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Regulation of the Korean radish cationic peroxidase (KRCP) promoter by auxins–cytokinins are described in this study. Various fragments of the KRCP promoter have been cloned and transcriptionally fused to the GUS gene to transform tobacco BY-2 cells, arabidopsis, and tobacco plants. Cytokinins decreased the dose- and time-dependent GUS expression of the pBK12 construct in the BY-2 cells. In contrast, the GUS expression of the pBK12 construct was significantly induced by a low ratio of cytokinin to auxin, although the GUS expression was not observed in any organ of the transgenic arabidopsis and tobacco plants at any stage of normal development under no hormone treatment. The GUS activities of the pBK12 construct driven by a low ratio of cytokinin to auxin were over 400- and 58-fold higher in the leaves and stems, respectively, than in those of the untreated arabidopsis plants. The induced GUS staining was mainly localized in the leaves and stems treated with the low ratio of cytokinin to auxin. These results suggested that the promoter activity of the KRCP gene be up-regulated by the low ratio of cytokinin to auxin. The KRCP promoter exhibited a higher degree of specificity to a low ratio of cytokinin to auxin rather than to either auxin or cytokinin alone in tobacco and arabidopsis plants. To date this study provides the first evidence that the combination of cytokinin and auxin takes part more in the regulation of the activity of KRCP promoter than in each hormone alone.

The Korean radish cationic peroxidase promoter (KRPP) and the β -glucuronidase (GUS) gene were fused on the genome of tobacco BY-2 cells via Agrobacterium -mediated transformation method. A fragment of the KRPP comprising nucleotides −471 to +704 relative to the transcriptional initiation site confers constituent expression of GUS in transgenic tobacco BY-2 cells (BYK12). The expressed GUS activity was increased by as much as 40% at 577 nM gibberellic acid (GA 3 ). This increase was time and dose dependent. The abscisic acid (ABA) from 10 to 100 μM slowly decreased the GUS activity and at 100 μM reduced completely the inductive effect of GA 3 on GUS expression. Thus, GA 3 and ABA have antagonistic effects on the GUS expression mediated by the Korean radish cationic peroxidase promoter in transgenic BYK12 cells. Exogenous GA 3 activated the activity of the Korean radish isoperoxidases and also increased the intensity of two bands of Korean radish cationic isoperoxidases, when hypocotyl portions of the Korean radish seedlings grown in a green house for 10 days were examined using starch gel electrophoresis. However, ABA decreased the intensity of the Korean radish cationic isoperoxidase bands and also reduced the inductive effect of GA 3 in seedlings.