Transcriptional activation in sunflower embryos. Plant material was particle bombarded with a luciferase reference plasmid, the indicated chimeric GUS reporter gene (WT, Mut0, or MutP), and the Hsf effector plasmid combination shown in the top left corner: (−), no effector plasmid; (+), effector plasmids bombarded simultaneously. We show average reporter GUS activities normalized with luciferase (GUS/LUC, as in Prieto-Dapena et al., 1999), with bars indicating the ses. Data correspond to at least five independent experiments, with each plasmid combination repeated at least 25 times. Nonsignificant differences in reporter gene activities are indicated (P ≥ 0.05). Values for the significant statistical differences mentioned in the text were as follows: for the WT gene with effector plasmid(s) versus without effector plasmid(s), with LpHsfA2, F = 139.6, P = 0.0001; and with LpHsfA1 + LpHsfA2, F = 429.1, P = 0.0001. The induced level obtained with LpHsfA1 + LpHsfA2 did not differ from that of with LpHsfA1 M3 + LpHsfA2, F = 0.25, P = 0.61. In addition, the values obtained with LpHsfA1 + LpHsfA2 were significantly higher than the addition of reporter activities separately obtained with each Hsf (F = 27.35, P = 0.001). For the mutP gene with effector plasmid(s) versus without effector plasmid(s): with LpHsfA2, F = 41.4, P = 0.0001; and with LpHsfA1, F = 9.3, P = 0.021.