Abstract: We studied the systemic effects of extracellular ATP(eATP) on the Photosystem Ⅱ photochemistry of kidney bean(Phaseolus vulgaris) leaf and possible mechanism for this effect. Treatment of a half of a bean leaf with exogenous ATP had no significant effect on the maximal photochemical efficiency of photosystem Ⅱ(F_v/F_m), and the quantum yield of non-regulated energy dissipation(Y(NO)) of the treated half and the untreated, opposite half of the same leaf. However, this treatment significantly increased the values of photochemical efficiency(Y(Ⅱ)), the rate of photosynthetic electron transport(ETR), and photochemical quenching(qP), while the values of the non-photochemical quenching(qN) and the quantum yield of regulated energy dissipation(Y(NPQ)) were significantly decreased by exogenous 1 mmol·L^-1 ATP. These observations indicate that eATP can function in systematically enhancing the PSⅡ photochemistry of kidney bean leaves. Treatment of a half of a bean leaf with exogenous ATP, we tested the change of the oxidation hydrogen content of the treated half and the untreated, opposite half of the same leaf. Compared to the control, hydrogen peroxide content of the treated half and the untreated, opposite half of the same leaf were significantly increased. Similar to the effects of exogenous ATP, treatment with exogenous H₂O₂ at 1 mmol·L^-1 also led to a significant increase in Y(Ⅱ), qP and ETR and a significant decrease in qN and Y(NPQ) of the treated half and the untreated, opposite half of the same leaf. DMTU(dimethylthiourea, a scavenger of H₂O₂) weakened the effects of exogenous ATP on the Y(Ⅱ)), qP, ETR, qN and Y(NPQ). These observations indicate that an increase in eATP concentration of partial region of bean leaf can enhance the PSⅡ photochemistry of the adjacent tissues, and such function of eATP could be dependent of H₂O₂.

Key words: chlorophyll fluorescence, extracellular ATP, exogenous H₂O₂, kidney bean(Phaseolus vulgaris), systemic