A photoacoustic spectrometer for measuring heat dissipation and oxygen quantum yield at the microscopic level within leaf tissues

A photoacoustic instrument has been developed to measure photothermal signals and oxygen evolution at the microscopic level within leaves and leaf cross sections. The device utilizes lines of light, obtained from laser diodes, that are focussed on the sample and permit measurements with a spatial resolution of 40 mu m In cross sections of spinach leaves (700 mu m thick) the profile for the photothermal signals is bell shaped and coincides closely with the chlorophyll content of the tissues. By contrast, the profile for oxygen evolution is relatively flat, suggesting uniform capacity for oxygen evolution in the mesophyll. Maximum values for relative quantum yield for oxygen evolution are found in palisade tissues near the adaxial leaf surface. The photoacoustic device shows that it is possible to collect thermal and oxygen signals from microscopic leaf samples and opens a new avenue for studies of leaf structure-function. (C) 1999 Elsevier Science S.A. All rights reserved.