Cytokinin regulates differentially expression of PAHK-GUS constructs in transgenic Arabidopsis thaliana plants

The expression regulation by cytokinin of genetic constructs P AHK2 - GUS, P AHK3 - GUS , and P AHK4 - GUS in transgenic Arabidopsis thaliana (L.) Heynh plants bearing the gene encoding β-glucuronidase ( GUS ) under the control of the promoter of one of three genes encoding histidine protein kinases, which are membrane receptors of cytokinin was studied. In 4–5-day-old etiolated A. thaliana seedlings, treatment with cytokinin resulted in the strongest expression activation of the constructs P AHK2 - GUS and P AHK3 - GUS . The same constructs were activated by cytokinin also at the seedling transit from scoto- to photomorphogenesis. Long-term seedling growing in darkness on medium containing cytokinin resulted in the substantial promoter activation of the gene encoding the histidine kinase AHK2. In the leaves of three-week-old plants with actively functioning chloroplasts, treatment with cytokinin mainly stimulated expression of the construct P AHK3 - GUS . In detached senescing leaves, treatment with cytokinin retarded the loss of chlorophyll but did not affect significantly GUS activity under both light and darkness conditions in either of tested lines containing GUS gene under the control of promoters of histidine kinase genes. At the same time, cytokinin activated the promoter of the gene of primary response to cytokinin in the construct P ARR5 - GUS . Thus, in the studied test-system, treatment with cytokinin of A. thaliana plant grown in darkness or in the light affected differently the expression of histidine kinase genes in dependence of plant age, conditions of plant cultivation, and plant physiological state.