Evaluation of protein and total phenolics changes in susceptible and resistant varieties of tobacco (Nicotiana tabacum) leaves infected by PVY

Abstract
Background and objectives: The cultivated tobacco (Nicotiana tabacum) is a tropical and annual plant, consisting of a number of species or hybrids belonging to the Solanaceae family. Bio-chemical reaction to viral infection is different for various plants .One of the most important defensive mechanisms of the host plant against pathogen agents, is biochemical defense and their related complex reactions. Potato virus Y (PVY) from the Potyviridae family has a worldwide distribution and is one of the common viruses in tobacco fields. Different tobacco varieties show various reactions against these virus strains.
Materials and methods: In this study, total protein, total phenol changes and enzymatic activity of peroxidase and polyphenoloxidase of leaves from two tobacco cultivars, called VAM (resistant) and K326 (susceptible) infected by PVYO were investigated at 1, 2, 3, 4, and 5 days after mechanical inoculation The experiment was conducted in a factorial pattern on the basis of completely randomized design with four replications in the greenhouse condition. To confirm the presence of virus, the optical absorption (OD) in the samples were tested by DAS-ELISA using a PVY polyclonal antibody.
Results: The analysis of variance with multiple range Duncan test for the results showed the total protein of VAM cultivars was more than inoculated K326 cultivars and the control samples. During the days after inoculation except the third day, their difference was not significant. The highest total protein was observed in the first and fifth days after inoculation and in the inoculated VAM cultivars and the lowest total protein was recorded in the second and fourth days after inoculation and in the K326 cultivars. The highest total phenol was observed in fifth days after inoculation which was significantly different compared to other intervals (P≤ 0.01). Amount of total phenol in the inoculated cultivars was higher than control samples and showed a significant different (P≤ 0.01).
Conclusion: Peroxidase activity in the inoculated cultivars was higher than control one and it was significantly higher in the K326 than VAM cultivars. Peroxidase and polyphenol oxidase activity of tobacco leaves in VAM cultivar during the days after inoculation was significantly (P≤ 0.01) lower than K326 cultivar. The difference in enzymatic activity could be related to the type of cultivar, inoculation treatment and time after inoculation. The OD of K326 was higher than its value in VAM cultivar. Also, correlation between these parameters was very low. There was a relatively high and positive correlation (R2=0.546) between the enzymatic activity of peroxidase and polyphenol oxidase.
Key words: Potato virus Y, DAS-ELISA, total protein, total phenol, peroxidase and polyphenol oxidase.