Effects of rare earth ions on activity of RuBPcase in tobacco

Abstract

To investigate the physiological effects of rare earth ions, we have studied the effect of LaCl 3 on the activity of ribulose 1,5-bisphosphate carboxylase (RuBPcase) in tobacco ( Nicotiana tobacum). When treated with 20–80 μmol/l LaCl 3 in Hoagland solution by water culture or by spraying with 400–1600 μmol/l LaCl 3 in pot experiment, the total and initial activities of RuBPcase were raised gradually, but decreased when the concentrations of LaCl 3 were ≥200 μmol/l in water culture and >1600 μmol/l by spraying. It was indicated that LaCl 3 promoted the activation of RuBPcase at low concentrations in vivo. It was also proved that lanthanides (Ln 3+) increased the activity of RuBPcase in vitro. Upon addition of different concentrations of Ln 3+ to replace Mg 2+, the RuBPcase activity exhibited an apparently biphasic response curve. Among the three Ln 3+ tested, the activation effects of La 3+ and Ce 3+ on RuBPcase were greater than that of Gd 3+, but the activation effects of all the three Ln 3+ were lower at high concentrations than that of Mg 2+, showing strongly inhibitory function. The extended X-ray absorption fine structure study of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco)–La complex indicated that La is bound with the oxygen atoms of amino acid residues, with the distance of the LaO bond being 2.51 Å. The mechanism of molecular interaction between Ln 3+ and RuBPcase is discussed.