Influence of water stress in different development stage on the citric acid metabolism-related genes expression in the Ponkan fruits

【Objective】To explore the influence of water stress within different development stage on or-ganic acid content and gene expression related to citrate metabolism in Ponkan fruit.【Methods】With 6-year potted trifoliate orange common Ponkan(Citrus reticulata Blanco)trees as test materials,regular wa-tering as control,five treatments along with the fruit growth process were arranged,including the wholeperiod,the earlier stage,the premetaphase stage,the medium-term stage and the later stage. The contentof acids in fruit were determined by HPLC,and relative expression of genes related to citric acid metabol-ic were determined by relative fluorescence quantitative PCR.【Results】Five treatment groups under wa-ter stress led to citric acid,malic acid,quinic acid and total acid concentration increased significantly.Relative expressions of Cit CS1 and Cit CS2 had all been raised to a certain extent. The relative expressionof Cit Aco1 was higher in overall,and relative expression of Cit Aco2 varied in different periods of treat-ments. However,relative expression of Cit Aco3 was declined to varying degrees. Relative expression of Cit IDH2 was the lowest in the three Cit IDH genes,but its all expression got the promotion. Relative ex-pression of Cit IDH1 varied under different treatment stage. The expression of Cit IDH3 was inhibited over-all. For the 2 Cit GAD genes,Cit GAD5 was activated earlier,the expressions of Cit GAD4,Cit GAD5 were inhibited under water stress at the different periods of treatment,the impact to Cit GAD5 was more signifi-cant.【Conclusion】Water stress within different development stages caused the accumulation of citric ac-id,increased total organic acid content,these changes were related to the changes of the relative expres-sions of genes telated to citric acid synthesis and degradation in the ponkan fruit. The down-regulation of Cit Aco3,Cit IDH3,Cit GAD4 and Cit GAD5 and up-regulation of Cit CS1,Cit CS2 might be one of the rea-sons why citric acid accumulated.