Calmodulin and its role in the secretory apparatus of the desmid Closterium

Closterium acerosum is a large bipolar desmid that has an extensive secreto ry apparatus. Two major secretory complexes that are produced by this green alga are a glucuronic acid-rich mucilage that is key in the gliding mechan ism and a cell wall consisting of multiple polysaccharide and protein compo nents. These substances are synthesized and processed for secretion through an elaborate endomembrane system and are transported around the cell and t o the cell surface via actin-mediated cyclosis. In this study, an analysis of the role of calmodulin with regard to the secretory apparatus was conduc ted. Whole-cell extracts and Western blot analysis show the existence of ca lmodulin. Immunogold labeling reveals calmodulin in the peripheral cytoplas m near the plasmamembrane and cell wall region. Calmodulin antagonists caus e significant disruption to the morphology of the Golgi apparatus. On appli cation of the antagonists W7, W13, TMB-8, and TFP, the Golgi body exhibits reduction in the number of cisternae per stack, significant curling of cist ernae, and formation of unusual multiperforate vesicles. In addition, there is alteration of the cytoplasmic streaming network and limited disturbance to the peripheral vacuole system. Immunogold labeling with an antibody spe cific to the mucilage shows that mucilage processing is still apparent in t he altered Golgi bodies and remnants after treatment.