Kinetics of Chlorophyll Degradation in Japanese Maple (Acer palmatum) Leaves with In Situ Heating Visible and Near-Infrared Spectroscopic Monitoring

Decreases in chlorophyll control the degradation of green plants during leaf senescence and fruit ripening processes. Our previous daily monitoring of the natural senescence processes of Japanese maple (<i>Acer palmatum</i>) leaves demonstrated initial slow and later fast chlorophyll (Chl) decrease rates. In this study, Chl decrease processes were monitored by in situ visible and near-infrared spectroscopy during heating of maple leaves to 30-200 °C. The initial decreases with time in the 640-720 nm band area, due mainly to chlorophyll a after the water decrease, were fitted by first-order kinetics. The obtained rate constants <i>k</i>₁ from 200 to 60 °C showed a quasi-linear trend on an Arrhenius plot with an activation energy <i>E</i>a of 38 kJ·mol^-1, while those from 60 to 30 °C had a different trend with an <i>E</i>a of 91 kJ·mol^-1. Since the previous natural faster Chl decrease rates are on the extension of the higher-temperature trend, this process might occur without the protection of proteins in the photosynthetic system. On the other hand, the previous natural slower Chl decrease rates are on the extension of the lower-temperature trend, and might have protein protection.