Quantitative imaging of chlorophyll fluorescence

A computer-controlled video system is described where images of chlorophyll fluorescence from oat (Arena saliva L.) leaves are captured throughout an induction curve. The fluorescence parameters φ₁₁ and ΔF_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 φ₁₁ determined by image analysis are in close agreement with those obtained by modulated fiuorimetry and are linearly related to CO₂ assimilation. The values of ΔF_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.