Comparative photoinhibition of a high and a low altitude ecotype of tomato (Lycopersicon hirsutum) to chilling stress under high and low light conditions

A high altitude ecotype and a low altitude ecotype of tomato (Lycopersicon hirsutum) plants were examined to compare their capacities to resist chilling-induced photoinhibition. Tomato plants at 5 weeks old were acclimated under high light condition of 550 μmol m^-2 s^-1 at 25/20°C (day/night) for 3 days. Acclimated plants were exposed to a temperature of 5/5°C for 3 days with either low light (60 μmol m^-2 s^-1) or high light (550 μmol m^-2 s^-1). The plants were allowed to recover under the same conditions as in the acclimation. The low altitude ecotype exhibited significantly greater decrease in both quantum yield for O₂ evolution and chlorophyll a fluorescence than the high altitude ecotype after 3 days of chilling. This tendency became more obvious under high light than under low light condition during the chilling. When both ecotypes were exposed to high light during the chilling, the high altitude ecotype accumulated more carotenoid pigments including zeaxanthin than the low altitude ecotype. In chilling at low light, however, their capacities to accumulate the carotenoid pigments were not different. Our results suggest that the high altitude ecotype has a greater capacity to develop its photosynthetic apparatus to resist chilling-induced photoinhibition through the accumulation of zeaxanthin as well as photochemical energy dissipation than the low altitude ecotype, but the non-radiative energy dissipation is required less during chilling under low light condition.