CHANGES IN SOME ANTIOXIDANT ENZYME ACTIVITIES IN HABERLEA RHODOPENSIS DURING DESICCATION AT HIGH TEMPERATURE

Haberlea rhodopensis (Gesneriaceae) is endemic plant in a very small group of poikilohydric angiosperms that are able to survive in an almost complete dehydrate state. Upon watering the plants rapidly revive and are restored to their former state. H. rhodopensis belongs to the homoiochlorophyllous type of desiccation tolerant plants that keep their chlorophyll content during drying. The high amount of chlorophyll molecules retained during desiccation could be a source for potentially harmful singlet oxygen production. That is why it was important to investigate the changes in the activity of some antioxidant enzymes during dehydration of Haberlea. Plants were desiccated at optimal (23 degrees C) and high (38 degrees C) temperature as drought stress is frequently accompanied by high temperatures under field conditions. The results showed that superoxide dismutase (SOD; EC 1.15.1.1) activity gradually decreased, whereas catalase (EC 1. 11. 1. 6) activity significantly increased during desiccation of Haberlea plants under both optimal and high temperature. Exposure of plants to high temperature reduced the activity of these enzymes. The enhanced activity of ascorbate peroxidase (APX; EC 1.11.1.11) and guaiacol peroxidase (GPX; EC 1.11.1.7) was observed under moderate water stress, after which they declined. High temperature stress applied alone did not influence the APX and GPX activity.