Sugar starvation-induced synthesis and extracellular liberation of α-amylase molecules in suspension-cultured cells of rice (Oryza sativa L.) required Ca2+, although the level of translatable α-amylase mRNA was not affected in the presence of Ca2+. Sugar depletion markedly stimulated Ca2+ uptake by rice cells and sucrose supplementation reduced it. Immunohistochemical and electron probe microanalyzer studies indicated an apparent resemblance between the distribution pattern of Ca2+ and that of α-amylase molecules induced in the sugar-depleted cells. Ca2+ uptake was reduced by sucrose, maltose, fructose, and glucose similarly at more than 5 mM, but was unaffected by mannitol (88 mM), 6-deoxy-D-glucose (10 mM), and 3-O-methyl-D-glucose (10 mM). Furthermore, an effective Ca2+ channel blocker, La3+ significantly inhibited the Ca2+ uptake and the synthesis and extracellular liberation of α-amylase molecules in the absence of sucrose, while a general P-type ATPase inhibitor, vanadate greatly stimulated both in the presence of sucrose. We concluded that, by controlling the Ca2+ uptake, metabolic sugars regulate the protein synthesis and posttranslational secretory processes of α-amylase molecules in rice cells.