Figure 19.

Diagrammatic representation of root hair microbe protoplast ejection. Microbes in tips are red to indicate superoxide exposure and nitrogen extraction; microbes cycling in hairs are blue to indicate replication and nitrogen fixation. (A) Cyclosis moves microbes to the periplasmic space at the top of the hair where they accumulate and secrete ethylene en mass. (B) Microbial ethylene triggers a growth spurt in the hair which manifests as an expansion wave that propagates from the base to the tip of the hair. The expansion wave (red arrow) causes growth in the hair and forces out the bacteria accumulated in the hair tip. (C) The remaining bacteria are taken back into the cyclosis stream and replicated. (D) As bacteria populations rebuild in root hairs, they again accumulate in the hair tips, subsequently triggering another ejection event.