The lack of LHCII proteins modulates excitation energy partitioning and PSII charge recombination in Chlorina F2 mutant of barley

Analysis of the partitioning of absorbed light energy within PSII into fractions utilized by PSII photochemistry (Ø_PSII), thermally dissipated via ΔpH-and zeaxanthin-dependent energy quenching (Ø_NPQ) and constitutive non-photochemical energy losses (Ø_NO) was performed in wild type and F2 mutant of barley. The estimated energy partitioning of absorbed light to various pathways indicated that the fraction of Ø_PSII was slightly higher, while the proportion of thermally dissipated energy through Ø_NPQ was 38% lower in F2 mutant than in WT. In contrast, Ø_NO, i.e. the fraction of absorbed light energy dissipated by additional quenching mechanism(s) was 34% higher in F2 mutant. The increased proportion of Ø_NO correlated with narrowing the temperature gap (ΔT_M) between S_2/3Q_B− and S₂Q_A− charge recombinations in F2 mutant as revealed by thermoluminescence measurements. We suggest that this would result in increased probability for an alternative non-radiative P680+Q_A− radical pair recombination pathway for energy dissipation within the reaction centre of PSII (reaction center quenching) and that this additional quenching mechanism might play an important role in photoprotection when the capacity for the primary, zeaxanthin-dependent non-photochemical quenching (Ø_NPQ) and state transitions pathways are restricted in the absence of LHCII polypeptides in F2 mutant.Key words: Energy partitioning, Non-photochemical quenching, Hordeum vulgare L., PSII photochemistry, Q_A, Q_B, Thermoluminescence