Figure 2.

Cytokinin-dependent expression of lacZ in E. coli (ΔrcsC, cps∷lacZ) expressing ZmHKs. E. coli strains harboring pIN-III-ZmHK1 (A), pIN-III-ZmHK2 (B), pIN-III-ZmHK3a (C), or pIN-III-ZmHK3b (D) were cultured in the absence (NC, negative control) or presence of the cytokinin indicated at 1 μm. tZ, trans-zeatin; tZR, trans-zeatin riboside; iP, isopentenyladenine; iPR, isopentenyladenine riboside; cZ, cis-zeatin; cZR, cis-zeatin riboside; BA, benzyladenine; TDZ, thidiazuron. tZ, iP and cZ are free-base species of isoprenoid cytokinins, and tZR, iPR, and cZR are their nucleoside forms, respectively. BA is a free-base aromatic cytokinin, and TDZ is a synthetic phenylurea cytokinin. Culture period was 12 h for ZmHK1 and ZmHK2, 4 h for ZmHK3a, and 8 h for ZmHK3b. The cells were harvested and the β-galactosidase activity was measured with o-nitrophenyl-β-d-galactopyranoside (ONPG) as a substrate. The values presented are means of triplicate assays with sd. A dashed horizontal line indicates the negative control value in each case.