Abstract: The effects of 5 mg/L 1,2,4-trichlorobenzene (TCB) and 0.1 mmol/L mercury ion (Hg²⁺) stresses on Ca²⁺ fluxion and protein phosphorylation in rice seedlings were investigated by isotope exchange kinetics and in vitro phosphorylation assay. The Ca²⁺ absorption in rice leaves and Ca²⁺ transportation from roots to leaves were promoted significantly in response to Hg²⁺ and TCB treatments for 4-48 h. The Ca²⁺ absorption peaks presented in the leaves when the rice seedlings were exposed to Hg²⁺ for 8-12 h or to TCB for 12-24 h. Several Ca²⁺ absorption peaks presented in the roots during rice seedlings being exposed to Hg²⁺ and TCB, and the first Ca²⁺ absorption peak was at 8 h after being exposed to Hg²⁺ and TCB. The result of isotope exchange kinetic analysis confirmed that short-term (8 h) Hg²⁺ and TCB stresses caused Ca²⁺ channels or pumps located on plasmalemma to open transiently. The phosphorylation assay showed that short-term TCB stress enhanced protein phosphorylation in rice roots (TCB treatment for 4-8 h) and leaves (TCB treatment for 4-24 h), and short-term (4-8 h) Hg²⁺ stress also enhanced protein phosphorylation in rice leaves. The enhancement of protein phosphorylation in both roots and leaves corresponded with the first Ca²⁺ absorption peak, which confirmed that the enhancement of protein phosphorylation caused by TCB or Hg²⁺ stress might be partly triggered by the increases of cytosolic calcium. TCB treatment over 12 h inhibited protein phosphorylation in rice roots, which might be partly due to that TCB stress suppressed the protein kinase activity. Whereas, Hg²⁺ treatment inhibited protein phosphorylation in rice roots, and Hg²⁺ treatment over 12 h inhibited protein phosphorylation in rice leaves. This might be attributed to that not only the protein kinase activity, but also the expressions of phosphorylation proteins were restrained by Hg²⁺ stress.

Key words: rice, mercury ion, 1,2,4-trichlorobenzene, calcium ion fluxion, protein phosphorylation