The cytology and kinetics of cabbage root hair penetration by Plasmodiophora brassicae

Abstract

After a primary zoospore of Plasmodiophora brassicae attaches to a cabbage root hair wall, the flagella coil, and the axonemes are soon retracted. During the next 2 h a dense-staining bullet-like Stachel is formed within a tubular cavity in the cyst, the Rohr. Possibly because of pressure created within an expanding cyst vacuole, the Rohr is quickly evaginated to form a bulbous adhesorium. The Stachel punctures the host wall and then, in a period of about 1 s, the parasite is injected into the root hair. The total time required for adhesorium formation and host penetration is about 1 min. Secondary zoospores were found to be capable of carrying out a similar penetration process. After penetration a callose-rich papilla is soon formed between the host wall and plasma membrane at the penetration site. Young amoebae in root hairs have no lipid bodies and are surrounded by seven-layered envelopes. Unidentified spherical inclusion bodies were seen sporadically in primary zoospores and cysts, and in uninucleate amoebae.