%0 Generic
%A Zauser, Martin
%C Heidelberg
%D 2021
%F heidok:30325
%K communication, information transfer, decoding, plant stress, analysis, modeling, image analysis
%R 10.11588/heidok.00030325
%T Communication in Plants: Analysis and Modeling of Calcium Signatures in Arabidopsis thaliana
%U https://archiv.ub.uni-heidelberg.de/volltextserver/30325/
%X Plants have a sessile lifestyle and cannot run away when attacked. They have therefore developed various defense systems to deal with potential predators or bacteria and fungi. But heat, drought or high concentrations of salt in the water also mean stress for the plant. Calcium plays an important role as a signaling molecule in the transmission of the stress stimulus within the plant. Plants of the species Arabidopsis thaliana can be genetically modified so that their calcium concentration is visible under the microscope. These plants were stimulated by my cooperation partners with various biotic and abiotic stress stimuli and recorded with the camera. As a response, the time-lapse recordings show a locally limited increase in the intracellular calcium concentration close to the root tip, which runs in waves through the plant.    The aim of my work was to analyze the wave qualitatively and quantitatively and to investigate the connection between the type of stimulus and the spatio-temporal pattern of the wave, the calcium signature. By means of modeling, I investigated how this wave can propagate at high speed across cell boundaries and how different responses to a calcium signal can be triggered at the protein level. The course of the calcium wave can be displayed as a kymograph, a space-time diagram. Using the kymograph, I managed to quantify the wave and to determine characteristic parameters such as start time, start position, and speed. The image series of the individual experiments show a high variance with respect to intensity and shape of the calcium wave. To the purpose of convenient evaluation, I designed an analysis script that quantifies the calcium wave automatically. Firstly, the root is detected in an image series. Secondly, a kymograph is created from the mean calcium concentration along the root. Finally, the calcium wave is plotted as a thin, sharply outlined line. This so-called crestline plot highlights the characteristic properties of the individual wave and allows an easy approximation of aforementioned wave parameters. The analysis of the experiments revealed that stimulation with salt leads to an immediate, short-term increase in the calcium concentration, while bacteria or fungi trigger a delayed calcium wave that propagates at a speed of a few µm/s.    It is known from the literature that after stimulation of the root with elevated levels of salt, the wave moves through the plant at a high speed of around 400 µm/s. A combined signal transmission of intracellular calcium and extracellular reactive oxygen species (ROS) is suggested as a possible explanation. Together with my cooperation partner, I designed a corresponding mathematical model and adapted it to the different cell sizes in the root tip. We were able to show that wave propagation based only on intracellular calcium is sufficient for the much slower calcium wave after stimulation with bacteria or fungi. However, the calcium wave after stimulation with salt requires additional components. Based on a simulation, I was able to demonstrate that the plasmodesmata, the narrow tubes between adjacent cells, slow down the expansion of the wave considerably and should not be ignored.    The plant can use calcium-dependent protein kinases (CPKs) to decode the calcium signal and translate it into protein phosphorylations as a starting point for further reactions. For example, the closing process of the stomata is based on the calcium-regulated activation of CPKs. Based on experimental data, I developed a CPK protein model for different CPKs. In a computer simulation, I coupled calcium time series from a stimulation experiment of guard cells and epidermal cells to my protein model and examined the activity of the CPK proteins. I was able to show that by varying the calcium signal, different CPK proteins can be addressed and the stress response of the plant can be adapted to the type of stimulation.