Cellular distribution of calmodulin and calmodulin-binding proteins in Vicia faba L

The distribution of calmodulin (CaM) and CaM-binding proteins within Vicia faba was investigated. Both CaM and CaM-binding proteins were found to be differentially distributed among organs, tissues, and protoplast types. CaM levels, on a per protein basis, were found to be the highest in leaf epidermis, containing 3-fold higher levels of CaM than in total leaf. Similarly, guard cell and epidermal cell protoplasts were also found to have higher levels of CaM than mesophyll cell protoplasts. ¹²⁵I-CaM blot overlay assays were performed to qualitatively examine CaM-binding proteins in these protoplast types as well as in whole tissues and organs. CaM-binding proteins with M, 52,000, 78,000, and 115,000 were common in all metabolically active plant parts. Unique CaM-binding protein bands were detected in guard cell protoplasts (M, 39,000, 88,000), stems (M, 45,000, 60,000, 64,000), and roots (M, 62,000), suggesting the presence of specialized CaM-dependent processes in these cells and organs.