A cyanogenic plant sets up a little cyanide bomb in the cell, Olsen explained. You have a cyanogenic glucoside basically a sugar with a cyanide group stuck onto it, in the cell vacuole, and then in the cell wall there is an enzyme required to hydrolyze the cyanide. If something damages the cell, these two compounds come into contact with each other and free cyanide is released. One gene, Li, encodes the enzyme, which is called linamarase; another gene, Ac, is responsible for the presence or absence of cyanogenic glucosides.
Olsens recent findings have revealed that plants that do not synthesize linamarase are lacking the Li gene altogether: the genes DNA is absent from genomes of these plants.
Olsen and colleagues are also testing hypotheses on why acyanogenic plants occur in cold climates. One poses that there are fewer herbivores in colder climates.
If a plant can get by without investing in all the resources it takes to be cyanogenic, it can concentrate those resources in other forms of growth and reproduction, then it would be out competing the plants that are cyanogenic, Olsen said.
Suicide not ruled out
The second hypothesis explores the lurid possibility of plant suicide. In hypothesis two, we question the role of frequent frosts. The frosts could cause cell rupture and the release of cyanide leading to autotoxicity. If cyanogenic plants are poisoning themselves in cold climates, then those plants will be at a disadvantage.
To examine both the weather factor and suicide possibility, Olsen and his colleagues are testing different types of clovers in freeze chambers at controlled temperatures to see if survival is higher for either acyanogenic or cyanogenic plants.
The advantage of the clover cyanogenesis system is theres already so much known about its ecology, Olsen said. What were able to do now is get to the molecular level and look at
|Contact: Kenneth Olsen|
Washington University in St. Louis