Immunological detection of syringopeptins produced by Pseudomonas syringae pv. lachrymans

Several strains of plant pathogenic Pseudomonas are known to produce phytotoxic lipodepsipeptides (syringomycin, syringopeptins and related compounds) in vitro. However, detection of these compounds in organic extracts from diseased plant tissues has been attempted by chromatographic methods for syringomycin only. A macromolecular derivative of syringopeptins (KLH-SP(25A+B)) was used to raise polyclonal antibodies in rabbit. The antiserum was able to recognize free syringopeptins (SP₂₂ and SP₂₅) with an estimated detection limit of 0.05 μg per well in the indirect ELISA, and 0.01 μg per well in the competitive ELISA. Cross-reaction with other structurally related lipodepsipeptides, e.g. syringomycins and pseudomycin A, was less than 20%. Using the competitive ELISA method developed in this study, relatively abundant quantities of the toxins, i.e. approximately 0.1 mg of syringopeptins per gram fresh tissue, were detected when an aqueous extract from cotyledons of zucchini infected with a strain of P. syringae pv. lachrymans was tested.