Cytokinin-induced gene expression in cultured green cells of Nicotiana tabacum identified by fluorescent differential display

The cell growth and plastid development of cultured green tobacco cells wer e maintained by the phytohormone cytokinin. After subculture into cytokinin -free medium, when cytokinin treatment was resumed, physiological changes i nduced by cytokinin were analyzed. Changes in chlorophyll biosynthesis and photosynthetic gene expression were observed 1 week after cytokinin inducti on, and changes in cell growth were observed 2 weeks after cytokinin induct ion. Two cytokinin-induced genes (cig) were isolated from these cells using the fluorescent differential display technique. Northern analysis confirme d that expression of these cig was induced by both natural and synthetic cy tokinins. The expression of cig1 was also induced by abscisic acid, and its cDNA sequence was similar to the proline dehydrogenase gene. The expressio n of cig2 is specific to cytokinin and is not induced by other phytohormone s, The amino acid sequence encoded by cig2 is similar to the GDP/GTP exchan ge factor eIF2B, which regulates translation initiation. The expression of these cig suggests a complex induction system involving cytokinin and other phytohormones.