Laser-driven photoacoustic spectroscopy: what we can do with it in flooding research

Photoacoustic spectroscopy is a highly sensitive technique for measuring low molecular weight gases such as the plant hormone ethylene. Due to its high sensitivity (10 p11–1 ethylene), photoacoustic spectroscopy can be combined with flow-through systems that avoid the need for enclosing excised plant parts in small volumes for head-space analysis. In this way, artifacts introduced by various accumulation techniques can be avoided and ethylene production monitored at short intervals in air or other gas mixtures as it flows out of a cuvette enclosing all or part of an intact plant. The principles of this technique are described. Three case studies demonstrate the application of photoacoustic spectroscopy in flooding research. These studies concentrate on accurate measurement of endogenous ethylene concentrations in submerged shoots and roots, root ethylene production under subambient oxygen pressures and the simultaneous measurement of ethylene production and leaf growth. In addition, the qualitative and quantitive methods previously used to measure the gaseous plant hormone ethylene are briefly reviewed. Finally, the future prospects of photoacoustic spectroscopy in flooding research are discussed.