SP03: ABA dynamics in angiosperm leaves control long-distance water transport via stomata

• Applicant: Professor Dr. Steven Jansen
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538902328

How plants respond to environmental changes within a soil-plant-atmosphere continuum is of fundamental importance for their growth resilience, especially under drought. Within the SOPHY research unit, this project investigates the role of abscisic acid (ABA) dynamics in leaves in regulating stomatal closure to ensure that drought-stressed angiosperms remain within a zone of hydraulic linearity (i.e., the relationship between transpiration and leaf water potential is linear). We explore two hypotheses: (1) stomata close proactively in response to changes in leaf water status, mediated by ABA biosynthesis and catabolism, avoiding the onset of hydraulic non-linearity, and (2) the hydraulic resistance from root xylem to stomata affects ABA dynamics in such a way that plants under drought maintain hydraulic linearity. Testing these hypotheses will link physiological, biochemical, and anatomical traits with hydraulic resistance from the root xylem to the sites of transpiration near the stomata. To enhance collaboration and complementarity within SOPHY, we will study the same four angiosperm species as other subprojects: two annual herbs (Zea mays, Helianthus annuus), and two woody trees (Tilia cordata, Fagus sylvatica), both under conditions of controlled soil drought and vapour pressure deficit, and under field conditions. We will quantify ABA levels, catabolites, stomatal conductance, and leaf water potential in ABA-deficient mutants of the herbs, and wild-type lines of all species. Hydraulic resistance will be determined anatomically along the xylem pathway using vessel length measurements, conduit diameter analysis, and modelling of lumen and end-wall resistances, while outside-xylem resistance will be measured experimentally and further complemented with data on apoplastic and symplastic barriers. A key innovation lies in integrating hydraulic traits with ABA analyses to identify whether ABA dynamics are driven by changes in hydraulic resistance along the hydraulic pathway. We expect that outside-xylem resistance and mesophyll dehydration are critical triggers of ABA production. Furthermore, anatomical characters will be related to stomatal sensitivity and ABA dynamics under drought, while PhylloClip sensors will be applied to monitor transpiration continuously and to measure the hydroscape area. By comparing sun- and shade-developed leaves, we will also assess how leaf anatomy influences the thresholds for stomatal regulation. By bridging hormone signaling, plant anatomy, and ecophysiology to better understand how angiosperms control transpiration and prevent drought-induced damage, this subproject has strong interactions with all other subprojects within SOPHY. Results will feed into the SOPHY core model, which aims to integrate physiological processes, mechanisms, and traits underlying the ability of plants to avoid hydraulic nonlinearity.

• DFG Programme: Research Units
• Subproject of: FOR 5820: Soil-plant hydraulics impacting transpiration and plant growth in response to drought [SOPHY]
• International Connection: USA
• Cooperation Partner: Professor Scott A.M. McAdam, Ph.D.