Abstract
dc:description.abstractRegulation of the stomatal response to red light Stomata are microscopic pores in the leaf epidermis which govern the exchange of CO2 and water vapour between the plant and surrounding atmosphere. Highly specialised guard cells surround each stomatal pore and regulate stomatal aperture in response to various environmental and endogenous cues. The mechanisms underlying the ‘quantitative’ red light response of stomata, which links stomatal conductance with CO2 assimilation rates in the underlying mesophyll, remains elusive. Initially, it was suggested that changes in intercellular CO2 (Ci) provide the main cue. However, evidence for C¬i-independent red light responses suggest an additional, more direct relationship with photosynthesis. One current hypothesis is that the redox state of the chloroplast plastoquinone (PQ) pool could coordinate the Ci-independent response to red light. However, the exact site of perception, and the mechanisms and cell types through which the red light stimulus is communicated remain unknown. This thesis will address some of the major questions surrounding the elusive red light response. The first experimental chapter aimed to quantify the relative contribution and characterise the interplay between Ci-dependent and -independent components of the stomatal response to red light. Measurement of stomatal red light response curves at a range of constant Ci values for wild-type Arabidopsis (Col-0) and the CO2 hyposensitive mutant, ca1ca4, enabled separation of the Ci-dependent and -independent red light responses. Surprisingly, both were found contribute equally to the overall red light response, but Ci-independent opening was found to be suppressed at high Ci. In addition, concurrent chlorophyll fluorescence measurements confirmed previously observed relationships between PQ redox state and stomatal conductance, consistent with the putative involvement of PQ redox state in coordinating the Ci-independent response. Subsequently, the second experimental chapter aimed to identify the signalling mechanisms which coordinate the Ci-independent red light response pathway. Specifically, the hypothesis that hydrogen peroxide (H2O2) connects PQ redox with stomatal aperture changes was tested by investigating coordination between PQ redox state, cytosolic H2O2 accumulation and stomatal opening in mutants with altered levels of Photosystem II subunit S (PsbS) in the Arabidopsis Col-0 genetic background, as well as in the ascorbate peroxidase1 (apx1) H2O2 scavenging mutant. Notably, alterations in stomatal red light responses corresponded with altered guard cell H2O2 accumulation and could be explained by parabolic responses of stomatal movements to H2O2. Finally, the last experimental chapter investigated the cellular specificity of H2O2 signals in the Ci-independent response to red light. At the start of this work, it was entirely unclear whether the Ci-independent red light response originated within the guard cells or the underlying mesophyll, or both, with limited and contrasting evidence from previously published work. To explore this further, APX1 was complemented into the apx1 genetic background in a cell-specific manner, using either guard cell- or mesophyll-specific or ubiquitous promoters. The effect of these manipulations on guard cell H2O2 accumulation, red light stomatal opening responses and H2O2 dose response curves demonstrated that H2O2-dependent stomatal movements are predominately coordinated by guard cell cytosolic H2O2 levels, but that mesophyll photosynthetic H2O2 production also affects guard cell H2O2 levels, and as such stomatal opening, albeit to a lesser degree. Overall, this thesis demonstrates that H2O2 acts as a key signalling molecule in the Ci-independent stomatal response to red light, linking photosynthesis to stomatal movements, with potential implications for improving plant water-use efficiency.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2024
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Taylor, Georgia
- Advisor dc:contributor.advisor
-
- Kromdijk, Johannes
Subjects
dc:subject × 9Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.116009
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/380358