Peroxidases in the early responses of different potato cultivars to infection by Potato virus YNTN

Peroxidases (POXs) were investigated in three cultivars of potato (Solanum tuberosum) with different susceptibilities to infection by Potato virus Y-NTN (PVYNTN). Soluble, ionically-bound and covalently-bound POXs were analysed over 24 h post inoculation (hpi) in bottom inoculated leaves, upper intact leaves, and in roots. The first changes were observed at 3 hpi when the activity of ionically-bound POXs increased significantly in the inoculated leaves of tolerant cv. Pentland Squire and of resistant cv. Sante. The most pronounced changes were found in the resistant variety, where the increase was twice that in control plants. In contrast, in the inoculated leaves of susceptible cv. Igor, there was a decrease in ionically-bound POXs, accompanied by a two fold increase in the activity of covalently-bound POXs. Also at 3 hpi, cv. Sante showed increased activity of all three types of POXs in the upper intact leaves. Over the period of the experiment, enhanced activity of soluble POXs, correlated with the virus infection, was observed in both types of leaves of the susceptible cv. Igor. However, in resistant cv. Sante, the upper intact leaves of virus-inoculated plants showed a more intense but transient early response of soluble POXs. Part of a new POX gene was isolated from leaves of potato cv. Igor. A nucleotide sequence of 394 bp was determined and the abundance of the POX transcript was analysed by real-time PCR. There was no correlation between PVYNTN infection and the abundance of the transcript.