QUANTITATIVE IMAGING OF CHLOROPHYLL FLUORESCENCE

A computer-controlled video system is described where images of chloro phyll fluorescence from oat (Avena sativa L.) leaves are captured thro ughout an induction curve. The fluorescence parameters Phi(II) and Del ta F-m /F-m', which represent photosystem II photochemical efficiency and non-photochemical quenching respectively are calculated from image s taken under actinic and saturating illumination. They are compared w ith the equivalent parameters determined from simultaneous measurement s made with a non-imaging modulated fluorimeter. The leaves are imaged in the chamber of an infra-red gas analyser, allowing the relationshi p between the fluorescence parameters and CO2 assimilation to be deter mined. Under a series of illumination conditions and partial pressures of CO2 the values of Phi(II) determined by image analysis are in clos e agreement with those obtained by modulated fluorimetry and are linea rly related to CO2 assimilation. The values of Delta F-m/F-m', determi ned by image analysis are linearly related to those obtained by modula ted fluorimetry but the absolute values differ between the two systems . The video system described can be used to examine quantitative chang es in fluorescence parameters in a heterogeneous system.