Differences of Free Salicylic Acid Content and RootMorphology in Arabidopsis Wild-type andMutant sex1 under Environmental Stresses

Changes on free salicylic acid(SA) were researched in 10 different growth-stages of Arabidopsis thaliana wild type(WT).Differences of free SA and seedling root morphology in WT and mutant sex1 upon treatments with Pst.DC3000(Pseudomonas syringae pv.tomato DC3000),H2O2,MV(methyl viologen) and SA were analyzed by HPLC and microscope methods.The results showed that the level of free SA in WT was the lowest in flower production(6.30 and 6.50) and silique ripening(8.0) growth-stages.After 2 mmol·L-1 SA treatment,we found that free SA levels both in sex1 and in WT were higher than that of other treatments.However,free SA content in sex1 was higher than in WT and it was about 10 times compared with other treatments.Under MV and H2O2 stresses,there were no significant differences in the main root growth.Treated by low concentration of MV,it showed that sex1 seedlings had longer root hairs than WT seedlings,whereas there were no differences in the root hair density between WT seedlings and sex1 seedlings.While treated by low concentration of H2O2,the differences of the root hair in WT and sex1 seedlings were similar to control group.However,upon different concentrations of SA treatments,the differences of the main root growth between WT and sex1 seedlings became more prominent,especially when seedlings grew on 10 μmol·L-1 SA media in Petri plates.Interestingly,the root hair of WT and sex1 seedlings gradually missed from high concentration of SA treatment to low concentration of SA treatment,but it was more distinct in sex1 seedlings.Therefore,these results suggested that maybe it had some relationships between plant flowering,seed harvesting and SA-dependent pathway.Exogenous SA could accelerate more free SA production in sex1 which compared with other treatments by Pst.DC3000,H2O2 and MV.Root development of sex1 seedlings was more sensitive on growth environment than that of WT seedlings.In addition,root morphology of sex1 seedlings was in a SA concentration-dependant manner.