Browsing by Subject "valostressi"

Fluctuating light conditions can cause light stress for plants. The photosynthetic apparatus can be damaged by the excess light. Light stress causes formation of reactive oxygen species in chloroplasts. Arabidopsis thaliana’s mutant radical induced cell death1 (rcd1) is tolerant to this stress. In my thesis I used a compound called methyl viologen which causes the formation of reactive oxygen species in chloroplasts. It has been used as a herbicide. By using this compound, we can make the light stress worse and see bigger differences between the rcd1 mutant and the wild type. We identified the causative gene of rcd1’s chloroplastic stress tolerance, clarified the dependence of growth light intensity for chloroplastic stress tolerance and explored possible structural differences at the cellular level between the wild type and rcd1. Finding the genes that prevent light stress would allow a light stress tolerant crop production which could make food production easier in hot and dry areas of the world. My thesis is a part of a screening study where rcd1 mutants were screened for lowered tolerance to light stress. The amount of stress of the leaves was defined by measuring the chlorophyll fluorescence. Two most promising lines which got damaged by methyl viologen were called #20 and #54. For these a backcrossing was made with the rcd1. Clear correlation was found from their offspring between the phenotype and the methyl viologen tolerance. The correlation was strongest in the line #20 so we focused on it. Small and yellowish pale individuals which resembled their parents were the most sensitive to methyl viologen. These individuals were selected for the sequencing. Candidate genes were in the chromosome 3. The most promising one was called AT3G29185 or BIOGENESIS FACTOR REQUIRED FOR ATP SYNTHASE1 (BFA1). We ordered bfa1 mutant’s seeds. We found that bfa1 mutant was itself sensitive to methyl viologen proving our observation. We discovered that methyl viologen tolerance is growth light dependent. The individuals that grew under higher intensity of light were more tolerant to methyl viologen in both the wild type and rcd1 mutant. We didn’t find structural differences at the cellular level by confocal microscopy. Thus, they can’t explain the differences in the methyl viologen tolerance.