Antioxidative enzyme activity as the factor causing differential autumn senescence in phenological forms of beech (Fagus sylvatica L.)

Abstract

Reactive oxygen species affect the timing and rate of leaf senescence in different phenological forms of beech. We investigated the contribution of the enzymatic part of the antioxidative system in controlling the induction and course of this process. Leaf senescence was associated with differential dynamics of protein degradation and increased accumulation of the superoxide ion (O 2 ·− ) and hydrogen peroxide (H2O2). The different phenological forms and temperature courses over the sampling periods significantly affected the level and profile of antioxidative enzyme activity. Except for catalase (CAT), the activity of antioxidative enzymes (superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) in the pre-senescence stage was highest in the late form. Diverse responses to decreased temperature caused differential rates of decrease in antioxidative enzyme activity. While CAT and MDHAR activity decrease was continuous, characteristic of phenological forms and showed a time shifting, the decrease in SOD, APX, and GR activity was reversible during the temperature increase in the initial stage of senescence and dependent on phenological form. In the final stage of senescence, enzyme activity decrease was quick, was irreversible, and was less influenced by temperature. Changes in antioxidative enzyme activity resulted in greater tolerance to oxidative stress and lower rates of leaf senescence in the late phenological form. Based on current and previous studies, the hypothetical model for slower leaf senescence in late phenological forms of beech was demonstrated.