A photo microcalorimetric system for studies of plant tissue.

A gas perfusion microcalorimeter, primarily designed for studies of plant tissue, has been equipped with light guides in order to allow studies under the influence of light (UV-vis), and with variations in gas phase composition. The calorimetric system consists of three twin microcalorimeters of the heat conduction type positioned in a thermostated water bath. The biological sample is placed in a 20-ml photo calorimetric vessel. Light is introduced by means of a quartz rod connected to one of the arms of a bifurcated light cable. The other arm of the cable is connected to a second microcalorimeter, serving as the photo calorimetric reference. The gas flow leaving the main calorimeter will pass the reaction vessel of the third microcalorimeter, where CO2 is trapped by NaOH solution. The measurement with this calorimeter will lead to values for the rate of uptake/release of CO2 by the biological sample. Test experiments have been conducted with pieces of spinach leaf, and values have been derived for the uptake of light energy at different concentrations of CO2. From the calorespirometric results a value was derived for the Gibbs energy of formation of photosynthate from CO2 and H2O.