Tissue-Specific GUS Activity under the Control of the AtOCT4 Promoter. In the stem of PAtOCT4-plantsGus activity was weak, a stronger signal was present in the stem of secondary inflorescences (A, E). In the flowers, GUS activity can be found in young siliques (B). Opening of the siliques reveals that the staining is restricted to the veins of young (C) and mature siliques (D). Cross sections of the stem localize the staining to the phloem and cells medial to the xylem (F). In rosette leaves GUS activity can be found in the vasculature (G).