RNA gel blot analysis of siRNAs in virus-inoculated ihprolC-PP197 transgenic plants. Low molecular weight RNA isolated from apical leaves of untransformed control plant (lane 1) and transgenic plants either 2 days (lanes 2 and 3) or 42 days (lane 4) after inoculation were hybridised to hydrolised single stranded 32P-labeled RNA probe corresponding to the 134–330 region of the PPV genome (Panel A). Panel B shows the same blot hybridised to a riboprobe corresponding to the 1334–1831 region of the PPV genome. 21 and 23 nt-long RNA oligoribonucleotides were used as molecular standards. RNA amount loaded per lane was: Lane 1, 2 and 3, 40 μg; Lane 4, 27 μg.