Brefeldin A Inhibits Secondary Cell Wall Synthesis in Developing Tracheary Elements ofZinnia elegans

Abstract

Brefeldin A (BFA) is an inhibitor that disrupts the organization and vesicle transport of the Golgi apparatus. The effects of BFA on the exocytotic pathway were tested on cells undergoing secondary cell wall synthesis. As a model system, isolated mesophyll cells of Zinnia elegans in liquid suspension culture were induced to differentiate into tracheary elements (TEs), a cell type characterized by its highly sculpted secondary wall thickenings. Disruption of vesicle transport from the exocytotic pathway was monitored indirectly as a function of wall deposition by staining cells with a fluorescent dye that binds to cellulose. Complete inhibition of TE differentiation occurred when BFA was added early in tracheary element formation at a concentration of 8 μg mL−1. Differentiation was seen in samples treated with the same concentration of BFA at later developmental stages. BFA‐inhibition of cell wall development was reversible. After a 4–5‐h exposure to and subsequent removal of BFA, differentiation resumed with 70% recovery. Treated cells showed a pronounced delay between time of BFA addition and inhibition of secondary wall synthesis. Electron microscopy of treated cells showed BFA also induced structural disruptions of the Golgi apparatus. The degree of disorder varied depending on the length of BFA exposure. These studies provide insight into the action and targets of BFA in differentiating plant cells and the role of the Golgi‐ER pathway during secondary cell wall synthesis.