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A hydroponic experiment was conducted to investigate the effects of cadmium (Cd) on chlorophyll fluorescence and photosynthetic parameters on a Cd accumulating plant of Elsholtzia argyi. Four weeks-seedlings of E. argyi were treated with 0 (CK) 5, 10, 15, 20, 25, 30, 40, 50 and 100 μmol L(-1) Cd for 21 days. Fv/Fo, Fv/Fm, qP, ΦPSП, ETR and Fv'/Fm' were significantly increased under low Cd (5-15 μmol L(-1) for Fv/Fo, Fv/Fm and qP, 5-10 μmol L(-1) for ΦPSП, ETR and Fv'/Fm') stress, and these parameters were similar to control under Cd≤50 μmol L(-1). All above parameters were significantly decreased at 100 μmol L(-1) Cd. Compared with control, Pn was significantly (P<0.05) increased under 5-30 μmol L(-1) Cd. However, 50 and 100 μmol L(-1) Cd significantly (P < 0.05) reduced it. Gs and Tr were substantially decreased at 50-100 and 40-100 μmol L(-1) Cd, respectively. Ci was significantly increased at 50 and 100 μmol L(-1) Cd. High Cd-induced decrease of Pn is not only connected to stomatal limitation but also to the inhibition of Fv/Fo, Fv/Fm, ΦPSП, qP, ETR and increase of NPQ. Maintain chlorophyll fluorescence and photosynthesis parameters under its Cd tolerance threshold were one of tolerance mechanisms in E. argyi.

Main conclusion The molecular and physiological mechanisms of glycinebetaine stabilizing photosystem II complex under abiotic stresses are discussed, helping to address food shortage problems threatening the survival of growing population.