F. Harren

Sensitive intracavity photoacoustic measurements with a CO2 waveguide laser

A photoacoustic intracavity configuration is presented; a resonant photoacoustic cell excited in its first longitudinal mode is placed inside the cavity of a CO2 waveguide laser. Due to the high laser power and the sharp intracavity focus, saturation effects occur in the excitation and relaxation process of absorbing C2H4 molecules. A more optimal configuration is applied to measure the C2H4 emission of several Rumex species. A detection sensitivity of 6 ppt (parts per trillion) C2H4 is reached, equivalent to a minimal detectable absorption of 1.8×10−10 cm−1.

The role of ethylene in shoot elongation with respect to survival and seed output of flooded Rumex maritimus L. plants

Rumex maritimus L. occurs in frequently flooded sites of lowland flood plains. Upon submergence this species exhibited rapid elongation of shoots, but the response depended upon the developmental stage when flooding was initiated. In the rosette stage, petioles showed a fast and large response; during early stem elongation the response of petioles was less, but the extension of the lower internodes considerable; during flowering stem development, high internodes extended and the contribution to final stem length diminished. Ethylene production by an intact plant before, during and after submergence was measured with a laser-driven photoacoustic technique. Internal ethylene concentrations increased within 12 h of submergence. Ethylene accumulated in the submerged plant due to increased synthesis as well as a reduced diffusion from the plant to the water (instead of air). The elongation response could in part be mimicked by exogenous ethylene. Directly after submergence a further increase of ethylene synthesis was observed, which may be of vital importance in causing shoots to continue their rapid elongation even after the water surface is reached. The responses of shoots were related to fitness in experimental field plots. Survival of submerged R. maritimus depended on its ability to emerge above the water surface, while seed production was positively correlated with shoot height above the

Trace Detection in Agriculture and Biology

The use of the photoacoustic effect for new applications in agricultural biology is the subject of this chapter. Section 8.1 deals with the photoacoustic detection of ethylene that is produced by specific plant species during senescence and inundation. It was jointly written by the groups of Molecular and Laser Physics (F. Harren, J. Reuss, F. Bijnen) and Experimental Botany (L. Voesenek, C. Blom) from the Catholic University, Nijmegen, and E. Woltering, associated with the Sprenger Institute in Wageningen.

Ethylene Exhalation of a Single Flower Detected by Photoacoustic Methods

The combination of a powerful CO2 waveguide laser and a resonant photoacoustic cell provides sufficient sensitivity to investigate the emission of ethylene from a single orchid flower (Cymbidium Mary Pinchess “Del Rey”) in the interval up to 70 hours after emasculation of the flower. Ethylene plays a special role in agriculture. As an air pollutant it inhibits the growth of plants, causes yellowing and abscission of leaves and wilting of flowers /1/. As a gaseous hormone produced by the plant itself, it causes the same effect in unpolluted plants under closed storage.

Sensitive Photoacoustic Trace Detection of Ethylene

Tunable diode lasers have been combined with photoacoustic detection; the envisaged minimum detection limit is 20 ppb. Employing an intracavity CO2-laser set up, photoacoustic detection leads to a more than thousandfold improvement of sensitivity for C2H4. This very sensitive scheme is applied to observe the production of stress-ethylene of single plants (Rumex palustris) as response to partial inundation.

Early Changes in Ethylene Production during Senescence of Carnation and Phalaenopsis Flowers Measured by Laser Photoacoustic Detection

A CO2 laser-based photoacoustic method was used to determine the early changes in ethylene production during senescence of carnation (Dianthus caryophyllus) and emasculated orchid (Phalaenopsis) flowers. Individual flowers were placed in small cuvettes (80 ml) and flushed with purified air (flow rate 0.9 1/h). The effluent was directed through a photoacoustic cell for determination of ethylene. The laser photoacoustic equipment consisted of a line tunable CO2 laser in conjunction with a single-pass resonant acoustic cell. The minimum detection limit of the system for ethylene was 0.03 nl/1.