Involvement of Phaseolotoxin in Halo Blight of Beans

Phaseolotoxn ([N6-phospbosulfamyl]oruithylaanylbomoarginine) is produced by Pseudomonas phaseolicola (Brkbh.) Dows. in liquid cultwre. When phaseolotoxin was applied to leaves of bean (Phaseolus vulgars L.) at 0.1 to 1 nmoles/g fresb weight of leaf by a prick-asay procedure, the chacteristic "halo" symptom of bean halo blight disea developed after 24 to 48 hours. At higher concentntions (10100 nmoles/g frb weight) the systemic symptoms, whic are commonly a feature of diseased plants, also developed after 24 to 48 hour. When appied to bean leaves, phaseolotoxin was rapidly broken down by the sequential removal of homoarginine and alanine. N8Phosphosulfamylornithine was the major product formed, although phosphosulfamate and unreacted pbaseolotoxin were also present. When P. phaseolicola infected bean plants, very little phaseolotoxin was detected within the plant, but the amount of N8-phosphosulfamylornithine formed was sufficient to account for the observed chlorosis, the omithine accumulation, and the systemic symptoms. NW-Pbosphosuifamyloruithine therefore seemed to be the main functional pbytotoxin of bean halo blght disease. When 35S-phaseolotoxin was applied to primary leaves, 35S (assumed to be a mixtre of pbaseolotoxin, N5-phosphosulfamylornithine, and pbospbosulfamate) was actively loaded into the fine veins of the leaf and moved tbrough the plant in the vascular system at a speed greater than 3 cm/bour, particularly toward the apical and lateral buds and the root tips. Certain factors which affect phloem transport (arsenate, cold) affected toxin movement snd the expression of systemic symptoms. Autoradiography suggested that the 35S was transported in the phloem. A model for the involvement of pbaseolotoxin in balo blight disease is presented.