Abstract:To reveal the defense mechanism of anthocyanins under salt stress, the physiological responses to NaCl stress in three Arabidopsis mutants (tt3, tt4 and tt3tt4) deficient in anthocyanin biosynthesis and wild type (WT) plants were studied. The mutants tt3, tt4 and tt3tt4 are deficient in dihydroflavonol 4-reductase gene (DFR), chalcone synthase gene (CHS) and both DFR and CHS, respectively, these genes encode enzymes that act in the anthocyanin biosynthesis pathway. The results showed that, under salinity stress, the three mutants with lower anthocyanin accumulation exhibited greater reductions in PSII maximum quantum yield (Fv/Fm), effective quantum yield (Yield), electron transport rate (ETR), photochemical quenching (qP) and non-photochemical quenching (NPQ) and greater increases in lipid peroxidation, than the WT. Histochemical stains with nitroblue tetrazolium (NBT) showed that superoxide anion free radical (O2·-) in tt3tt4 was the highest, followed by tt3 or tt4, and then by WT. These suggest that anthocyanins play an important role in plant adaptations to salinity stress, possibly via serving as a kind of osmo-regulator and antioxidant. Therefore, anthocyanin contents can be used as an indicator for screening of salt-tolerant crops.