Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Norman Hüner

Abstract

I assessed the effects of photosystem II excitation pressure on chloroplast biogenesis and leaf sectoring in the Arabidopsis thaliana variegated mutants im, spotty, var1, var2, chs5 and atd2. The plants were grown under varying degrees of excitation pressure induced by growth at increasing irradiance at different temperatures and the extent of variegation was quantified throughout the plant’s development. I found that the degree of variegation was positively correlated with excitation pressure, regardless of whether high light or low temperature was used to induce increased excitation pressure in all the mutants tested. This was irrespective of whether the mutation causing the variegated phenotype in the first place affected photosynthetic electron transport or not. Additional experiments examining chloroplast development in wild-type and im were performed, utilizing etiolated seedlings greening at high and low excitation pressure and they revealed a role for IM acting as an electron safety valve in photosynthetic electron transport, alleviating excitation pressure during the first 3-12 h of greening, ensuring an orderly chloroplast development. Further I analysed the effects of excitation pressure short-term stress and long-term acclimation on global gene expression in wild-type A. thaliana, in order to assess whether retrograde signalling resulting from excitation pressure causes mainly changes in photosynthesis associated transcripts, or if the plant’s response to thylakoid redox imbalance extends beyond the chloroplast. To modulate the redox state of the photosynthetic electron transport chain I used high light, low temperature and two specific inhibitors of electron transport. In order to acclimate plants to high excitation pressure they were grown at either low temperature or high irradiance. Gene expression was monitored using whole genome microarrays and it could be shown that while the stress response resulted in a drastic change in gene expression associated with photosynthethis and a large number of other metabolic pathways, the acclimation strategy to excitation pressure rather involved genes associated with gene expression and development. Even though the stress and the acclimation response function in fundamentally different ways, they temporally overlap, as ca. 30 % of all genes regulated by acclimation were already differentially expressed one hour into the stress response.


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