Reactive oxygen species and antioxidant levels as the factors of autumn senescence in phenological forms of beech (Fagus sylvatica L.)

This study examines changes in the reactive oxygen species (ROS) content and in the level and degree of ascorbate and glutathione oxidation during leaf senescence in phenological forms of beech (Fagus sylvatica L.). Leaves were collected between August and October in 2009 and 2012. Chlorophyll degradation depended significantly on the phenological characteristics of the specimens. Chlorophyll, proteins, superoxide ion and hydrogen peroxide contents and lipid peroxidation dynamics exhibited greater dependence on temperature changes in the early form than in the late form. In the early stage of senescence, the late beech form presented a greater increase in ascorbate and glutathione synthesis than did the early form (ascorbate and glutathione synthesis was the main characteristic of the phenological forms' defence mechanism against increasing ROS concentration). The early form was characterized by a stronger correlation between increasing ROS and the concentrations of oxidized forms of ascorbate and glutathione. We conclude that the earlier onset and greater rate of autumn senescence in the early phenological form relative to the late form were associated with significantly quicker chlorophyll degradation and greater production of ROS, which was better balanced by the antioxidant system in the late phenological form. The different concentrations of ascorbate and glutathione and the degree of their oxidation influenced the oxidative stress tolerance in the senescing leaves of the different phenological forms of beech.