QUANTITATIVE IMAGING OF CHLOROPHYLL FLUORESCENCE

A computer-controlled video system is described where images of chlorophyll fluorescence from oat (Avena sativa L.) leaves are captured throughout an induction curve. The fluorescence parameters Phi(II) and Delta F-m /F-m', which represent photosystem II photochemical efficiency and non-photochemical quenching respectively are calculated from images taken under actinic and saturating illumination. They are compared with the equivalent parameters determined from simultaneous measurements made with a non-imaging modulated fluorimeter. The leaves are imaged in the chamber of an infra-red gas analyser, allowing the relationship between the fluorescence parameters and CO2 assimilation to be determined. Under a series of illumination conditions and partial pressures of CO2 the values of Phi(II) determined by image analysis are in close agreement with those obtained by modulated fluorimetry and are linearly related to CO2 assimilation. The values of Delta F-m/F-m', determined by image analysis are linearly related to those obtained by modulated fluorimetry but the absolute values differ between the two systems. The video system described can be used to examine quantitative changes in fluorescence parameters in a heterogeneous system.