Effect of rare earth element europium on amaranthin synthesis in Amarathus caudatus seedlings

Considering the resemblances between Eu3+ and Ca2+ in their atomic radius and structures of the valence electron, the effects of Eu3+ on amaramthin synthesis in Amarathus caudatus seedling were studied. Eu3+ had both promoting and inhibiting effects on amaramthin synthesis. The optimum promoting concentration and half inhibiting concentration of Eu3+ to synthesis of amaranthin were 0.4 mmol/L and 2.5 mmol/L, respectively. In the dark, A23187 (ions carrier) could carry Eu3+ into cells through the Ca2+ channel. When Ca2+ was chelated with EGTA, the synthesis of amaranthin could be partly retrieved by Eu3+. Eu3+ treatment could also activate Ca2+- ATPase on plasma membrane. Moreover, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of total proteins from the plants treated by Eu3+ and Ca2+ were similar but slightly different in the contents. It suggested that the effects of Eu3+ and Ca2+ on amaranthin synthesis were similar. After being treated by Eu3+ or Ca2+, the outside Ca2+ could enter into cells to promote synthesis of amaranthin. The results above indicated that Eu3+ might replace Ca2+ in the calcium/calmidulindependent phytochrome signal transduction system and play important roles in plant development by promoting calcium transportation across plasma membrane.