SEASONAL FLUCTUATIONS OF ASCORBATE-RELATED ENZYMES - ACUTE AND DELAYED-EFFECTS OF LATE FROST IN SPRING ON ANTIOXIDATIVE SYSTEMS IN NEEDLES OF NORWAY SPRUCE (PICEA-ABIES L)

Seasonal changes of ascorbate peroxidase and monodehydroascorbate radi cal reductase activities were studied in foliar tissues of Norway spru ce (Picea abies L.), In mature needles, APX activities did not show se asonal fluctuations and were similar to those found in resting buds, M onodehydroascorbate radical reductase activity was higher in needles t han in buds and higher in winter than in summer. Maximum activities of both enzymes: were found before bud break and minimum activities In n ewly formed needles. When spruce seedlings were exposed to an artifica l frost event of -5 degrees C for one night in spring, ascorbate perox idase activity declined in young needles before the onset of visible i njury but corresponding to a sudden upsurge in lipid peroxidation, Aft er one week, some shoots showed severe symptoms of injury, some were s lightly injured and others did not show any visible injury. In lethall y injured needles, antioxidative protection (ascorbate peroxidase, mon odehydroascorbate radical reductase, glutathione reductase, glutathion e, ascorbate, superoxide dismutase) had collapsed, Surviving needles s howed a coordinated increase in all components of the antioxidative sy stem suggesting an efficient induction of defense systems. However, en hanced protection was observed only transiently, In fall, needles that had been exposed to frost in spring contained significantly less anti oxidants than unstressed needles indicating that unseasonal frost caus ed memory effects.