Lycoris plants are extensively cultivated as ornamental plants in Japan and China. Some Lycoris (for example, a hybrid; L. traubii × L. sanguinea) plants grown in temperate zones are likely to show high sensitivity to high temperatures. We have investigated the effect of high temperatures on chlorophyll degradation in Lycoris plants, using leaf sections under 12 h-light and 12 h-dark conditions. A rapid decrease in chlorophyll levels was observed when all sections were exposed to continuous high temperature at 35°C or 45°C, in contrast to control sections at 15°C. The high temperature treatment (for 12 or 18 h at 35°C), followed by incubation at 20°C for 1 to 3 days induced significant chlorophyll degradation. Experiments using two kinds of protease inhibitors showed that 10 mM Phenylmethylsulfonyl fluoride (PMSF) and 4 mM N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) significantly suppressed the decrease in chlorophyll content and in the cell viability of leaf sections treated with the high temperature (35°C for 18 h). We found that the remarkable decrease in chlorophyll levels was followed by DNA laddering, which was induced by high temperature treatment at 35°C for 18 h. Other characteristic events, such as the activation of caspase-3-like activity and release of cytochrome c to the cytosolic fraction, were also observed in this system. These results implied that high temperatures accelerated leaf senescence, including the programmed cell death (PCD)-like phenomenon in Lycoris leaves.

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