Format: ORAL

Giovanni Bortolami1, Kathy Steppe2, Jan Van den Bulcke3,4, Salma Balazadeh5,6, Iris Frederiks1, Toon Gheyle3,4, Pierre Kibleur3,4, Max Larter1,7, Liselotte de Ligne3,4, Ajaree Thonglim1, Seppe Top2, Joris Van Acker3,4, Rune Vanbeylen2, Brechtje van Helden1, Frederic Lens1,6

1Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, The Netherlands. 2Laboratory of Plant Ecology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium 3UGent-Woodlab, Department of Environment, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium. 4UGent Centre for X-ray Tomography (UGCT), Ghent University, Ghent, Belgium. 5Max-Planck-Institute of Molecular Plant Physiology (MPIMP), D-14476 Potsdam, Germany. 6Institute of Biology Leiden (IBL), Leiden University, 2333 BE Leiden, The Netherlands. 7University of Bordeaux, INRAE, BIOGECO, F-33615 Pessac, France.

Inside plants, water moves from the roots up to the leaves due to a gradient in negative pressure (i.e., tension) generated in the leaf mesophyll cells via transpiration. During intense drought periods, the tension in the xylem sap increases, leading to gas bubbles (embolisms) inside the water-conducting cells (i.e., xylem vessels), thereby obstructing the long-distance water flow. Tomato plants are known to also move water through a positive pressure generated in the roots. We hypothesize that root pressure could help tomato plants remove gas embolism after release from drought after re-watering. Therefore, we used a gantry-based X-ray microCT imaging system, the EMCT scanner at the UGCT (UGent Center for X-ray Tomography, www.ugct.ugent.be), to visualize plant re-hydration and possible embolism repair by scanning the plants before and after drought, and at different times after re-watering. In total, we followed 25 control well-watered plants and 36 drought-stressed plants (covering a wide range of drought intensities). Our results show that all well-watered plants generated root pressure and partially repaired the few embolized vessels overnight. The role of root pressure in plants subjected to drought is more ambiguous: embolism repair after re-watering was also observed, but only in the drought-stressed plants that developed root pressure after re-watering (30%), while no root pressure was detected in 70% of the drought-stressed plants after re-watering. These results show that root pressure development is not an efficient mechanism of tomato plants recovery from drought, but shows the ability of this embolism-vulnerable species to remove the first embolism events generated during the day at well-watered conditions. In conclusion, we show that root pressure in tomatoes can remove the limited daily embolism under well-watered conditions and only occasionally after drought.