*To whom correspondence should be addressed.
Received April 23, 2019; Revised May 23, 2019; Accepted May 23, 2019
Changes in the light energy distribution between the photosystems 1 and 2 (PS1 and PS2, respectively) due to the reversible migration of a part of the light-harvesting complex (LHC2) between the photosystems (state transitions) have been studied in leaves of barley and Arabidopsisplants upon short-term illumination with light of various intensity that excited predominantly PS2. Changes in the ratio of fluorescence maxima at 745 and 685 nm in the low-temperature (77 K) fluorescence spectrum of chlorophylla(Chla) characterizing energy absorption by the PS1 and PS2, respectively, were insufficient for revealing the differences in the STs in barley and Arabidopsisplants at various light intensities, because they were not associated with STs at high-intensity illumination. Light-induced accumulation of the LHC2 phosphorylated proteins Lhcb1 and Lhcb2 involved in the relocation of a part of the LHC2 from PS2 to PS1 in the leaves of both plants decreased with the increase in the light intensity and was more pronounced in barley than inArabidopsisat the same light intensity. Relaxation of the non-photochemical quenching (NPQ) of Chl afluorescence after illumination corresponding to the return of the part of LHC2 from PS1 to PS2 was observed in barley leaves in a wider range of increasing light intensities than in Arabidopsisleaves. The differences in the accumulation of phosphorylated Lhcb1 and Lhcb2, as well as in the parameters of NPQ relaxation after illumination, revealed that STs in barley leaves could occurnot only at low-but also at high-intensity light, when it is absent inArabidopsisleaves.
KEY WORDS: Arabidopsis, barley, photosynthesis, phosphorylation of antenna proteins, chlorophyllafluorescence