Effect of heat stress on subsequent chlorophyll accumulation in seedlings of Colocynthis citrullus.

When 14-day-old, etiolated seedlings of Colocynthis citrullus were subjected to temperatures of 35, 40 or 45°C for 4-24 h in darkness and illuminated immediately after this heat stress, the rate of total chlorophyll accumulation was retarded, and the duration of the initial lag period before onset of appreciable chlorophyll accumulation was prolonged. These effects were more pronounced after the higher temperatures, and with increasing duration of stress. Chlorophyll a and chlorophyll b were similarly affected as total chlorophyll.