Comparative study on energy partitioning in photosystem II of two Arabidopsis thaliana mutants with reduced non-photochemical quenching capacity

Lhcb1-2 and PsbS proteins of photosystem II (PSII) have important roles in photoprotective thermal energy dissipation of the absorbed excess light energy. The light responses of chlorophyll fluorescence parameters were analyzed to examine how the absence of Lhcb1-2 or PsbS proteins can modify the energy allocation patterns of absorbed light energy in PSII using an antisense construct of lhcb2 and a psbS deletion (npq4-1) mutant of Arabidopsis thaliana. Both mutants exhibit reduced Stern-Volmer non-photochemical chlorophyll fluorescence quenching (NPQ). Here, we have adopted an approach, presented by Hendrickson et al. (Photosynth Res 82:73-81, 2004), to gain a better insight into the mechanism of the NPQ in these mutants. We have found no significant differences in the quantum yields of photochemical energy conversion (I broken vertical bar(PSII)) between the mutants and the wild type. Nevertheless, as it was expected, the fraction of the energy, which is dissipated as heat via regulated pathways in PSII (I broken vertical bar(NPQ)) for both mutants, were reduced as compared to the wild type. In a complementary way, the extent of non-regulated non-photochemical energy loss in PSII (I broken vertical bar(NO)) for both mutants was significantly higher than that in the wild type. This reflects, together with the lower I broken vertical bar(NPQ) (or NPQ) values, suboptimal capacity of photoprotective reactions at higher light intensities.