Fig. 4. The extrafloral nectaries of Gossypium. (A) Extrafloral nectaries are located on midveins on the abaxial sides of the leaves. (B) The secretory structure is composed of trichomes that densely populate the concave region of the midvein. (C,D) Secretory trichomes are multicellular and small cytoplasmically dense parenchyma cells are located below the trichomes. (E) Expression of GhCRC in an involucral bract nectary localized by in situ PCR with a green signal representing the fluorescence signal from in situ PCR products of GhCRC. (F) GhCRC is highly expressed in the papillar cells and subtending cells in a leaf nectary. (G) Expression of GhCRC during extrafloral nectary development as monitored by semi-quantitative RT-PCR. 1-29, G. hirsutum; 30-32, G. tomentosum; left lane, actin; right lane, GhCRC (or GtCRC) amplified from same cDNA for actin under the same PCR condition. The upper bands in lanes 27-29 are from genomic DNA; the lower bands represent cDNA. 1, 3 mm whole leaf; 2, 5 mm whole leaf; 3, 1 cm whole leaf; 4, 1.4 cm leaf blade; 5, 1.4 cm leaf vein; 6, 2.8 cm leaf blade; 7, 2.8 cm leaf vein; 8, 2.8 cm leaf nectary; 9, 7 cm leaf blade; 10, 7 cm leaf vein; 11, 7 cm leaf nectary; 12, 12 cm leaf blade; 13, 12 cm leaf vein; 14, 12 cm leaf nectary; 15, bract nectary of 1.5 cm flower; 16, rest of bracts; 17, sepals; 18, petals; 19, stamens; 20, carpels; 21, bract nectary of 6 cm long flower; 22, rest of bracts; 23, sepals; 24, petals; 25, stamens; 26, carpels; 27, root of seedlings; 28, hypocotyl of seedlings; 29, apex of seedlings; 30, root of seedlings; 31, hypocotyl of seedlings; 32, apex of seedlings.