Notes

Movement: They absorb oxygen through their skin by diffusion. Many are parasitic and have the same three cell layers as platyhelminthes (ectoderm, endoderm, and mesoderm). Nematodes have a hydrostatic skeleton, which is a closed body compartment filled with fluid (Goldberg). They are one of the most abundant animals on the planet as just a handful of soil can contain thousands of nematodes. They feed on bacteria, fungi, and other nematodes (“The Roundworms”).

Defense: The cuticle of the nematode functions as a hydroskeleton, a barrier, and a sensory array. As a hydroskeleton, the cuticle controls the long muscles along the epidermis. As a barrier, it provides protection. As a sensory array, it detects changes in the environment (“The Roundworms”). Parasitic nematodes release effector cells to prevent the host immune response. The surface coat of the cuticle, consisting of lipid and protein molecules is shed as the nematode moves, shedding bacteria but also confusing the plants about the nematode’s presence. In addition, in plant cells, the effector cells suppress pathogen-triggered immunity (PTI), a pathogen associated molecular pattern (PAMP). PAMP triggered PTI is the first line of defense in the host cell, starting the production of salicyclic acid (SA). This production will increase callose thickening of cell walls and the initiation of active oxygen defense responses (hydrogen peroxide and superoxide) which may initiate localized apoptosis, a hypersensitive response. Thus for a nematode to be successful in infecting this plant cell, it must suppress SA production. One possible way to disrupt SA production is for the nematode to release chorismate mutase, produced in its esophageal glands. In the PTI signaling pathway, chorismate is transformed into SA. Chorismate mutase from the nematode reduces chorismate and thus SA, so defense mechanisms are not triggered (Ferris).