Calcium plays important roles in cell signal transduction,and Ca²⁺-binding proteins participate in various activities.There is much Ca²⁺ in extracellular space than that in cytoplasm,so the researches on extracellular Ca²⁺-binding proteins has an important meaning.First,extracellular proteins were prepared from the suspension-cultured cells of Arabidopsis thaliana,then separated by SDSPAGE and transferred to nitrocellulose membranes.The membranes were blotted with ⁴⁵Ca²⁺,and then exposed to phosphimager.Four protein bands each with molecular weight about 17,30,40,68 ku were shown.These proteins may function extracellularly with Ca²⁺.