Influence of nitrate availability and environmental stimuli on seed germination and stomatal behaviour

An expanding global population is putting pressure on the world’s climate and global food supply chain, with governments simultaneously restricting the use of nitrogen fertilisers. The implications for food security has never been more urgent. Plants need to adapt to rapidly changing environments and understanding how plants respond including levels of nitrogen and abiotic stresses is critical.
This thesis aimed to identify the effects of reduced nitrate assimilation on plants’ health and growth, by utilising mutants deficient in nitrate reductase and observing their responses to abiotic stresses. Initial investigations suggested gene redundancy for the nitrate reductases NIA1 and NIA2, indicating their involvement in different stress responses. Regulation of their transcription factors also appears to play a role in plant health and growth.
Secondly, how nitrate availability affects responses to abiotic stresses was explored. This was achieved by utilising dynamic thermal imaging, salt and a range of nitrate reductase and stomatal mutants. Studies showed that ABA induced stomatal closure is influenced by endogenous nitrate and remains unaffected by exogenous nitrate application.
Thirdly, identify novel stomatal regulators, focusing on post-transcriptional modifications, specifically kinases and phosphatases was explored. A literature review was undertaken to identify potential candidates; 10 were chosen for further study. Phenotypic analysis was undertaken on two of the identified candidates, using a range of techniques. The study showed that, potential stomatal regulators PSKR2 and GCK1 were identified, but further analysis is required.
Overall, whilst initial data indicate the existence of complex interactions between multiple pathways, signalling and developmental, determining the exact causes requires further investigation. This research enhances understanding of plant responses to environmental stresses, has developed and presented novel methods to study stress responses in whole crop plants, and provides new knowledge that can be used to enhance crop resilience and help ensure global food security.