Phospholipases Dζ1 and Dζ2 have distinct roles in growth and antioxidant systems in Arabidopsis thaliana responding to salt stress

Phospholipases D zeta play different roles in Arabidopsis salt tolerance affecting the regulation of ion transport and antioxidant responses. Lipid signalling mediated by phospholipase D (PLD) plays essential roles in plant growth including stress and hormonal responses. Here we show that PLD zeta 1 and PLD zeta 2 have distinct effects on Arabidopsis responses to salinity. A transcriptome analysis of a double pld zeta 1pld zeta 2 mutant revealed a cluster of genes involved in abiotic and biotic stresses, such as the high salt-stress responsive genes DDF1 and RD29A. Another cluster of genes with a common expression pattern included ROS detoxification genes involved in electron transport and biotic and abiotic stress responses. Total superoxide dismutase (SOD) activity was induced early in the shoots and roots of all pld zeta mutants exposed to mild or severe salinity with the highest SOD activity measured in pld zeta 2 at 14 days. Lipid peroxidation in shoots and roots was higher in the pld zeta 1 mutant upon salt treatment and pld zeta 1 accumulated H2O2 earlier than other genotypes in response to salt. Salinity caused less deleterious effects on K+ accumulation in shoots and roots of the pld zeta 2 mutant than of wild type, causing only a slight variation in Na+/K+ ratio. Relative growth rates of wild-type plants, pld zeta 1, pld zeta 2 and pld zeta 1pld zeta 2 mutants were similar in control conditions, but strongly affected by salt in WT and pld zeta 1. The efficiency of photosystem II, estimated by measuring the ratio of chlorophyll fluorescence (F (v)/F (m) ratio), was strongly decreased in pld zeta 1 under salt stress. In conclusion, PLD zeta 2 plays a key role in determining Arabidopsis sensitivity to salt stress allowing ion transport and antioxidant responses to be finely regulated.