Laser-induced chlorophyll fluorescence measurement system to assess photosynthetic status within leaves

Chlorophyll (Chi) fluorescence measured on a leaf surface only provides the photosynthetic status of chloroplasts near the surface due to self-shading effect of Chi. Here, we report a laser-induced Chi fluorescence measurement system, which enables measurement of fluorescence induction kinetics at different tissues within a leaf as well as on both leaf surfaces, to assess photosynthetic status within leaves. The logarithmic time-scaled Chi fluorescence induction kinetics obtained from Chenopodium album leaves showed polyphasic transients in which four inflection points designated as O, J, I and P, were observed. Adaxial surface and palisade mesophyll showed significantly higher fluorescence intensities at O than abaxial surface and spongy mesophyll, respectively. In contrast, fluorescence intensities at J, I and P were significantly higher at abaxial surface and spongy mesophyll. Using these fluorescence intensities, the JIP test was performed. The results of JIP test indicated that adaxial surface and palisade mesophyll are characterized by lower maximum quantum yield of photosystem II (PSII) and net rate of PSII closure, but higher rate of energy transfer into electron transport chain than abaxial surface and spongy mesophyll. Considering these dorsiventral and intra-leaf variations in Chi fluorescence parameters, this study suggested the necessity of Chi fluorescence measurements on tissues as well as both surfaces to evaluate photosynthetic status of a whole leaf.