Stomata are pores found on the epidermis of most aerial parts of plants and are formed by a specialized pair of cells, the guard cells. Stomata enable the uptake of CO2 in expense of water vapour release and therefore optimize the trade-off between transpirational water loss and carbon gain. Regulation of gas exchange is achieved by controlling the stomatal pore aperture involving the osmotic solute accumulation. Fluxes of K+ are mediated by the plasma membrane inward and outward rectifying K+ channels (KIN and KOUT), while the anion channels enable Cl- fluxes. Stomata in most plants follow the �one cell spacing rule� implying that the separation of stomata by at least one epidermal cell. However, there are several genera exhibiting stomata clusters, such as the genus Begonia. In this study I have used two Begonia species as well as Arabidopsis stomatal patterning mutants to explore the impact of stomatal clustering in plant physiology. In the tmm1 mutants the stomatal movements suppressed gas exchange responses when plants were exposed to light and darkness. Kinetic analysis of the K+ channels uncovered changes in the gating characteristics that affected the activity of KOUT channels as well as the voltage-dependence of KIN channel opening. Tail current analysis of K+ channels demonstrated that the effect was to reduce accumulation of K+ ions in the cytosol of guard cells from tmm1 plants. Raising light intensity and lowering evaporative demand enhanced WUE and growth of plants exhibiting single stomata, albeit the tmm1 mutant plants failed to respond likewise. Astonishingly, the tmm1 mutants were more resilient to prolonged drought stress via minimizing the transpirational water loss. Phenotypic analysis also revealed that the impaired stomatal behaviour of the tmm1 plants attenuated root growth under sucrose abundant conditions. I have also made use of the novel gasotransmitter hydrogen sulfide (H2S) to examine its effect on stomata. H2S-induced stomatal closure in both Arabidopsis and tobacco plants was dependent on the exclusive inhibition of KIN channels. The data implied a partial sensitivity of H2S effect to the intracellular Ca2+ levels, and modelling also suggest a role for pH in the H2S-mediate response. The tmm1 mutants did not respond to H2S in a wild type fashion, indicating that stomatal movements are altered irrespectively to the nature of stimuli. Collectively, my data suggest that stomatal spacing and their associations with neighbouring epidermal cells is important for the K+ relations of guard cells and their capacity to drive stomatal movements. The role of spacing was crucial for gaseous exchange as well as plant growth under favourable conditions. The data also provided novel insights into the network governing stomatal behaviour and positioned H2S to an independent branch of the ABA pathway. Finally, the data suggested an adaptive role for stomatal clustering under water-limited habitats and a potential use of H2S as a tool to minimize transpirational water loss.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:656253 |
| Date | January 2014 |
| Creators | Papanatsiou, Maria |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/6514/ |
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