| Popis: |
Plants are exposed to a variety of abiotic stresses, including salinity and drought. These environmental stresses cause major losses in crop yield. High salinity stress alone impairs crop production on at least 20% of irrigated land worldwide. Thus, the development of stress-tolerant crops is of major importance for food security. Many physiological responses to ensure acclimation to adverse environmental conditions require the synthesis and perception of the plant hormone abscisic acid (ABA). Recent studies have shown that the function of the circadian clock is altered under some abiotic stress conditions such as drought, and osmotic stress. The first part of this thesis investigates the role of the stress response hormone abscisic acid in changing the function of the clock under osmotic stress. It was found that multiple core clock genes are responsive to ABA application, with sharp transient induction of morning associated genes in particular. In comparison, osmotic stress caused a damping of the amplitude of gene expression. It was then shown that the disruptive effect of osmotic stress on circadian leaf movement rhythms required the biosynthesis of ABA. This is important as it demonstrates that ABA is a key factor in mediating osmotic stress responses to the clock. The second half of this thesis then focuses on how altered function of the clock might impact plant performance under drought or osmotic stress. It was found that the morning associated LATE ELONGATED HYPOCOTYL (LHY) transcription factor, which functions as a key component of the circadian clock, regulates many of the components of the ABA signalling pathway. Evidence was provided that, while overexpression of LHY results in reduced ABA levels, ABA responsive gene expression is significantly increased upon ABA treatment. Finally, through phenotypic analysis it was determined that increased LHY expression leads to increased performance in drought and osmotic stress conditions. This is important as it suggests that manipulation of circadian clock function may be useful as a novel approach in the future engineering of stress tolerant crop lines. |
