Host Plant Resistance to Pathogen with Reference to Induction of Systemic Acquired Resistance (SAR) in Tobacco (Nicotiana Tabacum Var. Samsun) When Infected with Tobacco Mosaic Virus (TMV)

Abstract

A model study based on induction of SAR via infecting different lines of tobacco (Nicotiana tabacum var. Samsun) with Tobacco mosaic virus (TMV) was carried out at the Department of Applied Biology, University of Helsinki, Finland in December, 2006. The objective was to demonstrate the onset of defence response, spread of SAR in tobacco plants infected with TMV and detection of expression of marker gene, PR protein gene (PR1) using northern blotting and real time polymerease chain reaction (PCR). Localized necrosis was observed at 3 and 10 days post inoculation (dpi) only in TMV-inoculated NN plants in contrast to absence of similar localized symptom in the corresponding inoculated nn plants except systemic yellowing at 10 dpi. The data generated by northern blot analysis as well as real-time PCR showed existence of variation among experimental treatments with respect to PR1 gene expression. Northern blotting and real-time PCR gave similar results except a difference that was observed for sample 10 probably signifying high precision and sensitivity of real-time PCR in indicating PR1 expression compared to northern blotting. The RNA ladder was not visible in agarose gel and it was not possible to observe the actual result. This confirmed the importance of proceeding to the application of northern blotting. The result of this study indicated localized induction of necrotic lesions in infected tobacco var. Samsun (NN) as indicator for the HR programmed cell death and PRl expression as indicator for SAR in systemic leaves. All plants of nn variety are susceptible and showed only systemic mosaic symptoms in contrast to localized lesions expressed in NN plants. The result of this study indicated that the NN gene in TMV-infected tobacco var. Samsun carrying N allele recognized the corresponding Avirulence gene of the virus inducing the SAR in systemic leaves as indicated via expression of PR1 protein and hypersensitive reaction (HR) in infected leaves as visualized by localized necrosis in infected leaves. This is in agreement with the theory of gene-for-gene interaction in plant defence responses. Keywords : Gene-for-Gene; Inoculation; Pathogenesis-Related proteins East African Journal of Sciences Vol. 2 (2) 2008: pp. 184-188