Studies On Induced Accumulation Of Tobacco Pathogenesis-related Proteins By Ningnanmycin And Possible Role Of Ningnanmycin In Induced Resistance In TMV Infected Tobacco Leaves

Plants, like humans, actively defend themselves against pathogenic organisms. Plants respond to pathogens by activating broad-spectrum innate immune responses. It has been well established that in plants the hypersensitive reaction (HR) is not only restricted to the infected tissues, but also may occur in distal uninfected leaves termed systemic acquired resistance (SAR). The onset of SAR is characterized by induction of expression of a distinct set of defense genes, the SAR genes. SAR genes primarily encode acidic pathogenesis-related (PR) proteins, which found accumulated in wash fluids from the intercellular spaces of the leaves, are used as molecular markers for the pathogenesis-induced defense mechanism. PR proteins are plant species-specific proteins produced in response to infection with viruses, fungi or bacteria, and stress conditions. Cooperation of PR proteins spatially and temporally displays multiple effects within the plant and possesses antimicrobial activity. Measuring expression levels of PR genes is an appropriate method for determining anti-pathogenic levels in plants.Tobacco mosaic virus (TMV) is a broad-host seriously harmful plant pathogen. Infection of TMV results in severe leaf distortion and chlorosis, lower photosynthetic electron transport rates, heavily metabolic suppression in plant cells, and different inhibition of gene expression in nucleus and plastids.Ningnanmycin is a cytosine nucleoside type plant antibiotic isolated from fermentation broth of Streptomuces noursei var, xichangenesis. Hu Houzhi et al. found the controlling efficiency of Ningnanmycin on virus diseases of tobacco wasabout 50-90% in field application and in green house experiments. Ningnanmycin could also obviously improve the inside quality of tobacco. But the functional mechanisms of Ningnanmycin are not well understood.In this study, we compared induced accumulation of acidic PR proteins spatially and temporally in tobacco leaves, the expression levels of large subunit and small subunit of ribucose-l,5-bisphosphate carboxylase/oxygenase, and different induction of acidic PR proteins in two leaf types of the same tobacco species. To address whether Ningnanmycin may be involved in induced resistance of tobacco to TMV, experiments were performed to compare the expression levels of acidic PR proteins, and the accumulation levels of AP24 transcripts in tobacco leaves by RNA gel blot analysis with different treatments in in virto passivating experiments, preventing experiments and treating experiments. We also measured the quantity of total chlorophyll and the individual quantities of chlorophylls a and b in treated leaves and upper leaves, and observed the appearances of leaves and plants.The results of our studies showed PR proteins could be induced systemically byNingnanmycin in treated leaves and upper leaves. Furthermore, PR proteins continued to accumulate to high levels in a relatively long time course. We also found that effect of Ningnanmycin is correlated with type of plant cultivars.In study of the effect of Ningnanmycin on TMV, we found the treating effect and i/i virto passivating effect were better than preventing effect. Furthermore, the plants developed systemic acquired resitance during the process. It suggested a possible involvement of Ningnanmycin in resistance to TMV indirectly.