MEASUREMENT OF CHLOROPHYLL FLUORESCENCE WITHIN LEAVES USING A MODIFIED PAM FLUOROMETER WITH A FIBEROPTIC MICROPROBE

By using a fiber-optic microprobe in combination with a modified PAM F luorometer, chlorophyll fluorescence yield was measured within leaves with spatial resolution of approximately 20 mu m. The new system emplo ys a miniature photomultiplier for detection of the pulse-modulated fl uorescence signal received by the 20 mu m fiber tip. The obtained sign al/noise ratio qualifies for recordings of fluorescence induction kine tics (Kautsky effect), fluorescence quenching by the saturation pulse method and determination of quantum yield of energy conversion at Phot osystem II at different sites within a leaf. Examples of the system pe rformance and of practical applications are given. It is demonstrated that the fluorescence rise kinetics are distinctly faster when chlorop lasts within the spongy mesophyll are illuminated as compared to palis ade chloroplasts. Photoinhibition is shown to affect primarily the qua ntum yield of the palisade chloroplasts when excessive illumination is applied from the adaxial leaf side. The new system is envisaged to be used in combination with light measurements within leaves for an asse ssment of the specific contributions of different leaf regions to over all photosynthetic activity and for an integrative modelling of leaf p hotosynthesis.