Arabidopsis gun4 mutant have greater light energy transfer efficiency in photosystem II despite low chlorophyll content

Arabidopsis gun4 mutant is defected in retrograde signaling and is characterized by reduced levels of chlorophyll. However, the impact of this mutation on plant photosynthetic performance remains unclear. We carried out a physiological characterization of gun4 in order to investigate the role of GUN4 for plant photosynthetic performance under light stress. The gun4 plants showed reduced minimal fluorescence in dark-adapted leaves and quantum yield of unregulated energy dissipation of photosystem II (PSII) under non-light-stress condition. The effective quantum yield of the PSII (Phi(PSII)) and photochemical quenching (qL) were higher in gun4 plants. Higher values of Phi(PSII) were also observed in gun4 under different light intensities. However, the rate of net carbon assimilation and stomatal conductance were lower in gun4. No differences were detected between the genotypes in the total absorption of (CO2)-C-14 as well as in the percentage of C-14 flux to basic amino acids, sugars, starch, and cell wall. After light stress, the potential quantum yield of PSII decreased only in wild type and the non-photochemical quenching was higher in gun4. Taken together, the results suggest that gun4 transfers more efficiently the excess of light energy absorbed despite a reduction in chlorophyll and carotenoids content and has greater capacity to dissipate the excess of energy absorbed.