Analysis of effects of abscisic acid on Cucumis sativus L. leaves using chlorophyll fluorescence imaging and thermal imaging

An image instrumentation system capable of quantitative analysis of chlorophyll (Chl) fluorescence images and thermal images was developed. Using this system, measurements of Chl fluorescence images and thermal images were performed on attached Cucumis sativus L. leaves during 10-3 M abscisic acid (ABA) treatment. Images of quenching parameters, such as qP, qN, NPQ and Yield were calculated from Chl fluorescence images obtained by the saturation pulse method. Images of stomatal conductance were computed by a method developed by Omasa et al. (1981) from leaf temperature images. Stomatal conductance immediately decreased by ABA treatment. However, the quenching parameters did not change during 75 min after the treatment, showing that ABA primarily induced a decrease in stomatal conductance and did not affect intercellular CO2 mole fraction (Ci). Following the 75 min period, the quenching parameters changed gradually. For example, photochemical efficiency of photosystem II decreased because of the declining CO2 supply to the site and the decrease in Ci in conjunction with the decrease in stomatal conductance. Consequently, it was shown that simultaneous use of Chl fluorescence image analysis and thermal image analysis was effective for analyzing the heterogeneous response and patchy distribution of stomatal aperture and photosynthesis.