HL-grown plants demonstrate higher silencing efficiency affecting both mRNA levels and siRNA production. (A) Northern blot detection for mGFP5:ER and mGFP4 in 16C, 6.4 fully silenced and 6.4 non-silenced leaf tissue, from plants grown under HL and LL conditions. 6 h and 2.5 h of autoradiographic exposure time were applied in the higher and middle panels, respectively. UBI3 transcripts and 18S/chloroplast rRNA ethidium bromide staining served as loading controls. (B) Detection of GFP-siRNAs produced under HL and LL in fully silenced leaf tissue. (C) Detection of Nib-siRNAs derived from an hpNibRNA in plants grown under HL and LL. U6 probing was used as loading control (lower panels). GFP, green fluorescent protein; HL, high light intensity; LL, low light intensity; UBI3, ubiquitin; Nib, Plum pox virus polymerase; hp, hairpin.