Resistance of Tomato Cultivars to Tobacco Mosaic Virus IV.

Induction of Resistance in Tomato Cultivars by the Antibiotic and TMV Protein

Abstract

An antibiotic, chromomycin A₃ (CMA) which was isolated in Japan and has been known to inhibit DNA dependent RNA synthesis as actinomycin D (AMD) does, and tobacco mosaic virus (TMV) protein obtained by the acetic acid method were introduced through the roots or stems into tomato cultivars susceptible or resistant to TMV. TMV concentration in tomato leaves was determined by measuring OD₂₆₀ of the resultant virus nucleoprotein that was precipitated by adding 0.25 saturated ammonium sulfate to the extract clarified by chloroform. Introduction of 5-30ppm of CMA for 7 days following TMV inoculation reduced the virus concentration in leaves of resistant cultivars as compared with those in untreated plants, but did not in the susceptible cultivar. Ten ppm of CMA introduced into the resistant cultivar for 1 day following inoculation was proved sufficient to induce resistance. By introducing 2-17μg of TMV protein into tomato plants through the roots or stems, TMV concentration in both susceptible and resistant cultivars was reduced below that in untreated plants, suggesting that TMV protein induced resistance. Polyacrylamide gel electrophoresis and isoelectric focusing for peroxidase (PO) isoenzymes revealed that, in the susceptible cultivar treated with CMA, number of bands in the gel and PO activity of each band decreased as compared with untreated control, while the resistant cultivar showed an increased PO activity. Introduction through the stems of TMV protein caused an increase in the activity of PO isoenzymes in both the susceptible and resistant cultivars. Especially, II group of isoenzymes which has an isoelectric point at pH 6.0 was increased in its intensity by TMV protein treatment. Based on these facts obtained, efficient inducers for resistance against virus in tomato cultivars and the relation between the induction of resistance and PO activity are discussed.