Fig. 6

Activity of ATHB8 Promoter Variants. (A–D) First leaves 4 DAG (for simplicity, only half-leaves are shown). Confocal laser scanning microscopy. nYFP expression (look-up table — ramp in E — visualizes expression levels) driven by promoter variants (top right) with native ([TGTCTG]::nYFP, i.e. ATHB8::nYFP) (A), negligible ([TAGCTG]::nYFP) (B), lower ([TGTCAG]::nYFP) (C), or higher ([TGTCTC]::nYFP) (D) affinity for MP binding. Dashed white line: leaf outline. (F) nYFP expression level per cell expressed as mean gray value ± SE, nYFP expression domain length expressed as mean number of cells ± SE, and nYFP expression level per domain expressed as mean gray value ± SE. Local background levels were measured in image regions containing no features of interest as in [14, 100]. Difference between [TAGCTG]::nYFP expression levels in vein cell nuclei and [TGTCTG]::nYFP expression levels in vein cell nuclei, between [TGTCAG]::nYFP expression levels in vein cell nuclei and [TGTCTG]::nYFP expression levels in vein cell nuclei, and between [TGTCTC]::nYFP expression levels in flanking cell nuclei and [TGTCTG]::nYFP expression levels in flanking cell nuclei was significant at P < 0.001 (***) by F-test and t-test with Bonferroni correction. Sample sizes: 31 ([TGTCTG]::nYFP), 32 ([TAGCTG]::nYFP), 38 ([TGTCAG]::nYFP), or 35 ([TGTCTC]:nYFP) leaves; 538 ([TGTCTG]::nYFP), 91 ([TAGCTG]::nYFP), 296 ([TGTCAG]::nYFP), or 420 ([TGTCTC]::nYFP) vein cell nuclei, and 328 ([TGTCTG]::nYFP), 175 ([TAGCTG]::nYFP), 398 ([TGTCAG]::nYFP), or 1,144 ([TGTCTC]::nYFP) flanking cell nuclei. In [TGTCTG]::nYFP, [TAGCTG]::nYFP, and [TGTCAG]::nYFP, flanking cell nuclei were identified by means of RIBO::nCFP expression. In [TGTCTC]::nYFP, vein cell nuclei were identified by means of ATHB8::nCFP expression. Scale bars: 25 μm