Northern blot showing expression of 7 maize IDD genes compared to ID1. Gene-specific probes are indicated on the right side. Tissues used include: S, stem below the apical region, Ap, apical region of plant, including 2 cm above apical meristem and leaf primordia. Sections 1, 2 and 3 are immature leaf sections from 2–4 cm, 4–6 cm and 6–8 cm above the apex, respectively. TL, immature flag leaf surrounding tassel primordium; T, pre-anthesis tassel; R, roots. The same B73 plant with 7 visible leaves was used for sections S, Ap, 1, 2 and 3. (A) Gene-specific probes derived from cDNAs of ZmIDDp1, ZmIDDp10, ZmIDDveg7 and ZmIDDveg9. The ZmCDC2 probe, which is detected in tissues with actively dividing cells, was used as a control . An arrowhead indicates the position of the ZmIDDp10 band. (B) Blot hybridized with specific probes to ZmIDD3, ZmIDD7, ZmIDD13 and an actin-specific probe.