Abstract:To investigate the response of photosynthetic apparatus to UV-B radiation,we investigated the changes of chlorophyll fluorescence parameters under artificial simulated low UV-B radiation treatment(2.4 μW/cm2),that including Chl a fluorescence transients induced dynamic curve,F0,Fm,the parameters of PSⅡ reaction center activity(ABS/RC,TRo/RC and ETo/RC) and performance index (PI) in leaves of Glycyrrhiza uralensis,by using the pocket PEA.The results suggested that:(1)UV-B mainly influenced the acceptor side of PSⅡ system rather than its donor side because of the O-J-I-P chlorophyll fluorescence induction curves didn’t change by low level UV-B radiation.(2)The results of F0,Fm and Fv/Fm indicated that UV-B radiation inhibited the openness of reaction center and blocked the transporting of electron from QA to QB,and that was confirmed by the decreasing of PIabs and PItotal.Thus,low level UV-B radiation influences photochemical or non-photochemical reaction beyond QA as result of reduced electron transportation efficiency from QA to PQ.