The response of Arabidopsis thaliana roots to mechanical impedance

In soils, plants often encounter barriers to their growth and must be able to respond to stress appropriately. Mechanical impedance has previously been shown to reduce root elongation and may have a negative impact on crop yields. It is therefore important to understand how root growth and development is regulated in response to encountering a barrier. Plant roots respond to changes in their environment through regulating the rates of cell division and the extent of cell expansion at the root tip. These developmental changes are mediated by interactions between several classes of hormones that form a complex network with key regulatory genes. The objective of the work described in this thesis is to examine the response of Arabidopsis thaliana roots to mechanical impedance and determine the hormonal signalling events involved. The work presented here uses a range of techniques to answer this question including microscopy, genetics, chemical intervention, RNA-Sequencing and analysis of published literature. Upon encountering a barrier, Arabidopsis root growth is reduced and shows a characteristic “step-like” growth pattern and it was established this response is caused by a reduction in cell elongation. RNA-Sequencing data revealed the gene transcription changes that occur in response to a barrier. Data from RNA-Sequencing and previous literature were used to generate hypotheses about the hormonal control of root growth during the barrier response. Data presented in this thesis identified a role for auxin and ethylene signalling during the barrier response. During bending, changes in the levels and distribution of auxin were observed. The role of reactive oxygen species (ROS) signalling was also investigated, providing some evidence for its involvement in root mechanical responses. Integrating evidence from RNA-Sequencing, experimental work and evidence from the literature, I have constructed a model of hypothesised pathways involved during root response to a barrier.