UB19 and UBC20 mRNA accumulation in various Arabidopsis organs, during re-initiation of mitotic activity in leaf strip cultures and in a cell-suspension culture. A, Total RNA was extracted from silique (lane 1), floral buds (lane 2), open flowers (lane 3), leaves (lane 4), stems (lane 5), roots (lane 6), and 3-d-old germinating seeds (lane 7); B, total RNA was extracted from leaf strips (LS) incubated in a medium suitable for cell division for 0 h (lane 8), 24 h (lane 9), 48 h (lane 10), and 72 h (lane 11). The blots were probed successively with UBC19, UBC20, histone H4, and 25S rRNA probes. C, Growth curve of the cell-suspension culture determined by the fresh weight (top right panel). Northern analysis from total RNA extracted at different times during the culture (middle right panel). The RNA blot was probed with UBC19, histone H4, and 25S rRNA probes. UBC19 protein accumulation at different times during the culture (lower right panel). The western blot was probed successively with anti-UBC19 and anti-AtCUL1 polyclonal antibodies.