Abstract: Effects of NaHSO₃ on the changes of photosynthetic rate, Hill reaction rate, pigment content and the parameters of chlorophyll fluorescence under enhanced UV-B radiation were investigated in spinach leaves. The results were as follows: The content of p igment, net photosynthetic rate, conversion efficiency of primary light energy ( Fv/Fm ) of PSⅡ, the photochemical quenching coefficient ( q_P ) , the non2photochemical quenching coefficient ( qN ) , the quantum yield of PSⅡelectron transport (ΦPSⅡ ) and the Hill reaction rate were decreased while Chl. a /b, Car. /Chl. were enhanced by UV-B stress. Under the combined treatment of enhanced UV-B radiation and NaHSO₃ , NaHSO₃ could significantly alleviate the inhibition of high dosage
UV-B treatment while imp roved little at low dosage UV-B radiation on the indexes above. It was suggested that the positive effects of NaHSO₃ could lighten the negative effects of UV-B radiation treatment as UV-B radiation
became intensified. It is a primary reason of net photosynthetic rate enhancing that the Chl. a content, Hill reaction rate, Fv /Fm andΦPSⅡ were increased by combined treatment.

Key words: spinach, NaHSO₃, UV-B radiation, photosynthetic rate, Hill reaction, chlorophyll fluorescence