Toxins in plant disease: structure and mode of action

Synthesis and physiological activity of ureas and amides with carvone residues

The synthesis and herbicidal activity of ureas and amides with carvone residues were examined. (S)-(+)-(1) and (R)-(-)-Carvone(2) were converted to the respectively, primary amines(3) and (4) by oximation and reduction with LiAlH(4). Primary amine derivatives were further converted into the urea and amide compounds (3a) approximately (3e) and (4a) approximately (4e). The herbicidal activity of products (3a) approximately (3e) and (4a) approximately (4e) towards weeds found in a paddy field and field was measured in the pot. Products (3a) showed a particularly strong inhibitory effect on the growth of Amaranthus retroflexus(AR) and Setaria viridis(SV).

Leaf Infections: Siderochromes (Natural Polyhydroamates) Mimic the "Green Island" Effect

Topical application of as little as 5x10(-12) moles of pure siderochromes (polyhydroxamate iron-transport compounds from bacteria and fungi) onto detached bean leaves causes spots of chlorophyll retention that are surrounded by chlorotic halos. These spots appear similar to "green islands" that are caused by certain fungal infections on leaves and are somewhat similar to zones where senescence is delayed by cytokinin.

Pathotoxin-Induced Disease Resistance in Plants

Primary leaves of bean plants treated with nonphytotoxic concentrations of the pathotoxin victorin were rendered highly resistant to two plant viruses. Leaves treated with higher concentrations of victorin became necrotic. These effects on plants that are resistant to victorin and to the fungus that produces it lend support to the hypothesis that activation of a defensive self-repair mechanism may account for resistance to this highly selective pathotoxin.