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Mills, Hayley (2021) Plant calcium dynamics: signalling the way to sustainable food production. PhD thesis, University of Nottingham.

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Abstract

In this work we explore the calcium signalling pathway mediating symbiotic associations between legumes and Nitrogen-fixing bacteria. This symbiotic process has been identified as a possible 'biological' alternative to using environmentally damaging synthetic fertilisers in crop production. Therefore, motivated by the challenge of ensuring worldwide food security whilst utilising increasingly degraded soils, we look to advance the knowledge of the signalling pathway that facilitates nodulation in order to progress towards the transfer of this favourable trait from legumes to cereal crops.

A mathematical model representing the flux and diffusion of calcium in the plant cell nucleus was derived for up to 3-dimensions in both spherical and prolate spheroidal coordinates. Our final model is the first 3-dimensional representation of nuclear plant calcium signalling. It is also the first to reproduce the exact spiking dynamics reported in the literature, without the need for any additional inputs such as refractory periods or buffers. In a novel and exciting finding, we show that nuclear calcium oscillations can be generated autonomously provided that the channels which facilitate them form clusters. The resulting calcium signatures are presented for clustered and distributed channels and we examine the microdomains over which these patterns occur. It is also found that the formation of these microdomains is necessary for calcium concentrations to exceed the binding threshold of downstream sensory protein CCaMK. This provides new insight into the possible mechanism of generation of the nuclear calcium signature, suggesting a potential multi-functional role for cluster formation.

The mathematical method through which this was achieved involved solving the heat equation semi-analytically in order to obtain a series of Green's functions. This provides us with a useful 3-dimensional framework which allows us to perform simulations significantly faster than could be achieved through traditional finite-element methods.

An experimental methodology, using plant lines expressing GCAMP suspended in a FlowCell device, was developed in order to successfully image calcium signalling over longer times, with easier stimulus application. This was used to compare the calcium response in \textit{Arabidopsis thaliana}, hereby Arabidopsis, with \textit{Nicotiana benthamiana} highlighting the difference in calcium signalling between species with and without nodulation abilities. Original data on the geometry of the nucleus was collected for parameterisation of our model. Analysis of this data revealed statistically significant differences in nuclear morphology between cortical and root hair cells and also revealed a correlation between the nuclear morphology of cells in the elongation zone and their distance from the root apex.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Thul, Ruediger Coombes, Stephen Wells, Darren
Keywords:	calcium signalling pathway, nitrogen fixing, mathematical modelling
Subjects:	Q Science > QA Mathematics > QA299 Analysis S Agriculture > S Agriculture (General)
Faculties/Schools:	UK Campuses > Faculty of Science > School of Mathematical Sciences
Item ID:	66216
Depositing User:	Mills, Hayley
Date Deposited:	31 Dec 2021 04:40
Last Modified:	31 Dec 2021 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/66216

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