~) 1996 Kluwer Academic Publishers. Printed in the Netherlands. Technical communication Measurement of chlorophyll fluorescence within leaves using a modified

optic microsensor By using a fiber-optic microprobe in combination with a modified PAM Fluorometer, chlorophyll fluorescence yield was measured within leaves with spatial resolution of approximately 20 #m. The new system employs a miniature photomultiplier for detection of the pulse-modulated fluorescence signal received by the 20 #m fiber tip. The obtained signal/noise ratio qualifies for recordings of fluorescence induction kinetics (Kautsky effect), fluorescence quenching by the saturation pulse method and determination f quantum yield of energy conversion at Photosystem II at different sites within a leaf. Examples of the system performance and of practical applications are given. It is demonstrated that he fluorescence rise kinetics are distinctly faster when chloroplasts within the spongy mesophyll are illuminated as compared to palisade chloroplasts. Photoinhibition is shown to affect primarily the quantum 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 assessment of the specific ontributions ofdifferent leaf regions to overall photosynthetic activity and for an integrative modelling of leaf photosynthesis