A transverse section of a transgenic Arabidopsis flower that expressesGA1promoter-reporter (glucuronidase, GUS). GA1 encodes a key enzyme in plant hormone gibberellin biosynthesis. The GUS activity was detected by the X-Gluc staining, which is in pink in dark-field. The GA1 promoter activity is high in pollen and in anther sac walls. a, anther; p, pollen More info