Chlorophyll Metabolism of Spinach Leaves under Seawater Stress

The effects of seawater stress on chlorophyll metabolism of two spinach cultivars,Helan No.3(seawater tolerant cultivar) and Yuanye spinach(seawater sensitive cultivar) were investigated by hydroponics.The results showed that the contents of chlorophyll b(Chl b),chlorophyll a(Chl a),Chl(a+b) and precursor of Chl such as protochlorophyll(Pchl),Mg-protoporphyrin IX(Mg-proto IX),protoporphyrin IX(Proto IX) and uroorphyrinogen III(UroIII) in two spinach cultivars were decreased significantly,whereas porphobilinogen(PBG) and δ-aminolevulinic acid(ALA) were increased significantly under seawater stress.The change range is greater in cv.Yuanye than that in cv.Helan No.3.The activity of chlorophyllase(Chlase) was not influenced in the leaves of Helan No.3 under seawater stress,whereas activities of porphobilinogen deaminase(PBGD) and uroporphyrinogen III synthase(UROS) were decreased significantly on the third day of treatment.As to cv.Yuanye,PBGD and UROS were decreased significantly with the chlase activity increasing significantly.The results showed that chlorophyll biosynthesis in leaves of two spinach cultivars was blocked by seawater stress at the step from PBG to UroIII,and cv.Yuanye was more susceptible to seawater than Helan No.3.The decrease of Chl in cv.Helan No.3 was caused by block of chlorophyll synthesis,whereas the reasons of the decrease of Chl in cv.Yuanye were block of chlorophyll synthesis and accelerating degradation of chlorophyll.