| Summary: | 碩士 === 國立高雄大學 === 生命科學系碩士班 === 107 === In recent years, the phenomenon of the ozone depletion has become more and more serious, which has weakened the ability of the stratosphere to absorb solar radiation, indirectly leading to global warming. Previous studies mentioned enhanced ultraviolet light (UV) destroys the photosynthetic organs of plants, causing disturbance and inhibition of photosynthetic capacity. Previous studies also pointed out that some crops lead to early flowering and reduced yield under high temperature environment. Therefore, this study investigated the effects of UV and heat stress on foxtail millet (Setaria italica), which has strong adaptability, good tolerance to abiotic stresses, rich diversity and small genome. One-month old foxtail millet was irradiated with UV radiation and 39℃ heat treatment. The leaves of plants were severely curled after UV treatment, and the growth of plants were inhibited after heat treatment. To understand the effects of osmotic stress caused by UV and heat treatment on foxtail millet, the leaf relative water content (RWC), proline content and soluble sugar content were determined. These results showed that after UV and heat treatment, compared with the control plants, RWC decreased significantly by 3.74% and 21.77%, respectively. The proline content increased by 0.54 and 1.64-fold, respectively. The soluble sugar content increased significantly by 96.05% and 76.49%, respectively. To prove the effects of UV and heat treatment on photosynthesis efficiency of foxtail millet, chlorophyll content and fluorescence were analyzed. These results indicated that after UV and heat treatment, compared with the control plants, the chlorophyll content reduced significantly by 10.82% and 10.54%, respectively. The electron transport rate (ETR) declined significantly by 45.94% and 38.39%, respectively, at 1258 µmol m-2s-1 photosynthetically active radiation (PAR). To confirm the damage of the foxtail millet after UV and heat treatment, the concentration of reactive oxygen species (ROS) was detected. These results revealed after UV and heat treatment, the levels of H2O2 increased significantly by 73.42% and 81.61%, respectively, compared with the control plants. The transcriptional and protein activities of antioxidant enzymes were measured. We found the transcriptional and protein activities of antioxidant enzymes increased after UV treatment. However, the protein activities of antioxidant enzymes decreased significantly, but the transcriptional activities of antioxidant enzymes increased after heat treatment. In summary, this study points out under UV and heat stress, the chloroplast of the foxtail millet is damaged, resulting in decreased chlorophyll content, decreased electron transport rate, and inhibited the efficiency of photosynthesis. The damage causes by UV and heat stress also increases the production of ROS, which regulates the transcriptional and protein activities of antioxidant enzymes to resist the negative influence.
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