High-temperature conditions were applied during the daytime only, for 10 h, while night temperatures were a moderate 18 8C. For application of the high-tempera- ture conditions of 39 8C, an apparatus was built including a heater, thermostat and humidifier, enabling control of temperature and humidity (kept the same as the phytotron room, at 60%). For temperature treat- ment of whole plants, the plant table was covered with a transparent polyethylene sheet.