Capillary Organic Electronic Ion Pump for Delivering Malic Acid - Towards Better Understanding of Drought Tolerance in Tropical Plants

Sammanfattning: Delivery of biologically relevant ions such as drugs, neurotransmitters and hormones have been recognized as powerful a tool to control physiology of animals and plants for research purposes and practical applications. In the plant research community, ions are most commonly delivered as part of a solvent by soaking, spraying, pipetting or by adding to the soil. These methods have low control of the delivery dynamics and quantity of ion uptake. These issues motivated the development of the Organic Electronic Ion Pump (OEIP), which delivers only ions of interest by applying an external electric field through a polyelectrolyte membrane of high fixed charge concentration. A miniaturized, implantable version of the OEIP based on capillary fibres (c-OEIP), where the polyelectrolyte is enclosed in a capillary, enabled even higher precision of the delivery. In this master thesis, c-OEIP has been applied in the tropical plant Kalanchoe Blossfeldiana, chosen due to its characteristic skill to gradually learn to save water: while maturing it shifts to night time photosynthesis and transpiration, called Constitutive Crassulacean Acid Metabolism. A better understanding of this metabolism and water saving ability could guide engineering of enhanced drought tolerance in crop plants, which is motivated by the increasing global warming. One of the biologically relevant ions that is potentially involved in this water-saving learning process is the malate ions. The aim of this thesis is to test the hypothesis that c-OEIP is able to deliver malate ions to cause a reduction in stomatal conductance and transpiration of intact leaves of Kalanchoe Blossfeldiana. To test this hypothesis, firstly, the capillary-based OEIP were fabricated using polyimide coated glass capillaries filled with AETMAC polyelectrolyte. The ability of these devices to deliver malic acid (MA) was verified by using current-voltage characterisation during loading and delivery of MA. Secondly, the setup for MA delivery with c-OEIP to intact kalanchoe leaf was developed, optimising the insertion method to minimize the wounding of the plant and increase assay reproducibility. Finally, the MA was delivered to intact kalanchoe leaves via c-OEIP, where the plant transpiration response was evaluated using standard gas exchange porometer and also novel infrared camera, as plant temperature can be correlated with plant transpiration status. The results indicate that c-OEIP can deliver MA and trigger reduction of transpiration of young kalanchoe leaves, supporting the hypothesis that malate ions act to reduce stomatal conductance, potentially conveying a feedback message from the mesophyll to the guard cells.