Plant growth and survival is fundamentally linked with the ability to detect and respond to abiotic and biotic factors. Drought and osmotic stress are two key environmental factors accelerated by climate change. Both stresses directly and indirectly affect plants’ immunity and development with severe impact on agriculture and ecosystems. Although the connection between drought, osmotic stress and immunity have a detrimental impact on plants, our knowledge on the associated sensing mechanisms, reciprocal interactions and combinatory effects on plant health is very limited.

Cytosolic free calcium (Ca2+) is a key secondary messenger in signal transduction pathways associated with mechanical, osmotic stress and the plants’ innate immune system. These stresses trigger an increase in root cytosolic free Ca2+ initiating production of the reactive oxygen species (ROS), like hydrogen peroxide (H2O2). Both signal transduction pathways might contribute to abiotic stress adaptation and plant defence. Ultimately, cross-talk between pathways relying on Ca2+ signalling is unavoidable. Consequently, this research will analyse root-specific expression of the calcium binding protein calmodulin (CaM) and calmodulin like proteins (CMLs), to further elucidate the impact of abiotic and biotic stress on Ca2+ signal regulation for plant defence.

Arabidopsis thaliana plants containing a fluorescent Ca2+-detector were utilised to visualise Ca2+ signals in the primary root of 7-day old plants. An agarose based channel and pre-published dual- flow-RootChip (dfRC) with unidirectional flow were fabricated to visualize the signal induced by different osmotic stressors in the root. To further elucidate the bidirectionality of Ca2+ signals in plant roots, an optimised root chip was designed for the selective application of abiotic stressors at the root tip and root maturation zone (bi-dfRC). Observations made during this project confirmed the hypothesis that the plant roots perception of osmotic and drought stress is linked to different spatiotemporal patterns of Ca2+ signals. This research hypothesises that the variations in Ca2+ signals are associated with the fine-tuning process associated with the adaptation of the plants to the constantly changing environment. Root chip microfluidic technology will provide a novel approach to challenge plant roots with two different conditions simultaneously, observe high- resolution signal transduction and local adaptation to drought and osmotic stress.