Changes in production of reactive oxygen species in illuminated thylakoids isolated during development and senescence of barley.

This paper presents a detailed analysis of thylakoids isolated from secondary barley leaves harvested 18, 22, 25, 29, 32, 35 and 39 days after sowing (DAS). Goal of the analysis was to investigate the production of different reactive oxygen species (ROS) during development and senescence of barley. Generation of superoxide anion (O2-•) and hydrogen peroxide (H2O2) increases during development of barley reaching the highest value right after the onset of senescence (between 25 and 29 DAS), thereafter the levels of both ROS start to decrease until 35 DAS when production of H2O2 increases again. In comparison with O2-• and H2O2, generation of singlet oxygen ((1)O2) showed continuous production of low amounts thought the duration of experiment. Oxidative damage to the thylakoid membrane was assessed by measuring lipid peroxidation. Results showed gradual increase in lipid peroxidation with progress of plant development with highest increase occurring at the late stages of senescence. A possible factor contributing to the elevation in the production of ROS could be an increase in membrane fluidity observed in our previous study. Fluidization of the membrane, allows for better penetration of oxygen inside the membrane, which can lead to an increase in the production of ROS. Indeed, the production of ROS started to increase together with observed fluidization of the membrane from 22 to 29 DAS. Thereafter, production of ROS started to decline till 35th DAS. On the last day of the measurement, chl is at 25% of its initial value, lipid peroxidation reaches the highest value and H2O2 increases again.