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.)

Abstract

Seasonal changes of ascorbate peroxidase and monodehydroascorbate radical reductase activities were studied in foliar tissues of Norway spruce {Picea abies L.). In mature needles, APX activities did not show seasonal fluctuations and were similar to those found in resting buds. Monodehydroascorbate radical reductase activity was higher in needles than in buds and higher in winter than in summer. Maximum activities of both enzymes were found before bud break and minimum activities in newly formed needles. When spruce seedlings were exposed to an artifical frost event of — 5°C for one night in spring, ascorbate peroxidase activity declined in young needles before the onset of visible injury but corresponding to a sudden upsurge in lipid peroxidation. After one week, some shoots showed severe symptoms of injury, some were slightly injured and others did not show any visible injury. In lethally injured needles, antioxidative protection (ascorbate peroxidase, monodehydroascorbate radical reductase, glutathione reductase, glutathione, ascorbate, superoxide dismutase) had collapsed. Surviving needles showed a coordinated increase in all components of the antioxidative system suggesting an efficient induction of defense systems. However, enhanced protection was observed only transiently. In fall, needles that had been exposed to frost in spring contained significantly less antioxidants than unstressed needles indicating that unseasonal frost caused memory effects.