Abstract: Effect of La on the chlorophyll content of Soybean(Glycine max) seedling under elevated ultraviolet-B radiation(UV-B,280-320 nm) was studied.When seedling was pretreated by La(Ⅲ),the content of the interim outcomes of the chlorophyll such as δ-amino-laevulic acid(ALA),proto bile pigment(PBG),proto-porphyrin-IX(Proto-IX) and magnesium protoporphyrin(Mg-Proto) increased,and the process from protochlorophyll to chlorophyll was accelerated.The La(Ⅲ) promoted the protective effect of plant against UV-B stress through delaying the form of the PBG,Proto-IX,Mg-Proto and ALA.Therefore,the chlorophyll biosynthesis was suffocated under the condition of UV-B stress.The restrained location was from ALA to PBG.

Key words: Lanthanum(La), Lanthanum(La), Ultraviolet-B radiation, Chlorophyll biosynthesis and degradation