Chenopod salt bladders deter insect herbivores

Trichomes on leaves and stems of certain chenopods (Chenopodiaceae) are modified with a greatly enlarged apical cell (a salt bladder), containing a huge central vacuole. These structures may aid in the extreme salt tolerance of many species by concentrating salts in the vacuole. Bladders eventually burst, covering the leaf in residue of bladder membranes and solid precipitates. The presence of this system in non-halophytic species suggests additional functions. I tested the novel hypothesis that these bladders have a defensive function against insect herbivores using choice, no choice, and field tests. Generalist insect herbivores preferred to feed on leaves without salt bladders in choice tests. In no choice tests, herbivores consumed less leaf matter with bladders. In a field test, leaves from which I had removed bladders suffered greater herbivory than adjacent leaves with bladders. Solutions containing bladders added to otherwise preferred leaves deterred herbivores, suggesting a water-soluble chemical component to the defense. This bladder system has a defensive function in at least four genera of chenopods. Salt bladders may be a structural defense, like spines or domatia, but also have a chemical defense component.