

• DFG Programme: Research Grants