Supervisors: Dr. Hannes Kollist, Institute of Technology, University of Tartu, Estonia
Dr. Ebe Merilo, Institute of Technology, University of Tartu, Estonia
Opponent: Dr. Nathalie Leonhardt
Institute of Environmental Biology and Biotechnology. CEA Cadarache. UMR 7265 CNRS-CEA-Université Aix-Marseille II. France
Stomata are microscopic pores on the surface of leaves, mediating CO2 uptake and transpirational water loss. Stomata close when ions are released from the two guard cells surrounding each pore. Understanding the mechanisms of stomatal regulation would help to design next generation drought tolerant cultivars in crop breeding.
We studied the signaling pathways leading to stomatal opening or closure. Thale cress plants were placed into hermetically sealed flow-through chambers and the amount of water evaporating from the plant was measured. Darkness, elevated CO2, low air humidity, plant hormone abscisic acid (ABA), and ozone induce stomatal closure, resulting in decreased evaporation from the plant. Conversely, light, reduced CO2, and high humidity induce stomatal opening, which is manifested by larger amount of water transpired from plant.
We studied the ABA signaling pathway and showed that the components of ABA signaling pathway participate in stomatal closure induced by different abiotic factors. This can be illustrated with mutant plants lacking ABA receptors – these plants also lack stomatal closure in response to ozone, darkness, low air humidity and have reduced response to elevated CO2.
Stomatal opening and closure are opposite processes as regards the direction of ion movement, but are partly co-regulated. SLAC1 anion channel mutants with impaired stomatal closure were also slow in stomatal opening, even though the mutated anion channel only mediates ion efflux. We showed with our San Diego (USA) collaborators that the slow stomatal opening is caused by reduced K+ uptake due to increased Ca2+ concentration and sensitivity in guard cells of plants without functional SLAC1.
The intertwined nature of stomatal opening and closure pathways creates a challenge for both plant genetic research and genetic engineering as even single mutations can lead to changes which are not directly related with the missing protein.