Appearance of a Host Protein in Cucumber Plants Infected with Viruses, Bacteria and Fungi

Abstract

Electrophoretic analyses of extracts of cucumber leaves infected with Colleiotrichum lagenarium, Fusarium oxysporum f. sp. cucumerinum, Pseudomonas lachrymans, Erwinia tracheiphila, tobacco necrosis virus or cucumber mosaic virus revealed the presence of a protein band with an R_F value of 0.55–0.60 (based on mobility of bromophenol blue) on 10% polyacrylamide gel. This band was not evident in extracts of healthy or mechanically wounded leaves. The protein was not detected in uninfected leaves of infected plants, but it was detected in similar amounts in infected leaves and in secondarily challenged leaves of infected plants even though symptoms were not apparent on the latter. The protein had a molecular weight of approximately 16 000 d, was adsorbed on DEAE-cellulose, did not react with Schiff's reagent, and did not have ribonuclease activity. When injected into cucumber leaves, it did not inhibit germination of conidia of C. lagenarium or induce resistance against disease caused by the fungus.