Oxidative stress and pathogenic attack in plants, studied by laser based photoacoustic trace gas detection

摘要

Photoacoustic detection has proven to be a sensitive method, which is suitable for trace gas measurement. In this thesis, we improved the photoacoustic detection system to measure new biologically interesting gases, ethane (C2H6) and nitric oxide (NO). A new design of grating holder is incorporated into the CO laser that provides the possibility to operate the laser in two different wavelength regions, the fundamental and the first overtone vibrational transition, working at 4.6 - 8.2 micrometer and 2.62 - 4.06 micrometer, respectively. High laser power could be obtained in the fundamental mode, more than 30 Watt intracavity on the strongest lines. In this region different gases show strong absorption, e.g. ethanol, acetaldehyde and also nitric oxide. Operation of the CO laser in the first overtone mode yields about 11 Watt intracavity on the strongest lines. Ethane, ethylene and pentane show strong absorption in this first overtone wavelength region. The possibility of running the laser in two different modes opens wider application; nitric oxide was measured using the fundamental mode and ethane employing the first overtone mode. Ethane and nitric oxide were measured from plants under various kinds of stress. It is well understood in literature that in many cases stress causes the formation of reactive oxygen species that can initiate lipid peroxidation. This process yields ethane as one of the final products. Applying photoacoustic detection we were able to measure ethane and thus follow directly the response of plants to abiotic stresses such as chilling under light, submergence and artificial aging. Recently, it has been reported that nitric oxide is involved in the defense mechanism of plants against a pathogen invasion. We measured in real time nitric oxide released by tobacco leaves under pathogenic attack