Tissue-Specific GUS Activity under the Control of the AtOCT3 Promoter. POCT3-Gus plants show staining in the basal part of the stem (A) and in seeds in young siliques only (B,C) but not in mature seeds (C). Cross section of the stem localized the staining to the epidermis and parenchyma cells below the epidermis (D). The stems of secondary inflorescence show strong staining (E). In leaves, staining was visible throughout the leaf blade and the basis of trichomes (F), cross section of a leaf shows GUS signal at lower and upper epidermis (G).