Abstract: 【Objective】The objective of this study is to analyze the effect of Brassinosteroid (BR) on Ca²⁺distribution of plant cell, analyze the influence of BR on the expression level of the genes coding Ca²⁺ channel and Ca²⁺-ATPase, and clarify the effect of BR on calcium homeostasis in Arabidopsis thaliana. 【Method】The effect of BR on Ca²⁺ location in plant cell was studied using the potassium pyruantimonatc technique. The expression level of genes which coded Ca²⁺-ATPase (located in the membrane, vacuole, endoplasmic reticulum) and Ca²⁺ channel (located in membrane, vacuole, lysosome) was studied by Real-time PCR technique.【Result】Under normal condition, Ca²⁺ mainly distributed in cell walls, intercellular space, vacuole, and there were only a few Ca²⁺ distributed in the chloroplast and cytoplasm in plant cells. After 1 µmol·L^-1 BR treatment for 3 hours, Ca²⁺ gathered nearby vacuole membrane and cell membrane, meanwhile, the distribution of Ca²⁺ in the cytoplasm and chloroplast was increased. After BR treated for 6 hours, the Ca²⁺ distribution in the cytoplasm and chloroplast was continue increased, the Ca²⁺ distribution in the cell walls was reduced; after BR treated for 9 hours, the Ca²⁺ distribution in the cytoplasm and chloroplast was decreased, but increased in the intercellular space and vacuole, while the Ca²⁺ distribution in the cell walls was obviously reduced. It suggested that BR had function to release Ca²⁺ from cell wall. CNGC2 and CNGC12 are genes which encoded Ca²⁺ channel in the cell membrane. After 1 µmol·L^-1 BR treated for 3 hours, the expression level of CNGC2 and CNGC12 were all obviously decreased, this indicated that BR could block the extracellular Ca²⁺ transfer into cytoplasm. After 1 µmol·L^-1 BR treated for 6 hours, the expression levelsof CNGC2 and CNGC12 recovered；after 1 µmol·L^-1 BR treated for 9 hours, the expression levels of CNGC2 and CNGC12 were obviously increased. TPC1 and TPC2 are genes encoding Ca²⁺ channel in the vacuole and lysosome, respectively. The expression levels of TPC1 and TPC2 were significantly decreased after 1 µmol·L^-1 BR treated for 3 hours, but the TPC1 expression level was obviously higher than that without BR treated; the expression level of TPC2 was also significantly increased after 1 µmol·L^-1 BR treated for 9 hours. The results showed that BR could block the fast rising of the cytoplasm Ca²⁺ Concentrations, the expression level of the genes coding vacuole Ca²⁺ channel recovered earlier than that of the Ca²⁺ channel genes in the cell membrane and lysosome. ACA8 and ACA10 are genes encoding Ca²⁺-ATPase located in the cell membrane. After 1 µmol·L^-1 BR treated for 3 and 6 hours, the expression level of ACA8 and ACA10 had no significant change. After BR treated for 9 hours, the expression level of ACA8 and ACA10 was significantly increased. ACA4 and ACA11 were genes encoding Ca²⁺-ATPase located in the vacuole membrane, the change of ACA4 and ACA11 expression level was similar to the change of ACA8 and ACA10. ACA2 was one gene encoding Ca²⁺-ATPase located in the endoplasmic reticulum, the expression level of ACA2 also appeared the highest peak after 1 µmol·L^-1 BR treated for 9 hours. The results indicated that the expression level of Ca²⁺-ATPase genes increased after BR treated for 9 hours, and high concentrations cytoplasm Ca²⁺ was infused into extracellular and intracellular calcium store including intercellular space, vacuole, endoplasmic reticulum, etc. So BR could regulate the cytoplasm calcium homeostasis.【Conclusion】The second messenger Ca²⁺ was regulated by BR, and the signaling of BR was conducted through regulating the calcium homeostasis regulation system.

Key words: brassinosteroid, calcium, Ca²⁺ channel, Ca²⁺-ATPase; Arabidopsis thaliana