The light induced production of the O•
2− was measured in a
DMPO/DMSO reaction mixture. The O•
2− generated during the illumination
reacts with the DMPO spin trap creating a DMPO-OOH
spin adduct which can be detected with EPR. Fig. 3 represents
typical spectra of DMPO-OOH superoxide anion radicals measured
in thylakoids illuminated with 500 mol quanta m−2 s−1 of
white light isolated from barley leaves of different ages. Simulation
of spectra was performed, resulting in correlation coefficient
0,9635 which confirms that obtained spectra belongs to superoxide
anion radicals. Obtained hyperfine splitting parameteres were:an1 = 12,899; ah1 = 10,335; ah2 = 1357. The values of O•
2− produced
during barley development were expressed by evaluating
the height of the signal recorded in different samples, shown in
Fig. 4. The production of O•
2− increases during the development of
barley and reaches the highest value 29 DAS, which is right after
the onset of senescence (between 25 and 29 DAS) if we take chl
content as reference marker (Fig. 1A). Thereafter, the production of
O•
2− starts to gradually decrease.