The Accelerated Effects of AK-Toxin I on Exocytosis and Endocytosis of Susceptible Japanese Pear Leaves

Abstract

A host-specific toxin (AK-toxin I) from Alternaria alternata Japanese pear pathotype has the ability to cause production of abundant carbohydrates in host cells in addition to plasma membrane modifications associated with permeability changes. A cytochemical study for detection of cellular ions in toxin-treated host cells showed that plasmodesmatal plasma membranes were the sites of ion-leakage, indicating that they were compatible with the attacked sites of the toxin. The carbohydrates were shown immunoelectron microscopically to contain β-1,3 glucan. The glucan was assembled in the trans-Golgi network (TGN) of Golgi apparatus and transported with exocytotic Golgi vesicles from TGN to the invaginated sites, i.e., the damaged plasma membranes at plasmodesmata. Many exocytotic vesicles were fused with plasmodesmatal plasma membranes and the glucan inside the vesicles was released to the invaginated sites. By accumulating the glucan, the plasma membranes became invaginated towards the cytoplasm. A large number of smooth tubules and many multivesicular bodies (MVB) were found in the toxin-treated host cells with abundant carbohydrates. The tubules were identified as partially coated reticulum (PCR) of Golgi apparatus because they involved some clathrin vesicles and no Golgi matrix. The MVB were more abundant in toxin-treated than in water-treated host cells. Taking account of the functions of PCR and MVB together with the results obtained, the PCR and MVB appeared to serve for re-cycling of the excessive membrane in plasma membranes in the encocytotic pathway. The toxin caused activation in function of both exocytosis and endocytosis of host cells.KeywordsGolgi ApparatusTrans Golgi NetworkAlternaria AlternataJapanese PearGolgi VesicleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.