Extracellular ATP affects chlorophyll fluorescence of kidney bean (Phaseolus vulgaris) leaves through Ca²⁺ and H₂O₂-dependent mechanism

Abstract

Extracellular ATP (eATP) has been considered as an important extracellular compound to mediate several physiological processes in plant cells. We investigated the effects of eATP on chlorophyll (Chl) fluorescence characteristics of kidney bean (Phaseolus vulgaris) leaves. Treatment with exogenous ATP at 1 mM showed no significant effect on the maximal photochemical efficiency of PSII. However, the treatment significantly enhanced the values of the PSII operating efficiency (Φ PSII ), rate of photosynthetic electron transport through PSII (ETR), and photochemical quenching (q P ), while the values of the nonphotochemical quenching (q N ) and quantum yield of regulated energy dissipation of PSII (Y NPQ ) significantly decreased. Our observations indicated that eATP stimulated the PSII photochemistry in kidney bean leaves. Similarly, the treatment with exogenous Ca 2+ or H 2 O 2 at 1 mM caused also the significant increase in Φ PSII , q P , and ETR and the significant decrease in q N and Y NPQ . LaCl 3 (an inhibitor of Ca 2+ channels) and dimethylthiourea (a scavenger of H 2 O 2 ) abolished the effects of exogenous ATP. The results suggest that the role of eATP in enhancing the PSII photochemistry could be related to a Ca 2+ or H 2 O 2 signaling pathway.